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ROOFING INSPECTION & REPAIR
AGE OF ROOFING
AMERICAN CEMWOOD ROOFING
ARCHITECTURE & BUILDING COMPONENT ID
ASBESTOS IDENTIFICATION IN buildings
ASBESTOS CEMENT ROOFING
ASBESTOS MATERIAL REGULATIONS
ASBESTOS REGULATION Update
ASPHALT ROOF SHINGLES
ATTIC LEAKS, CONDENSATION & MOLD
BEST CONSTRUCTION PRACTICES GUIDE
BEST ROOFING PRACTICES
Attic Ventilation - Best Practices
ASPHALT SHINGLE PROPERTIES
ASPHALT SHINGLE RE-ROOF GUIDE
ASPHALT SHINGLE INSTALLATION
ASPHALT SHINGLE UNDERLAYMENT SPECS
ASPHALT SHINGLE VALLEY FLASHING
ASPHALT SHINGLES on VERY STEEP ROOFS
ASPHALT SHINGLE RE-ROOF GUIDE
BUR Built-Up Roof Installation
CLAY, CONCRETE, FIBER CEMENT TILE INSTALLATION
CLAY TILE ROOF SLOPE, DECK & UNDERLAY
CLAY TILE ROOF BATTENS & STACKING
CLAY TILE ROOF CONNECTIONS
CLAY TILE WIND & SEISMIC CONNECTORS
CLAY TILE EAVES, HIP & RAKE DETAILS
CLAY TILE ROOF BATTENS & STACKING
CLAY TILE ROOF CONNECTIONS
Cooling Load reduction by Attic Venting
EPDM Roof Installation
FLASHING, CHIMNEY Mistakes & Leaks
FLASHING, CLAY TILE ROOFS
FLASHING WOOD ROOF DETAILS
GALVANIC SCALE & METAL CORROSION
GALVANIZED STEEL ROOFS
Ice Dams Preventing on Roofs
LEAD in ROOFING, EFFECTS
Low-Slope Roofing Best Practices Guide
METAL ROOF LIFE EXPECTANCY
METAL ROOF COATINGS & PAINTS
METAL ROOF EXPOSED FASTENER SYSTEM
METAL ROOF EXPOSED FASTENER FLASHING
METALS USED IN ROOFING
Modified Bitumen Roof Installation
MODULAR METAL ROOF SHINGLE SYSTEM
Roll Roofing Installation
STANDING SEAM METAL ROOF INSTALLATION
SUPPLIERS, Roofing Materials & Equipment
TERNE METAL ROOFING
UNDERLAYMENT BEST PRACTICES
Underlayment for Standard Slopes
Underlayment on Low Slope Shingle Roofs
Underlayment Flashing in Freezing Climates
VENTILATION, ROOF BEST PRACTICES
Venting Tight Cathedral Ceilings
Walkable Roof Membranes
WOOD ROOF MAINTENANCE
WOOD ROOF SHEATHING, UNDERLAYMENT
WOOD ROOF SHINGLE PROPERTIES
WOOD SHINGLES, RE-ROOFING WITH
Wood Roof Slope & Exposure Tables
WOOD ROOF SHEATHING, UNDERLAYMENT
Wood Roof Hip and Ridge Specifications
Zinc Metal Roofing
BUILT UP ROOFS
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY INSPECTION & REPAIRS
CHOOSING A ROOFING CONTRACTOR
CLAY TILE ROOFING
CLAY, CONCRETE, FIBER CEMENT TILE INSTALLATION
COLD WEATHER ROOF TROUBLE
DEBRIS STAINING on ROOFS
DECKS, ROOFTOP CONSTRUCTION
DEFINITIONS of ENGINEERED WOOD OSB LVL etc
DISASTERS: BUILDING INSPECTION & REPAIR
EARLY ROOF FAILURE DIAGNOSTIC QUESTIONS
EXTERIOR WALL SIDING TRIM & FINISHES
FELT UNDERLAYMENT REQUIREMENTS
FIBER CEMENT & FIBERBOARD ROOFING
FIRE RATINGS for ROOF SURFACES
FIRE RETARDANT PLYWOOD
FLASHING on BUILDINGS
FLASHING, ASPHALT SHINGLE VALLEYS
FLASHING, CHIMNEY Mistakes & Leaks
FLASHING, CLAY TILE ROOFS
FLASHING MEMBRANES PEEL & STICK
FLASHING for METAL ROOFS
FLASHING ROOF WALL DETAILS
FLASHING ROOF-WALL SNAFU
FLASHING SIDING DETAILS
FLASHING WALL DETAILS
FLASHING WINDOW DETAILS
FLASHING WOOD ROOF DETAILS
FLAT ROOF MOISTURE & CONDENSATION
GALVANIC SCALE & METAL CORROSION
Green House or Solarium Roof Leaks
GUTTERS & DOWNSPOUTS
HAIL DAMAGED SHINGLES
HEAT TAPES & CABLES on Roofs for Ice Dams
HOT ROOF DESIGNS: Un-Vented Roof Solutions
HOUSEWRAP INSTALLATION DETAILS
HUMIDITY LEVEL TARGET
ICE DAM PREVENTION
INSECT INFESTATION / DAMAGE
INSULATION IDENTIFICATION GUIDE
INSULATION INSPECTION & IMPROVEMENT
LEAD POISONING HAZARDS GUIDE
LEAKY ROOF DIAGNOSIS & REPAIR
LEED GREEN BUILDING CERTIFICATION
LOW SLOPE ROOFING
MASONITE WOODRUF FIBERBOARD ROOFING
MEMBRANE & SINGLE PLY ROOFS
MODIFIED BITUMEN ROOFING
NOISE / SOUND DIAGNOSIS & CURE
NOISE CONTROL for ROOFS
PLASTIC ROOFING TYPES
ROLL ROOFING, ASPHALT
ROOF ARCHITECTURAL STYLES - PHOTO GUIDE
ROOF CLEANING RECOMMENDATIONS
ROOF COLOR RECOMMENDATIONS
ROOF DORMER TYPES - PHOTO GUIDE
ROOF INSPECTION SAFETY & LIMITS
ROOF NOISE TRANSMISSION
ROOF VENTILATION SPECIFICATIONS
ROOFING FELT UNDERLAYMENT REQUIREMENTS
ROOFING MATERIALS, Age, Types
ROOF NOISE TRANSMISSION
ROOFING TILE SHAPES & PROFILES
ROOFING UNDERLAYMENT BEST PRACTICES
SIDING TYPES, INSTALLATION, DEFECTS
SLATE ROOF INSPECTION & REPAIR
SNOW GUARDS & SNOW BRAKES
STAINS on & in BUILDINGS, CAUSES & CURES
STAIN DIAGNOSIS on BUILDING EXTERIORS
STAIN DIAGNOSIS on BUILDING INTERIORS
STAIN DIAGNOSIS on ROOFS
STAIN DIAGNOSIS on STONE
STANDARDS for ROOFING
STONE CLEANING METHODS
TEST LABS - ROOF SHINGLE
Thermal Expansion Cracking of Brick
THERMAL EXPANSION of HOT WATER
THERMAL EXPANSION of MATERIALS
THERMAL IMAGING, THERMOGRAPHY
THERMAL IMAGING MOLD SCANS
THERMAL MASS in BUILDINGS
TREES & SHRUBS, TRIM OFF BUILDING
TRUSS UPLIFT, ROOF
TRUSSES, Floor & Roof
UNDERLAYMENT REQUIREMENTS on ROOFS
WALK-ON ROOF SURFACES
WARRANTIES for ROOF SHINGLES
WALL CONSTRUCTION BARRIER vs CAVITY
WATER ENTRY in buildings
WIND DAMAGE to ROOFS
WINDOWS & DOORS
WINTERIZE A BUILDING
WOOD SHAKE & SHINGLE ROOFING
WORKMANSHIP & ROOF DAMAGE
ZINC METAL ROOFING
This article series discusses best practices in the selection and installation of residential roofing.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Also see the roofing article links listed at Related Topics and our roofing home page: ROOFING INSPECTION & REPAIR.
Details about the properties of asphalt roof shingles are found at Asphalt Shingle Properties. Excerpts are below.
Asphalt shingles, which cover 80 to 90% of residential roofs, have undergone much change in the last 20 to 30 years. Until the late 1970s, all asphalt shingles were manufactured from a heavy organic felt mat that had established a reputation for both strength and flexibility and generally outlasted their 15- to 20-year life expectancy.
Since their introduction in the late 1970s, fiberglass shingles have come to dominate the market, accounting for over 90% of shingles sold today. However, premature failure of some fiberglass shingles in the 1980s and 1990s tarnished the product’s reputation and spawned a number of lawsuits and resulted in a toughening of standards and a general improvement in fiberglass shingle quality. Details about these fiberglass shingle problems are at CRACKS in FIBERGLASS SHINGLES.
Asphalt Roof Shingle Quality
Shingle quality is often difficult to determine visually since it is based largely on hidden factors such as the strength of the reinforcing mat (organic felt or fiberglass), the strength and flexibility of the asphalt, and the amount and type of fillers used. In most cases, however, the guidelines outlined below can help to select shingles that perform as promised.
Organic Felt vs. Fiberglass Asphalt Shingles
Organic shingles are built around a thick inner mat made from wood fibers or recycled paper saturated with soft asphalt. Fiberglass shingles, on the other hand, use a lightweight nonwoven fiberglass held together with phenolic resin.
Both shingles are then coated on top with a layer of harder asphalt and fillers and topped with colored stone to create a decorative surface and protect against ultraviolet light.
A thin layer of asphalt on the bottom is coated with a nonsticking dusting that keeps the shingles from sticking in the bundle. Each type has its pros and cons. Table 2-2 below compares the pros and cons of organic asphalt shingles (Standard ASTM D255) and fiberglass based asphalt shingles (Standard ASTM D3462).
Organic Asphalt Roof Shingles: Characteristics
In general, organic shingles have better tear resistance and resistance to nail pull-through than fiberglass shingles, making them less likely to blow away during a cold weather installation when they have not yet had a chance to seal. Also, some roofers find that organic shingles are more pliable and easier to work with in cold weather. On the downside, the organic mat is neither fireproof nor waterproof. Organic shingles therefore typically carry only a Class C fire rating.
Although uncommon, manufacturing defects that allow water penetration into the mat can lead to premature curling and cupping of organic shingles. Blistering and curling in warm climates has also been occasionally reported. Organic shingles cost more than comparable fiberglass shingles, but remain popular in colder regions and throughout Canada. With organic shingles, shingle weight tends to be a good predictor of performance and longevity since the added weight usually indicates a thicker mat saturated with more soft asphalt.
Fiberglass Based Asphalt Roof Shingles: Characteristics
Fiberglass shingles, built on a thin nonwoven fiberglass core, were first introduced in the late 1970s and now account for over 90% of the shingles sold. Because they use less asphalt, they are lighter and generally less expensive than organic shingles. Because fiberglass mats are more fire-resistant and moisture-resistant than felt, most fiberglass shingles carry a Class A (severe exposure) fire rating and are less prone to cupping and curling from moisture damage.
On the downside, fiberglass shingles are generally not as tear-resistant as organic shingles, making them more prone to blow-offs in cold weather when the shingles have not properly sealed. After they have sealed, they can still tear from movement in the sheathing, since fiberglass shingles have little give, unlike organic shingles. In this situation, if the bond strength of the adhesive strip exceeds the tear strength on a lightweight shingle, the shingles can crack.
Premature failure of some fiberglass shingles due to splitting or cracking led to a number of class-action lawsuits in the 1980s and 1990s. The problems were primarily with lower-end shingles with lightweight mats, types that have been largely eliminated from the market. But it still pays to buy ASTM-rated products from a reputable company that provides a good warranty.
Laminated Asphalt Roof Shingles: Characteristics
Also called “architectural” or “dimensional” shingles, these have two layers laminated together at the lower half of the shingle, giving the roof a thicker textured appearance with deeper shadow lines. Depending on the shape and size of the cutouts, half or more of the exposed shingle area is triple thickness and the rest double. With the added thickness and without the tabs, which typically wear out first in three-tab shingles, most laminated shingles carry longer warranties as well as higher wind ratings, some as high as 120 mph.
While not immune to the problems of other shingles, such as premature cracking, it is reasonable to expect good performance from a reputable brand. One problem unique to laminated shingles is the loosening of the bottommost piece of the shingle caused, in part, by nailing above the line where the double thickness ends (Figure 2-1).
On many laminated shingles, nails must be precisely placed so they are high enough to stay hidden while still penetrating both layers.
Definitions of Fire Ratings for Asphalt Shingle & Other Roofing Materials
Details about roof fire ratings and details about the applicable standards are at FIRE RATINGS for ROOF SURFACES. Excerpts are below.
Fire ratings for roof coverings describe how well the roof covering resists fires including the ability of the roof to resist catching fire from a lightning strike, if a spark or ember lands on it (say from a nearby chimney or from a forest fire), as well as the resistance to fire spread if the material is ignited.
Keep in mind that the purposes of roof covering fire ratings (to desribe the fire resistance of a roofing material), and the intent of roof fire resistance in general are to allow building occupants more time to escape in event of a fire, not to guarantee that the building nor its ocupants will be unharmed in the event of a fire. A table of roof fire ratings and details about the applicable standards is at FIRE RATINGS for ROOF SURFACES.
All roofing materials that carry any fire rating (A, B, or C) must:
Watch out: if a roofing shingle or other roof covering material is not installed exactly according to the manufacturer's recommendations its fire rating may be compromised and reduced, as may the roof warranty too. Also, a roof that has resisted a fire successfully, and thus helped protect the building from a fire, is likely to need to be replaced after a fire or after exposure to high heat from a nearby fire. Also watch for discount-grade roof shingles that may carry no fire rating whatsoever.
Also see these roofing material articles where we describe fire ratings:
Readers should also see ASPHALT SHINGLE FAILURE TYPES and Environmental Issues - Asbestos Roofing/Siding as well as SLATE ROOF DURABILITY and STAIN DIAGNOSIS on ROOFS, WARRANTIES for ROOF SHINGLES and WOOD SHAKE & SHINGLE ROOFING and finally WORKMANSHIP & WIND DAMAGE. For roofing material testing services and shingle testing see TEST LABS - ROOF SHINGLE.
- above section added DF. Continuing from from Best Practices Guide to Residential Construction:
Warranties for Asphalt Roof Shingles
Shingle warranties run from 20 to over 50 years. Although products with longer warranties are usually of higher quality, in some cases, the longer warranties are more of a marketing strategy than an accurate predictor of shingle life. While the specific terms of the warranty are important, more important is the manufacturer’s reputation for warranty service in the local area. All manufacturers retain the right to void the warranty if installation instructions are not closely followed, and they can often find a way to avoid honoring a claim if so inclined.
Details about roof shingle warranties are at
Details about the properties of asphalt roof shingles are found at Asphalt Shingle Properties.
Details about best practices in asphalt roof shingle installation are at ASPHALT SHINGLE INSTALLATION. Excerpts are below.
Installation Temperature Requirements for Asphalt Shingle Roofs
Ideally, shingles should be installed at temperatures ranging from 40°F to 85°F. Below 40°F, shingles are brittle and crack easily when hammered or bent. Above 85°F, it is easy to tear the shingles or mar the granular coating. In hot temperatures, roofers often start very early in the morning and break at midday. In cold temperatures, it is best to store the shingles in a heated enclosure until they are installed.
In cold climates, the sealant strip may not set up properly and may require manual sealing. For three-tab shingles, place two quarter-size spots of plastic roof cement under the lower corners of each tab (as shown in Figure 2-7). With laminated shingles, place four to six quarter-sized dots, spaced evenly, about one inch above the bottom of the overlapping shingle.
After the underlayment and drip edge are installed, a starter course of asphalt shingles, with the tabs removed, is nailed along the eaves so its sealant strip seals down the first course.
Successive courses are typically offset 6 inches (half a tab) on a 36-inch shingle in a stepped fashion, making cutouts align every other course and butt joints align every seventh course (Figure 2-8). For a more random pattern where cutouts align only every eighth course, offset shingles only five inches. Both of these patterns effectively resist leakage, but the 5-inch offset may provide longer wear since water will not be channeled down the cutouts thereby eroding the stone topping.
For ease of installation some roofers install shingles straight up the roof, staggering shingles 6 inches or 18 inches back and forth (Figure 2-9). Since this lines up butt joints every other course, this is considered a less watertight roof and may leak under extreme situations, such as windblown rain on a low pitch. It is not recommended by any roofing manufacturers. Manufacturers also claim that shingle color patterns may create splotches or stripes if laid this way.
The preferred fastener is galvanized roofing nails with a minimum 12-gauge shank and head diameter of at least 3/8 inch. Although staples are allowed in some jurisdictions, they do not provide the same holding power. Both nails and staples should be long enough to penetrate the roof sheathing by 3/4 inch or penetrate 1/4 inch through the sheathing if it is less than 3/4 inch thick. Fasteners should be driven straight and flush with the shingle surface (Figure 2-10). Overdriven nails or staples can cut into the shingle or crack it in cold weather.
Details about best practices in asphalt roof shingle installation are at ASPHALT SHINGLE INSTALLATION.
Details about valley flashing on asphalt shingle roofs are at ASPHALT SHINGLE VALLEY FLASHING. Excerpts are below.
Because valleys catch water rushing down two roof planes, they are likely places for roof leaks. Leaks can be caused by water rushing up the opposite side of the valley or from wear and tear caused by the channeled water, snow and ice buildup, or traffic on the roof. For that reason all valleys should start with a leakproof underlayment system to back up the shingle or metal valley detail.
Valley Underlayment Requirements for Asphalt Shingle Roofs
Start by cleaning any loose nails or other debris and nailing down any sheathing nails that are sticking up. If eaves flashing is used, it should cross the valley centerline each way and be installed before the valley underlayment (see “Eaves Flashing,” page 54 in the printed text Best Practices Guide to Residential Construction). Next install a 36-inch-wide strip of self-adhering bituminous membrane in 10- to 15-foot lengths up the valley.
Keep the membrane tight to the sheathing at the valley center, since any hollow sections could be easily punctured. Next install the 15-pound felt underlayment across the roof, lapping over the valley flashing by at least 6 inches. Roll roofing is also an acceptable underlayment for asphalt shingle valleys, although it is more prone to crack and is not self-healing around nails. After the underlayment is complete, the valley can be completed in any of the following ways (Table 2-3).
Details about valley flashing on asphalt shingle roofs are at ASPHALT SHINGLE VALLEY FLASHING.
Details about re-roofing options and best practices for asphalt shingle roofs are at ASPHALT SHINGLE RE-ROOF GUIDE, excerpts are below.
Reroofing saves the cost, trouble, and risks (water damage while the roof is exposed) associated with a tear-off. If the roof is structurally sound, most building codes allow for two layers of asphalt shingles and some allow for a third on roofs with a 5:12 or steeper pitch. If the original shingles are not badly curled and the sheathing is sound (check for bouncy areas), then a reroof is a good alternative.
Shingle Type Recommendations for Re-Roofing Asphalt Shingles
The heavier the shingle on the new layer, the less likely it is that irregularities in the surface below will telegraph through. Laminated or other heavy-textured shingles work well, as they do not need to be carefully fitted to the existing shingles, and the irregular texture will conceal any small bumps or dips from the original roof.
Clip any curled shingle corners and remove any curled tabs, replacing them with new shingle scraps as shims. Install new drip edge on rakes and eaves. Specialty drip edge profiles designed for retrofitting wrap around the exposed roof edge, leaving a neat protected edge. If the roof had no eaves flashing and one is needed, use a retrofit membrane such as AC Evenseal (NEI, Brentwood, New Hampshire).
Starter Course for Re-Roofing Asphalt Shingles
If laying three-tab shingles over threetab shingles, it is important to nest the new shingles against the old to create a flat surface. This process starts with a 5-inch starter strip fit along the eaves and set against the second course of existing shingles (see Figure 2-16).
Next install a course of shingles cut down to 10 inches wide, so they fit against the bottom edge of the existing third course (this creates a new 3-inch first course). After that, shingling should proceed normally, fitting each course up against the bottom of an existing course.
Fastening / Nailing Details When Re-Roofing with Asphalt Shingles
Use galvanized roofing nails long enough to fully penetrate the sheathing, typically 1 1/2 inches for a second roof and 1 3/4 inches for a third. Nesting each new row below an existing one keeps the new nails 2 inches below the existing, which will help minimize any splitting of the sheathing.
Flashings for Re-Roofing Asphalt Shingles
Depending on their condition and accessibility, some flashings can be reused. New shingles may be able to tuck under existing step flashing, chimney flashings, and front-wall flashings. If they are deteriorated, they must be replaced along with vent boots.
Valley Details for Re-Roofing Asphalt Shingles
Any type of valley flashing will work and simply lays over the existing flashing (except in a tear-off, where all flashings should be replaced). Unless a metal valley flashing is used, the first step is to line the existing valley with a new underlayment consisting of either 90-pound roll roofing or a more durable modified bitumen membrane. Then install either a closed or woven valley as described above.
Details about re-roofing options and best practices for asphalt shingle roofs are at ASPHALT SHINGLE RE-ROOF GUIDE.
Details about clay or concrete roofing tile selection, patterns, shapes, and installation specifications are at CLAY, CONCRETE, FIBER CEMENT TILE INSTALLATION. Excerpts are below.
Tile roofing accounts for about 8% of new residential roofs in the United States, primarily in the Southeast, Southwest, and on the West Coast. In addition to its durability and natural beauty, tile is impervious to fire, insects, and rot, and it can be formulated to withstand freeze-thaw cycles.
When colored white, tile roofing has been shown to reduce cooling costs by up to 22% for barrel or flat tile (compared to black asphalt shingles in tests conducted by the Florida Solar Energy Center). Since most tile roofs carry a 50-year warranty and a Class A fire rating, they are a popular choice for high-end projects, particularly in warm climates.
Nearly all roofing tiles in the United States were traditional clay until the 1960s when concrete tile first gained acceptance. Concrete tile now dominates most tile roofing markets, primarily due to its lower cost (see Table 2-4). Where weight is a concern, options include lightweight concrete tiles or fiber-cement shingles, which typically weigh even less. Fiber-cement roofing typically simulates slate or wood shakes and provides a Class A fire rating at a cost comparable to wood shakes.
Tile Shape Choices for Clay, Concrete, & Composite Tile Roofs
All tiles can be classified as high-profile, low-profile, or flat (see Figure 2-17). Common high-profile tiles include two-piece pan-and-cover Mission tile and one-piece Spanish S-tiles. Low profile styles include a wide variety, many with a double-S shape that creates multiple water courses. Many flat tiles are shaped and colored to simulate slate or wood shakes. In general, patterns using smaller tiles cost more per square for both materials and labor than patterns using larger tiles.
To make tiles, moist clay is extruded through a die or cast in a mold and then fired in a kiln until the clay “vitrifies,” fusing the particles together. Complete vitrification will create a strong tile with very low water absorption, which protects tile from freeze-thaw damage in cold climates or damage from salt air in coastal areas. Where regular freeze-thaw cycling is expected, roof tiles should comply with ASTM C1167 Grade 1, which allows minimal water absorption. Grade II tile provides moderate resistance to frost action, and Grade III tile is porous and should not be used in freeze-thaw areas.
When buying clay tile, look for at least a 50-year warranty on both durability and fading. Costs vary widely, depending on quality, style, and the shipping distance required. In general, patterns using smaller tiles will cost more for both materials and labor.
Color Choices for Clay Roof Tiles
Clay tiles come in a wide range of colors. Colorthrough tile takes the natural color of the clay, ranging from light tan to pink and red. Other colors can be added to the tile surface as a clay slurry before firing, but slurry coatings are only suitable for warm climates, as they cannot withstand freeze-thaw cycles. Clay tile can also be colored with ceramic glazes to create a durable, glass-like surface in just about any color. In general, clay tiles do not fade in the sun.
Blended Pattern Choices for Clay Roof Tiles
Some jobs require the installer to mix two or three different colors in a random pattern. The best way to achieve this is to premix bundles on the ground with the correct proportion of each color, then send them up to the roof for installation. Periodically inspect the roof from the ground for hot spots or streaking.
Clay Roof Tile Styles
Clay roof tiles are available in traditional two-piece styles, one-piece profiles, and flat profiles (Figure 2-18).
Designs are either overlapping or interlocking, with protruding lips that lock the tiles together and form a weather seal. Many flat clay tiles interlock. Interlocking designs are recommended for regions with heavy rain or snow. Manufacturers provide special trim tiles to seal the voids formed at ridges, rakes, and hips.
Concrete tiles were introduced to the United States in the early 1900s, but they did not catch on until the 1960s. They now account for more than half the tiles sold in the United States. In Europe, over 90% of new houses have concrete tile roofs. Concrete tiles cost as little as half as much as clay and offer both traditional and flat styles that simulate slate roofing and wood shakes.
High-quality concrete tiles should last up to 50 years in arid climates and up to 30 years in hot, humid climates. While some early products faced problems with freeze-thaw cycling, most newer formulations are made to withstand winter weather. In cold climates, make sure the product is warranted for freeze-thaw durability.
Special lightweight concrete tiles weighing under 600 lb per square are gaining in popularity. Although they cost more than standard concrete tiles and are more prone to breakage, they are easier to handle and suitable for applications where the roof structure cannot support the weight of standard tiles. Lightweight tiles cannot support foot traffic without adding walking pads to distribute weight or filling the space under the tiles with polyurethane foam. They are also not recommended for high-snow regions.
Color Choices in Concrete Roofing Tiles
Concrete tiles can be surface colored with a slurry of iron-oxide pigments applied to the surface or have the color added to the concrete mix for a more durable, and expensive, through-color. Through-color choices are more limited, and the colors are more subdued. Either type of tile is also sealed with a clear acrylic spray to help with curing and efflorescence. While the color-through tile will hold its color better than the slurry type, particularly under freeze-thaw cycling, all concrete tile coloring can be expected to fade and soften over time. Surface textures can also be added to flat concrete tiles to simulate wood shakes or shingles.
Concrete Roof Tile Styles
Concrete tiles are available in shapes that simulate traditional clay styles as well as flat profiles that simulate wood or slate (Figure 2-19). Most are designed with an interlocking channel on the left edge that is lapped by the next tile. Underneath each tile is a head lug at the top and series of ridges at the bottom. The head lug fits over the top of a horizontal 1x batten, if these are used.
Otherwise it sits directly on the roof deck. The ridges at the bottom (called nose lugs or weather checks) match the profile of the tile below, creating a barrier against windblown rain and snow. Manufacturers provide special trim tiles to fill in the large voids that profile tiles leave at ridges, rakes, and hips. While many sizes are available, the most common concrete tiles measure 12 to 13 inches wide by 16 1/2 or 17 inches long.
Concrete Spanish S-tile. These provide the look of traditional two-piece Mission tiles but with simpler installation. Nearly all have interlocking side channels.
Interlocking low-profile concrete roof tile. These have a less pronounced double-S shape and interlocking joints and side channels. Heads and butts may also interlock or simply overlap.
Interlocking flat concrete roof tile. These simulate clay roof tiles, wood shakes, and slate. Ridges, hips, and rakes are easier to seal than with curved tiles.
Early generations of fiber-cement roofing products using asbestos fibers were used successfully in the United States for over 50 years.
Newer formulations introduced in the 1980s and 1990s used wood fibers instead of asbestos and were marketed widely in the western United States as a fire-resistant alternative to wood shakes. Made from a mixture of Portland cement and wood fibers, they weighed 400 to 600 pounds per square and were designed to imitate slates or wood shakes. They promised excellent resistance to insects, fungus, fire, and weathering and carried warranties ranging from 25 to 50 years.
Performance Problems of Fiber Cement Roofing Tiles
Within five years of installation, however, many of the fiber-cement shakes began to deteriorate. Problems included surface crazing, cracking, delamination, and softening and resulted in a number of lawsuits against key manufacturers and several companies abandoning the product. The problems were generally linked to high water absorption, which created an alkaline solution that was corrosive to the wood fibers.
Some products have fared better than others. In general, products that are steam-cured in an autoclave will have lower water absorption, but they tend to be more brittle. Many products are represented as complying with ASTM C1225, a standard for nonasbestos fiber-cement roofing shingles; but in its current form, this standard does not guarantee long-term durability.
Watch out: Only a product with a proven long-term track record in a specific climate zone should be considered.
Details about clay tile roof slope requirements, roof sheathing, and roof underlayment are at CLAY TILE ROOF SLOPE, DECK & UNDERLAY. Excerpts are below.
Roof Slope Requirements for Tiled Roofs
Most manufacturers recommend minimum slope requirements for their tiles as well as special underlayment and fastening techniques for low-slope installations. Typical minimums are shown in Table 2-5. Some manufacturers allow specific tile types to be installed on roofs as shallow as 2 1/2 :12 if a full waterproofing layer, such as a built-up roof or single-ply membrane, is installed.
Reduced exposure and special fastening techniques may also be required for low slopes. On slopes less than 3 1/2 :12, roofing tile is considered decorative only. The underlying roof provides all the necessary waterproofing.
In general, there is no maximum slope for tile roofs. However, on extremely steep roofs above 19:12 or on vertical applications, wind currents may cause tiles to rattle. To avoid this, use wind clips on each tile along with a construction grade silicone sealant or other approved sealant.
Roof Sheathing Requirements for Tiled Roofs
While spaced sheathing is allowed under the codes, most installations today are done on solid wood sheathing with or without battens. The sheathing must be strong enough to support the required loads between rafters. Minimum requirements are nominal 1 inch for board sheathing or 15/32 for plywood and other approved panel products.
Underlayment Requirements for Tiled Roofs
Because of the long service life of tile, a long-lasting underlayment should be used as well. Underlayments play a key role in tile roofing, since most tile roofs are not completely waterproof. At a minimum, use a Type II No. 30 or No. 43 felt, lapped 2 inches on horizontal joints and 6 inches at end laps. The underlayment should lap over hips and ridges 12 inches in each direction and turn up vertical surfaces a minimum of 4 inches (Figure 2-20).
At tricky areas, such as around roof vents, chimneys, and skylights, self-adhesive bituminous membrane can help achieve a watertight seal. In windy areas, use tin caps or round cap nails to hold the underlayment securely. The fastening schedule for the underlayment will depend on local wind conditions.
For harsher conditions or shallower slopes, use mineralsurface roll roofing, self-adhering bituminous membrane, or other durable waterproofing systems. For slopes below 3-1/2:12 the underlayment must provide complete weather protection, and the tiles are considered merely decorative. Underlayment recommendations for different types of tiles and climate conditions are shown in Table 2-6, Table 2-7, and Table 2-8.
Details about clay tile roof slope requirements, roof sheathing, and roof underlayment are at CLAY TILE ROOF SLOPE, DECK & UNDERLAY.
Details about preparing a roof for clay tile installation incude installation of battens and stacking clay tiles properly on the roof for later layout and fastening: this information is found at CLAY TILE ROOF BATTENS & STACKING. Excerpts are below.
Batten Specifications for Tiled Roofs
Tiles with projecting head lugs can be installed either directly on the deck or with the lugs fitting over pressure-treated wooden battens nailed horizontally across the roof. Battens are typically nominal 1x2 or 1x4 lumber, but they may be larger to accommodate snow loads or unsupported spans over counterbattens. Battens should be made from pressure-treated lumber except in very dry climates.
They are nailed at minimum 24 inches on-center with spaces for drainage every 48 inches. Lay out battens to provide equal courses with a minimum 3-inch head-lap, unless the tile profile is designed for a specific head-lap. Fasten with 8d galvanized nails or corrosion-resistant 1 1/2-inch 16-gauge staples with 7/16-inch crowns.
Battens are recommended on roof slopes greater than 7:12 to provide solid anchoring and on slopes below 3:12 to minimize penetration of the underlayment. On low slopes and in areas subject to ice damming, counterbattens nailed vertically up the roof slope are also recommended to promote drainage.
Counterbattens should be minimum 1/4 x 2 inches thick in moderate climates, 3/4 inch thick in areas subject to ice damming. When battens are nailed directly to the deck, allow a 1/2 -inch gap every 4 feet or set the battens on minimum 1/4 -inch shims placed at each nail (see Figure 2-21).
Layout and Stacking Specifications for Tiled Roofs
Lay out the courses so that tile exposures are equal with a head-lap of at least 3 inches (unless the tile specifies a different lap). Snap lines on the underlayment along the top of each course or along each batten. One or more vertical lines can also be helpful in keeping the tiles aligned. Accurate layout is critical with most tile patterns.
Next, carry tiles up to the roof and distribute the weight equally across the roof, as tiles weigh as much as 10 pounds each. Depending on the tile, stacks of about 6 to 10 tiles is workable. If mixing different colored tiles, arrange bundles with the correct proportions on the ground before stacking them on the roof.
Details about preparing a roof for clay tile installation incude installation of battens and stacking clay tiles properly on the roof for later layout and fastening: this information is found at CLAY TILE ROOF BATTENS & STACKING.
The preferred method of attachment depends on the type of tile, climate conditions, and slope of the roof.
Loose Laid Tile Roofs
For standard concrete tiles with lugs set on battens, building codes still allow tiles to be laid loose at slopes less than 5:12 (except for one nail per tile within 36 inches of hips, ridges, eaves, or rakes). Loose-laid tiles are not allowed, however, in snow regions, areas subject to high winds, or with tiles weighing less than 9 pounds per square foot installed.
Nail on Tile Roofs
Nails are the least expensive and most common method for attaching concrete and clay tiles. Tiles can be nailed either directly into the roof sheathing or tiles with lugs can be nailed to battens. Corrosion-resistant nails must be minimum 11 gauge, with 5/16 -inch heads, and long enough to penetrate the sheathing by 3/4 inch—typically 8d nails.
Ring-shank nails or hot-dipped galvanized nails hold better than smooth-shank nails in areas subject to heavy winds. Whether driven by hand or pneumatic nailers, nails should be driven so heads lightly touch the tile but not so tight as to risk cracking tiles. Because of the longevity of a tile roof, some contractors use copper or stainless-steel roofing nails. No. 8 or 9 stainless-steel or brass screws also work well and are sometimes used in high-wind regions.
Most tiles have two prepunched nail holes. On curved tiles, use the hole closest to the deck surface unless a nail there would penetrate a critical flashing. The other hole is also used for cut tiles or applications requiring two nails. For example, all flat, noninterlocking tiles require two nails. And in snow regions, codes require two nails per tile for all types and slopes. Otherwise follow the guidelines in Table 2-9, or the manufacturer’s guidelines if they are more stringent.
Details about fastening clay tiles to roofs are at CLAY TILE ROOF CONNECTIONS.
Details about connector requirements for clay or concrete roof tiles in high wind, hurricane, or seismic areas are provided at CLAY TILE WIND & SEISMIC CONNECTORS. Excerpts are below.
In areas prone to high winds, such as Florida, setting the tiles in mortar was once considered the strongest system. However, newer anchoring systems using wires, special clips, and, in some cases, specialized adhesives have proven more reliable and have replaced mortar-set systems as the preferred approach. Wire and clip systems also perform better than rigid attachment systems in seismic zones, as the flexible systems tend to absorb the shockwaves of an earthquake and protect the tiles from cracking.
Building codes vary in their requirements for high-wind and seismic areas but most permit one or more of the anchoring systems described below. Model specifications for high-wind installations are available in the Concrete and Clay Roof Tile Installation Manual, jointly published by the Florida Roofing, Sheet Metal and Air Conditioning Contractors Association and the Tile Roofing Institute. General guidelines for high-wind installations or roofs over 40 feet above grade include:
Twisted Wire Requirements for Tile Roof Installations
This approach is used on roofs ranging from 2:12 to 24:12 in seismic zones and areas with moderate winds. Rather than nail the tiles to the roof, each tile is wired to a length of twisted 12-gauge wire (galvanized, copper, or stainless steel) running from eaves to ridge under each vertical course of tiles. The twisted wire has a loop to tie into every 6 inches and is attached every 10 feet with special anchors, making relatively few holes in the underlayment (see Figure 2-22).
Because wire systems allow some movement, seismic forces do not tend to break the tiles. Also, damaged tiles are easy to replace by snipping the tie wire and wiring in a new tile. Installation is labor-intensive, however, compared to nailing.
Hurricane Clip Requirements for Tile Roof Installations
A hurricane clip, also known as a storm clip or side clip, is a concealed L-shaped metal strap designed to lock down the water-channel side of a roofing tile near the nose (Figure 2-23).
Clips are well-suited to concrete tile and are used in conjunction with nails, screws, or other systems that secure the head of the tile. They are approved for use in some hurricane areas, but they should be combined with a nose clip or similar device for maximum protection. Used alone, they may deform or loosen after several storms.
Nose Clip Requirements for Tile Roof Installations
Also known as nose hooks, butt hooks, or wind locks, these simple metal clips hold down the bottom (nose) end of a roofing tile to prevent strong winds from lifting and breaking the tiles (Figure 2-24).
Nose clips are nailed in place through the underlying tile or attached to the tie wires in wire systems. They are compatible with all methods of tile attachment and are recommended for high-wind areas and slopes greater than 7:12. The main drawback to nose clips is that they are visible at the nose of each tile, which some homeowners find objectionable.
Tile Nail Option for Tile Roof Installations
This innovative fastener, used mostly with S-tile or two-piece Mission tile, functions as both a nail and a nose clip. Because the nail is driven about 6 inches above the tile, there is no risk of breakage and the nail hole can be easily sealed with mastic (Figure 2-25).
Tile nails are approved for all slopes and are especially useful in high-wind areas and on very steep pitches such as mansards. They are also useful for securing the first course of two-piece Mission tile. Examples include the Tyle Tye® tile nail from Newport Tool & Fastener Co. and the Hook Nail from Wire Works, Inc.
Tile Adhesives Option for Tile Roof Installations
Another way to prevent uplift in windy conditions and to keep tiles from rattling on steep slopes is to set the butt edge of each tile in a dab of roofing cement. Over time, however, roofing cement may become brittle and fail. New proprietary tile adhesives promise to last longer and stay flexible over time. In hurricane-prone areas, some contractors are applying adhesive to every tile—in some cases combined with other fastening methods, such as twisted wires. While long-term performance has not been well-established, testing by manufacturers has demonstrated that adhesives can outperform mortar systems in hurricane-force winds.
Details about connector requirements for clay or concrete roof tiles in high wind, hurricane, or seismic areas are provided at CLAY TILE WIND & SEISMIC CONNECTORS.
Details about proper closure or installation of eaves, hip, and rakes on clay tile roofs are provided at CLAY TILE EAVES, HIP & RAKE DETAILS. Excerpts are below.
Eaves Closure Requirements on Tile Roofs
Both profile and flat tile need special treatment at the eaves to raise the bottom edge of the first tile to the correct height and to close off any openings to birds and insects. For profile tile, many contractors use a metal birdstop, a preformed L-shaped strip with the vertical leg cut to match the underside of the first tile and fit snugly between the weather checks (see Figure 2-28).
With some high-profile tiles, a special eaves-closure tile achieves the same effect as shown in Figure 2-26.
With flat tiles, the first course may be raised with a special starter tile, as shown in Figure 2-27, or by a metal eaves closure, raised fascia, or wood cant strip. With a cant strip or raised fascia, a beveled wood or foam antiponding strip is required to prevent ponding of water along the eaves (Figure 2-29).
Ridge and Hip Requirements on Tile Roofs
Unless hip and ridge tiles are going to be set into a continuous bed of mortar, special nailers are required to install them. The hip and ridge boards are typically 2x3s to 2x6s set on edge to hold the trim tiles in an even plane. They are toenailed in place and individually wrapped with felt (Figure 2-30).
Hip and ridge tiles are later nailed on with a 2-inch head-lap, and the lower ends are sealed at the overlap with roofing cement or an approved tile adhesive. Finally, mortar, special trim tiles, or other weatherblocking is applied to fill in gaps between the ridge and hip tiles and the field tile.
Rake Requirements on Tile Roofs
Details about proper closure or installation of eaves, hip, and rakes on clay tile roofs are provided at CLAY TILE EAVES, HIP & RAKE DETAILS.
Details about flashing specifications for tile roofs are at FLASHING, CLAY TILE ROOFS. Excerpts are below.
Because of the longevity of a tile roof, high-quality flashing materials should be used. The International Residential Code calls for a minimum 26-gauge metal. Galvanized steel should have a minimum of 0.90 ounces of zinc per square foot (G90 sheet metal). More expensive options include prepainted galvanized steel or 16-ounce sheet copper.
Tile Roof Details Recommended at Openings and Walls
At walls, dormers, chimneys, and other vertical surfaces, extend the flashing up at least 6 inches and counterflash. Extend flashing under the tile a minimum of 6 inches or as specified by the tile manufacturer. With flat shingles, use step flashing with a minimum 6-inch vertical leg and 5-inch horizontal leg with a hemmed edge. Profile tile along a wall should receive channel flashing turned up at least one inch on the lower flange (Figure 2-32).
Pipe Flashing Requirements on Tile Roofs
Pipe flashings generally get both a primary flashing when the underlayment is installed and a secondary soft-metal underlayment that conforms to the tile. For profile tile, this can be 2 1/2 -pound lead or dead-soft aluminum with an 18-inch-wide skirt (Figure 2-33).
Valley Details for Tile Roofs
According to the International Residential Code (IRC), valley flashing in tile roofs should extend at least 11 inches each way from the valley centerline, and the flashing should have a formed splash diverter at the center at least one inch high. The code requires a minimum underlayment at the valley of 36-inch-wide Type I No. 30 felt in addition to the underlayment for the general roof areas. In cold climates (average January temperature of 25°F or less), a self-adhering bituminous underlayment is recommended. Battens, if used, should stop short of the valley metal.
Tiles along the valley edge may be laid first and cut in place along a chalked line. Cut pieces are attached by roofing cement or a code-approved adhesive, or they may use wire ties, tile clips, or batten extenders.
Open Valley Details on Tile Roofs
Open valleys permit free drainage and are recommended in areas where leaves, pine needles, and other debris are likely to fall on the roof. They are also recommended in areas subject to snow and ice buildup.
The valley flashing should have hemmed edges and be installed with cleats that allow individual sections to expand and contract (Figure 2-34).
Closed Valley Details on Tile Roofs
In this type of valley, the flashing carries the runoff and the tile in the valley is only decorative. These are not recommended where debris from trees may fall on the roof or where the two roof planes joining at the valley have different pitches or length, causing uneven flows.
Foot Traffic Advice for Walking on Tile Roofs
To prevent breakage, walk on tiles with extreme caution. Profile tile and lightweight tile are the most vulnerable, and concrete tiles are more fragile when they are freshly manufactured or “green.” If possible, place antennas and other roof-mounted equipment where it is easy to access without crossing many tiles. When it is necessary to walk on tiles, step only on the head-lap (lower 3 inches) of each tile. With Mission- or S-tiles, it is best to step across two tiles at once to distribute the weight. When significant rooftop work is required, place plywood over the tile to distribute the load.
Tips for Replacing Broken Roof Tiles
If a tile is cracked, gently lift the overlapping tile and wiggle loose the damaged tile. Remove the tile nail, screw, or clip with a slate ripper or hacksaw blade. Seal any nail holes with roofing cement and slip a new tile into place, securing the butt end with an L-hook or bent copper wire (as shown in Figure 2-35).
Details about flashing specifications for tile roofs are at FLASHING, CLAY TILE ROOFS.
Details about types of metal roofing are found at our metal roofing home page, METAL ROOFING. Excerpts are below.
Residential installations of metal roofing have more than doubled in the past several years, and they are now estimated to account for over 10% of residential roofs. Originally associated with agricultural and commercial buildings, new metal roofing products aimed at the residential market are designed with simplified installation systems and offer more choices in materials, finishes, and design. The installed cost of premium metal roofing is three to four times more than asphalt shingles, but metal roofing offers a variety of attractive benefits:
There are three general types of residential metal roofing: Exposed-fastener panels, standing-seam, and modular panels.
Details about types of metal roofing are found at our metal roofing home page, METAL ROOFING.
Details about exposed-fastener panel metal roofs, also referred to as "barn roofing" are at METAL ROOF EXPOSED FASTENER SYSTEM. Excerpts are below.
Steel and aluminum panel roofing with exposed fasteners has been a popular choice on agricultural buildings for decades. In recent years, these “ag panels” have grown increasingly popular for rural homes as well, since they can provide a long-lasting roof at a cost comparable to asphalt shingles. The products installed on homes, while essentially the same material as the agricultural panels, generally use better metal coatings, and installers pay more attention to sealing and watertight detailing.
While a carefully installed exposed-fastener roof should be free of leaks upon completion, small installation errors can result in leakage later as the metal panels undergo normal thermal movement that places stress on the fasteners. With so many exposed holes in the panels, periodic inspections are recommended. Also, the exposed fastener heads, in addition to lending a rural look to the building, tend to catch leaf debris and restrain sliding snow.
Materials used in Exposed-Fastener Metal Roofs
Exposed-fastener panels are typically 26 to 29 gauge, compared to the heavier 22 to 26 gauge used in standing-seam roofing. The ribs in exposed fastener roofing are also lower and closer together than in standingseam roofing and may be squared, rounded, or v-shaped (see Figure 2-36). Most panels are 2 to 3 feet wide and formed with galvanized steel, Galvalume®, or aluminum.
Panel length. While some stock sizes are available, ordering panels factory-cut to exact lengths simplifies installation and reduces corrosion at field cuts. Panels can be ordered in any shippable length, although excessive thermal movement can be a problem for steel panels longer than 40 feet or for aluminum panels longer than 16 feet. In regions with very wide temperature swings, contractors should use shorter lengths (see “Thermal Expansion” in Table 2-10, or on page 83 in the printed text Best Practices Guide to Residential Construction).
Installation Methods for Exposed-Fastener Metal Roofs
While traditionally installed over battens, most panels in residential installations are now installed over a solid plywood deck with minimum No. 30 felt underlayment. Metal roofing manufacturers recommend plywood over oriented-strand board (OSB) due to plywood’s better screw-holding ability. Roofing felt should be installed with plastic cap nails rather than metal buttons, which can deteriorate the metal roofing by galvanic action (see “The Galvanic Scale,” page 83 in the printed text Best Practices Guide to Residential Construction).
Align the metal roof panel to eaves. After installing drip edges and valley flashing, the first panel is fit along one rake, square to the bottom edge of the roof. If the roof is not square, the first panel may need to be cut at a bevel along the rake. Start at the downwind end of the roof, so the edge of each overlapping panel faces away from the prevailing winds.
Cutting exposed fastener metal roof panels. Where panels need to be cut, use snips or shears rather than an abrasive blade, which overheats the steel coatings and leaves a rough edge prone to rust. Abrasive blades also produce hot metal filings that can embed in the paint and cause rust on the face of the panels.
Side and end laps on exposed fastener metal roofs. After the first panel is screwed down, the next panel is set in place, lapping over the first. Side laps are typically sealed with butyl tape and held together with gasketed sheet-metal screws. Where more than one panel is used up the run of the roof, the upper panel laps the lower by 6 inches and is sealed with butyl tape.
Fasteners used on exposed-fastener metal roofs. Fasteners are typically special wood screws with integral EPDM or neoprene gaskets that compress under the screw head to seal the hole. Fasteners should be driven at a right angle to the roof plane and should be snug but not so tight as to deform the washer (see Figure 2-37). Nearly all manufacturers recommend placing screws in the flat sections between ribs.
Although making holes in the flat section may seem unwise, placing screws in the ribs is discouraged for two reasons. First, the long exposed screw shaft passing through the rib is prone to snap over time due to thermal movement of the panels. Second, it is easy to overdrive the screws and crush the panels. Higher-cost EPDM washers are less likely to leak than neoprene.
Reroofing Using Exposed Fastener Metal Roof Panels
Panels can go directly over a single layer of asphalt shingles in good condition. If the shingles are curled or uneven, install 2x horizontal purlins at 16 inches on-center. In either case, put down a new layer of No. 30 underlayment before installing the panels.
Details about exposed-fastener panel metal roofs, also referred to as "barn roofing" are at METAL ROOF EXPOSED FASTENER SYSTEM.
Details about flashing and accessories for exposed-fastener metal roof systems are at METAL ROOF EXPOSED FASTENER FLASHING. Excerpts are below.
Most manufacturers supply preformed flashings, drip edges, rake moldings, and ridge caps color-matched to their roofing panels, as well as color-matched coil stock for fabricating custom pieces onsite. They also provide rubber closure strips or expandable foam tapes to seal panel ends against water and insect intrusion at eaves, valleys, ridges, and other terminations.
Pay particular attention to panel ends at valleys. Some manufacturers supply special closures for the angled cuts through ribs, but closures may need to be fashioned by cutting up standard closure strips. Some manufacturers also provide an expandable foam sealant tape that conforms to the rib pattern for a tight seal up the valley.
Depending on the panel profile, the end treatment will vary, but ends should be fully sealed. Remember to place screws in flat sections and to use extra screws up the valley (Figure 2-38). For a vented ridge, place short sections of a matrix-type ridge vent between the ribs and secure with a preformed metal cap (Figure 2-39).
For plumbing vents, most manufacturers recommend a moldable aluminum jack bent to conform to the profile of the roofing (Figure 2-40).
Rectangular openings, such as skylights and chimneys, typically require both base and counterflashing so roof panels are free to move with changes in temperature.
Depending on the panel profile, either use a pan flashing or an L-flashing sealed to the top surface of the roofing panel with sheet metal screws and butyl tape.
On large openings, a cricket is needed on the upslope to divert water around the penetration. Custom-made, one-piece curbs with built-in diverters simplify this type of installation. All flashing joints should be sealed with butyl tape or a manufacturer- recommended sealant.
Sealing Details for Exposed-Fastener Metal Roofs
For the watertight performance required on homes (as opposed to barns), metal roofs need careful sealing around all penetrations, side laps, and end laps. On side seams and lap joints, the sealant should always go on the uphill, or “dry,” side of any fasteners (Figure 2-41). Sealant should also be used at ridge caps, valleys, and wherever flashings lap over or under the metal roofing.
The preferred sealant for most concealed seams in roof panels is butyl tape, which absorbs movement and will not shrink. Gunnable terpolymer butyl or urethane caulk can also be used, as specified by the manufacturer. But never use acid-cure silicone caulking (the common type with vinegar odor) or asphalt roofing cement, as they will damage most metal coatings.
How to Allow for Panel Movement in Exposed Fastener Metal Roof Systems
Metal panels were originally designed for installation on purlins that can absorb the normal movement as the panels expand and contract from temperature changes. The thermal movement of a long panel installed over solid plywood, however, can cause problems.
Typically, either the hole in the roofing elongates—creating a potential leak—or the screw becomes loosened, making the roof vulnerable to blow-off. The problems are greatest with aluminum, which has 70% more thermal movement than steel and less tensile strength. To avoid problems, experts recommend the following:
Wavy Metal Panels or Oil-Canning Problems on Metal Roofs: Thermal Expansion
Thermal expansion in light-gauge metal panels can cause a wavy appearance called “oil-canning” in the flat areas. In general, this does not signal a performance problem, but it may be visually objectionable. Oilcanning tends to be most visible in bright light from a close distance, and it is generally more noticeable on shiny metals, such as Galvalume®, than on colored metal panels. It is primarily a problem in profiles with few ridges to stiffen the panels. To reduce the effect, some manufacturers provide self-adhesive foam strips that are attached lengthwise to the bottom of metal panels.
Details about flashing and accessories for exposed-fastener metal roof systems are at METAL ROOF EXPOSED FASTENER FLASHING.
see STANDING SEAM METAL ROOF INSTALLATION for details about standing seam roof installation, flashing, maintenance, repair.
Standing-seam roofing consists of individual panels that run the length of the roof with a high rib up each side of the panels. The ribs overlap and lock together, concealing the fasteners and giving the roofing its name. The hidden fasteners allow thermal movement in the panels and are less likely to leak than exposed fasteners. However, some trim pieces are still fastened with exposed screws.
The smooth surface of a standing-seam roof provides a cleaner appearance and is easier to keep clear of leaf debris than tile, wood, or other textured roofing surfaces. Also, it can be walked on when necessary. Snow slides off easily as well, making this a popular choice in high snow regions. The cost is generally 25% to 50% more than an exposed-fastener roof of similar materials.
Materials Used in Standing Seam Metal Roofs
Standing-seam panels are 8 to 24 inches wide and available in steel, copper, and aluminum with a wide array of finishes (discussed below). Stiffening ribs may be added to wider panels to reduce waviness (oil-canning). Thicknesses for quality residential applications are typically 24 or 26 gauge, but lighter and heavier stock is also available. Installers can form panels on-site from coil stock with portable roll-forming equipment, or they can order factory-made panels from a growing number of metal roofing manufacturers. Most factory-made panels have snaptogether seams, eliminating the need for special crimping equipment used by site fabricators. In most cases, panels are fabricated to run from eaves to ridge, eliminated the need for end lap joints.
Installation Specifications for Standing Seam Metal Roofs
On new homes, most panels are installed over a solid plywood deck with minimum No. 30 felt underlayment. Metal roofing manufacturers recommend plywood rather than OSB due to plywood’s better screwholding ability. Install the felt with plastic cap nails rather than metal buttons, which can cause corrosion when in contact with the roofing panels (see GALVANIC SCALE & METAL CORROSION).
After installing the drip edge, install the first panel, making sure it is square to the bottom edge of the roof. If the roof is not square, pull the panel away from the rake so the first rib does not overhang the rake edge. Later, the rake trim piece will cover any small discrepancies. If the panels have an integral screw flange, keep the screws just snug so the panels can move with temperature changes. The clips are designed to allow thermal movement.
The next panel fits over the first with an overlapping rib. Fit each panel to a line snapped up the roof, marking the edge of each panel. Without layout lines, the panels can build up an incremental error, throwing off the layout. As panels are installed and secured, the joints are easily locked together with hand pressure. Traditional standingseam roofing required special motorized crimpers to lock the seams. While these are still used on some low-slope systems, most residential installations now use snap-together panels. Unless the layout works perfectly, the last panel will need to be cut along the opposite rake and bent with a hand seamer to form the end rib.
Reroofing Using Standing Seam Metal Roofs Over Other Roof Coverings?
Many installers will not install standing-seam roofing over existing asphalt shingles since the rough surface will tend to bind the panels and cause “oil-canning,” as the panels move with temperature changes. One option is to install the new metal roofing over 2x4 purlins nailed through the old roofing and shimmed to form an even plane. Follow manufacturer’s recommendations for spacing of purlins, typically no more than 24 inches on-center.
Flashing and Sealing Details for Standing Seam Metal Roofs
Manufacturers of preformed roofing panels provide eaves and rake flashings, ridge caps, and sidewall flashings in matching finishes, as well as coil stock for site fabrication. Many flashings are designed with hidden fasteners; others require exposed gasketed screws. Typical details are similar to those found in Figure 2-41. Follow manufacturers’ recommendations regarding which sealants to use for compatibility with the roofing (typically butyl tape, or gunnable terpolymer butyl or urethane sealant). In general, avoid acid-cure silicone (the type that smells like vinegar) as it can be corrosive to many metal finishes.
Details about modular metal roofing shingles are at MODULAR METAL ROOF SHINGLE SYSTEM. Excerpts are below.
Modular metal shingles comprise the fastest growing segment of the metal roofing industry. Using light-gauge steel, copper, or aluminum, panels are stamped to imitate slates, shakes, asphalt shingles, or tiles. Some have aggregate stone finishes that closely resemble asphalt shingles. Most carry warranties from 20 to 30 years against fading and from 50-year to “lifetime” warranties against cracking or delamination of the shingle itself.
Modular shingles carry a Class A or B fire rating, depending on the material and installation details, and are highly resistant to wind uplift and damage from hail. Installed prices range from two to three times the cost of premium asphalt shingles. Installers accustomed to asphalt shingles or tile should have little trouble adjusting to metal shingles.
Materials Used in Modular Metal Roof Shingle Systems
Modular shingles are typically stamped from lightweight .0165-inch metal, which is thinner than other types of metal roofing but stiffened by the textured patterns. Typical rectangular panel sizes range from 24 to 48 inches long by 12 to 16 inches wide, but they also include tile and diamond shapes and other specialty patterns. Weights range from 40 pounds per square for aluminum shingles to 140 pounds per square for steel shingles with a heavy stone aggregate. The lightweight patterns are wellsuited to reroofing where weight is a concern. Most panels can be walked on, if done with care, but areas with heavy foot traffic should be reinforced with foam backers provided by the manufacturer.
Installation Methods for Modular Metal Roof Shingle Systems
Modular shingles are either nailed directly to the wood deck or attached to 2x2-inch battens installed at the exposed panel width, usually about 15 inches. Installation on battens allows more deeply etched patterns, such as simulated tiles. Either type can be installed with pneumatic nailers.
Underlayment is minimum No. 30 asphalt felt held with plastic caps to avoid contact between incompatible metals. Many manufacturers recommend proprietary laminated underlayments, such as VersaShield (Elk Premium Building Products, Inc.), which are tougher and less slippery than felt and provide better fire ratings. Aluminum shingles require fire-resistant underlayments to achieve an A or B fire rating.
Direct to deck Modular Metal Roof Shingle Method: Shingle panels installed directly to the deck are attached with concealed nails, either through clips or a nailing flange along the top, and have interlocking edges along all four sides (Figure 2-43). As they are installed, each panel locks to the panel below and to the left.
Modular Metal Roof Shingle Over battens: Modular panels designed for installation on battens have a nailing flange along the bottom of each shingle panel with nails going horizontally into the batten (Figure 2-44). Battens are useful for retrofits where the surface is irregular. Also, the air space boosts energy savings, especially when using shingles with solar-reflective surfaces.
Both systems begin with the installation of a drip edge and gable trim designed for the specific system. Working from left to right, the first shingle panel hooks into the drip edge, which also serves as a starter strip. Successive courses are staggered as specified by the manufacturer.
Reroofing Using Modular Shingles On Top of Other Roof Coverings
In general, most modular shingles can be installed over existing asphalt shingles if they are in good condition without excessive curling and deformation. Shingles designed to go over battens have more flexibility, since the battens can be shimmed to create a level surface.
Flashing and Sealing Details for Modular Metal Roof Shingles
Manufacturers provide standard flashings similar to those for standing-seam products. Eaves and rake flashings typically have concealed fasteners and lock the shingles in place. Ridge and headwall flashings often require exposed fasteners. Depending on the shingle profile, sidewall, chimney, and skylight flashings are either pan or step flashings. Typical details are shown in Figure 2-45.
Details about modular metal roofing shingles are at MODULAR METAL ROOF SHINGLE SYSTEM.
Details about the various metals used in roofing are at METALS USED IN ROOFING and at A Complete List of Types & Properties of Metal Used in Roof Systems. Excerpts are below.
While some companies offer roofing products in copper, zinc, and stainless steel, the vast majority are coated steel and aluminum. Coated steel products are the most common and least expensive. In its favor, steel moves relatively little with temperature changes, has good structural characteristics, and resists denting. Its high melting point gives it a Class A fire rating. All coated steel materials, however, are vulnerable to corrosion at field-cut edges— although Galvalume® is the least affected (Table 2-10).
Galvanized Steel Metal Roofing System Properties
To protect against corrosion, the steel is bonded to a layer of zinc, which works as a sacrificial coating on the surface and also offers some protection to cut edges and nicks by flowing to these areas. The heavier the zinc coating, the longer the protection. The Metal Roofing Alliance recommends G-90 galvanized steel for roofing, which has 90 ounces of zinc per square foot.
Unpainted G-90 galvanized steel is typically warranted against corrosion for 20 years under normal conditions. It often lasts longer, but it may show visible corrosion in as few five years under harsh conditions, such as salt spray, significant air pollution, or low-slope applications in wet climates. Field cuts made with an abrasive saw are prone to corrosion.
Aluminized Steel Metal Roofing System Properties
Developed in the 1950s, this is similar to galvanized steel, but it uses aluminum as the coating instead of zinc. The aluminum provides a physical barrier against corrosion and creates a reflective surface that helps reduce heat transfer to attics. However, aluminum does not have the self-healing properties of zinc, so exposed edges and scratches are more susceptible to rust. Aluminized steel generally outlasts galvanized steel but has largely been replaced in the market by Galvalume®.
Galvalume Metal Roofing System Properties
Also sold under the tradenames Zincalume ® and Galval®, Galvalume® was developed in the early 1970s. The underlying steel is coated with a zincaluminum alloy that combines the long-lasting protection of aluminum with the self-healing properties of zinc. It also has the reflective qualities of aluminum, reducing attic temperatures and cooling loads. The most common application weight is AZ 55, which has about a 1-mil-thick coating on each side. Unpainted Galvalume® is warranted against corrosion for 20 years, but it has stood up well in weathering tests for 30 years and is projected to last up to 40 years under normal conditions. Cut edges hold up very well, but cutting the material with an abrasive blade is discouraged as the filings will mar the surface. Galvalume® costs about 10% more than standard galvanized steel.
Aluminum Metal Roofing System Properties
Aluminum that is anodized or painted is highly resistant to corrosion, making it well-suited to coastal environments (although lightweight aluminum flashings tend to pit and oxidize in salty air). Its light weight is an advantage in reroofing. Because of its high coefficient of expansion, however, attachment systems must be designed to accommodate the movement of long panels. And since it has a lower tensile strength than steel, more fasteners may be required to achieve wind ratings comparable to a steel roof. Also, aluminum has a low melting point so it relies on two layers of fire-resistant underlayment, such as VersaShield, to get a Class A fire rating. Most aluminum used in roofing has a baked-on paint finish rather than an anodized finish. Although anodized aluminum is less costly, new paint technologies such as Kynar® and Hylar® carry better warranties and are available with a low-gloss finish generally favored on roofs. Some coated aluminum products come with transferable lifetime warranties.
This high-end material is highly resistant to corrosion and easily formed into panels. Copper roofs have been known to last for over a century and are a common sight on churches and historic buildings. Left unfinished, the material will oxidize to the familiar green patina that protects the underlying metal. In arid areas, the color may be more reddish-purple. Special clear acrylic coatings can be applied that will help copper retain its original color.
One concern is that runoff from a copper roof can stain building components below if not managed with gutters. Also, premature failure of copper flashing and roofing has been linked to acid rain and runoff from cedar shingles (see “Flashings” under “Wood Shakes and Shingles,” page 92 in the printed text Best Practices Guide to Residential Construction).
Clients interested in copper should consider a newly developed proprietary sheet metal called Suscop™, which has copper plating over a stainless-steel core. The material combines the strength and durability of steel with the natural patina of real copper . Because of its greater strength, a lighter-weight sheet (0.4mm) can be used in place of 16-ounce copper, significantly reducing material costs.
Zinc Metal Roofing System Properties
Zinc roofs are similar to copper in their durability but weather to a bluish-white color rather than green. The material is very malleable and can be formed into intricate patterns for metal shingles.
Details about the various metals used in roofing are at METALS USED IN ROOFING and at A Complete List of Types & Properties of Metal Used in Roof Systems.
Details about galvanic corrosion and other metal roof corrosion hazards are at GALVANIC SCALE & METAL CORROSION. Excerpts are below.
With metal roofing or any metal building components, the safest strategy is not to mix metals that come in direct contact with one another. Use aluminum flashing and fasteners with aluminum roofing, copper flashing and copper nails with copper roofing, etc. When this is not possible, choose a second metal that is not likely to lead to galvanic corrosion or use a physical barrier to separate the two metals.
What is the Galvanic Scale?
The galvanic scale (see Table 2-11) ranks a metal’s tendency to react in contact with another metal in the presence of an electrolyte, such as water or even moisture from the air. Metals at the top of the chart are called anodic, or active, and are prone to corrode; metals at the bottom are cathodic, or passive, and rarely corrode. The farther apart two metals are on the chart, the greater their tendency to react and cause corrosion in the more active metal. Metals close to each other on the scale are usually safe to use together.
The Area Effect Determines the Rate of Metal Corrosion
The rate of corrosion is controlled by the area of the more passive metal. For example, a galvanized steel nail (active) will corrode quickly if surrounded by a large area of copper flashing (passive). If a copper nail is used in galvanized steel flashing, however, the corrosion of the steel will be slow and spread over a large area, so it may not be noticeable. In each case, the active metal corrodes, and the passive metal is protected.
Galvanic Corrosion of Metal Roofing
Because they are made from active metals, aluminum and zinc roofing panels, as well as steel roofing with aluminum and zinc coatings (galvanized steel, Galvalume®, etc.), are vulnerable to galvanic corrosion if allowed to come in contact with more passive metals. For example, never use copper or lead flashings with aluminum, zinc, or galvanized roofing materials. Even water dripping from a copper pipe, flashing, or gutter can lead to corrosion of coated-steel or aluminum roofing materials. How common flashing materials react with metal roofing and other metal building materials is shown in Table 2-12.
Where incompatible metals must be used in close proximity, use the following precautions:
Other Incompatible Materials Found on Metal Roofs
In addition to galvanic corrosion, a number of other common building materials can harm the finishes on metal roofing or lead to etching or corrosion of the material itself:
Wet Mortar Effects on Metal Roofing
Aluminum roofing materials and aluminumbased coatings can be damaged by alkali solutions such as wet mortar. Where contact with wet mortar cannot be avoided, one option is to spray the metal with lacquer or a clear acrylic coating to protect it until the mortar is dry.
Pressure-Treated Wood Effects on Metal Roofing
Roof panels treated with aluminum and zinc coatings should not come into direct contact with pressure-treated (PT) wood, which can damage the finish and accelerate corrosion.
Sealants & Caulks Impact on Metal Roofs
Use only sealants recommended by the manufacturer. Never use acid-cure silicones (the most common type, with a vinegar smell) or asphalt roofing cement with coated-steel roofing, as these will mar the finish. Commonly recommended products include butyl tape and gunnable terpolymer butyl or urethane sealant.
Salt Spray Impact on Metal Roofs
Saltwater spray is very hard on metalliccoated– steel products and may lead to corrosion within 5 to 7 years. In these areas, the best choices are copper, stainless steel, or painted aluminum. Hylar/Kynar® finishes hold up best.
Details about galvanic corrosion and other metal roof corrosion hazards are at GALVANIC SCALE & METAL CORROSION.
Details about paints and coatings used on metal roofs are found at METAL ROOF COATINGS & PAINTS. Excerpts are below.
While unpainted metal roofs are common on utility buildings and some rustic homes, most homeowners prefer a painted surface. In addition to improving the appearance, a high-quality factory finish can significantly extend the life of metal roofing. In general, factory finishes are durable and flexible enough to tolerate factory roll-forming and bending on-site. The best finishes carry decades-long warranties against cracking and peeling, and “excessive” chalking and fading (as defined by the manufacturer). The quality of the finish is determined by the type of resin and the stability of the pigments.
Polyester-Resin Roof Paints for Metal Roofing
Polyester-resin paints are the least expensive and are commonly used on exposed-fastener panels. These have a medium to high gloss when applied, but they will fade significantly within 5 to 7 years on surfaces exposed to direct sun. Bright red, for example, may fade to pink. Fading will be less noticeable on light colors, making them a better choice. Warranties are typically for 3 to 5 years and rarely cover fading or chalking.
Silicone-Modified Polyester Roof Coatings
SMPs (siliconemodified polyesters) use polyester resins blended with silicone additives to improve performance. In general, the higher the silicone content, the more durable the finish. These are available in medium- and high-gloss colors, and they resist fading and chalking much better than standard polyester paints. Warranties against excessive fading and chalking typically run from 10 to 20 years, depending on the formulation.
PVDF Fluoropolymer Resin Roof Paints
Based on a fluorocarbon-based resin called PVDF, these are the most technically advanced and most expensive finishes. Sold under the trade names Kynar 500® and Hylar 5000®, fluorocarbon-based paints provide a smooth and dense medium-gloss finish that offers excellent durability and long-lasting resistance to fading and chalking, even under intense sun exposures. The Teflonlike coating also resists dirt retention and holds up better in coastal environments than other finishes. The finish is softer than SMPs, however, and can be damaged by the roofing installers, if they are not careful. Typical warranties run 20 years or greater, with 10- to 20-year protection against excessive fading.
Use of Reflective Finishes for Metal Roofs to Reduce Building Air Conditioning Costs
White metal roofs can reduce cooling loads by as much as 30%, according to tests conducted by the Florida Solar Energy Center. More modest savings are now available with dark colors as well by using metal shingles coated with special paints formulated to selectively reflect the sun’s infrared and ultraviolet radiation. These “Hi-R” paints are now standard options with Hylar/Kynar® finishes. Tests indicate that aluminum shakes with a reflective brown finish reject 30% to 40% of the total solar radiation compared to 67% for a white metal roof.
Granular Coatings Used on Metal Roof Shingles
Some metal shingles are available with a textured finish consisting of crushed stone or ceramic granules blended into an acrylic resin. These are applied over a special primer and sealed with a clear acrylic sealer. The multicolored granules give the appearance of an asphalt shingle and protect against scratching from foot traffic. The finishes also help protect against denting from hail and help conceal any small dents.
Details about paints and coatings used on metal roofs are found at METAL ROOF COATINGS & PAINTS.
Details about wood shingle and wood roof shake quality, types, warranties, & treatments are found at WOOD ROOF SHINGLE PROPERTIES. Excerpts are below.
Wood shakes and shingles are traditional American roof coverings dating back to Colonial times. They remain popular in many coastal areas and are common or even mandated in certain historic districts. Traditionally, wood roofs were laid on spaced sheathing, which provided good ventilation around the shingles and contributed to a service life of 30 years or more. New wood roofs set on solid sheathing have been known to fail in 10 years or less unless the installer takes adequate precautions to allow for good drainage and drying of the wood roofing materials. With installed costs of over $600 per square for premium materials, it is important to design a roof that will last.
Materials Used in Wood Shingle & Shake Roofs
Wood shakes and shingles soak up water through their end grain, dry unevenly in the sun, and slowly erode on the surface from a combination of ultraviolet radiation, wind, and precipitation. In humid conditions, wood shingles may become a breeding ground for moss, lichen, and decay fungi. To survive those harsh conditions, wood roofing should be made from a durable wood species that is either naturally decay-resistant or pressure-treated.
Wood Species for Wood Shingle or Shake Roofs
The most commonly used wood on roofs today is western red cedar. The heartwood of red cedar is rich in extractives that provide natural decay resistance. Eastern white cedar also has good decay resistance and is commonly used on the East Coast. However, white cedar is typically flat-sawn and has a mix of heartwood and sapwood, making it less durable on a roof and more prone to cupping and splitting. Other less common species with good track records are Northern white cedar, Alaskan yellow cedar (actually a cypress), and white oak.
Whatever species is selected, use the best grade available. With red cedar and other decay-resistant species, the heartwood is far more decay-resistant than the sapwood. Edge-grain wood is more stable and less prone to cupping and splitting than less expensive flat-grain wood. The best choice for wood roofing is all-heart, edge-grained shakes or shingles.
Wood Shingle & Shake Shingle Grade Choices
Make sure the lumber to be purchased has been graded under the authority of a recognized grading agency such as the Cedar Shake and Shingle Bureau for red cedar or the Southern Pine Inspection Bureau for yellow pine. A blue label on the packaging, for example, may simply be a marketing tactic and does not necessary indicate that the shakes or shingles are certified as Grade 1.
Wood Shingle & Shake Roof Warranties
If installed in accordance with the Cedar Shake and Shingle Bureau’s specifications by a certified installer, the CSSB will guarantee wood roofing for 20 to 25 years, depending on the thickness of the shake or shingle. Some pressure-treated shakes and shingles carry warranties of up to 50 years.
Preservative Treatment for Wood Shingle or Shake Roofs
If premium red or white cedar is too expensive, consider pressure-treated southern yellow pine shakes and shingles. In its favor, yellow pine is a tougher and stronger wood, and although not as pretty as red cedar when new, over time they will both weather to a similar silver gray. Because penetration of the treatment is nearly 100%, pressure-treated pine shingles carry guarantees against decay for up to 50 years, making them wellsuited to high-moisture environments, shallow slopes, and shady wooded sites where organic matter may collect on the roof. The preservatives should not leach out over time.
One drawback to yellow pine shingles and shakes is that many are flat-grained, so most come pretreated with a water repellent to help them resist cupping and splitting. However, retreatment with a water repellent at some point may be required for optimal performance. Western red cedar shingles are also available pressure-treated for severe applications where standard cedar shingles are prone to decay.
Characteristics & Grades of Wood Roof Shingles
Shingles are sawn from blocks of wood, which gives them two smooth faces. They are relatively thin and cut to a taper. Red cedar shingles come in four grades, but most roofs use No. 1 or No. 2, which are all edge-grain heartwood (Table 1-6, and at page 16 in the printed text Best Practices Guide to Residential Construction). They are available rebutted and rejointed (R&R), where a uniform appearance is desired, or machine-grooved for a textured surface.
Eastern white cedar shingles are also available in four grades. Most roofing work uses Grade A (Extra), which is all-clear, all-heartwood, or Grade B (Clear), which has no knots on the exposed face (see Table 1-7).
Characteristics & Grades of Wood Roof Shakes
Shakes are split from large blocks of wood and may be resawn to create a taper. They are heavier than shingles, less uniform in thickness, and are generally rough-textured on one or both sides creating a more rustic appearance. Grades and characteristics for red cedar shakes and shingles are found in Table 1-6. Red cedar shakes come either tapered or untapered and are usually installed on roofs in Premium or No. 1 grade.
Fire-Retardant Treatment for Wood Shingle Roofs
Once popular on the West Coast, wood roofs have been banned in many residential areas by fire regulations designed to slow the spread of wildfires.
Fire-retardant treated (FRT) shingles and shakes have been developed to address these issues and can obtain a Class B or C rating when combined with other components in a fire-resistant roof system. With pretreated shingles, consult with the treating company regarding fastener requirements and any special application instructions.
Details about wood shingle and wood roof shake quality, types, warranties, & treatments are found at WOOD ROOF SHINGLE PROPERTIES.
Recommended wood slopes and shingle exposures for wood shakes and shingles are detailed at WOOD ROOF INSTALLATION SPECS. Excerpts are below.
Details about felt underlayment requirements and wood shingle or shake course interlayment are provided at WOOD ROOF SHEATHING, UNDERLAYMENT. Excerpts are below.
Other than selecting a durable wood, the most important factor in determining a wood roof’s longevity is its ability to dry out from both top and bottom when wet. While this was a natural feature of traditional installations over spaced sheathing, new methods and products are required for installation over solid sheathing. The two main approaches are:
Specifications for Spaced Sheathing or "Skip Sheathing" for Wood Shingle & Shake Roofs
The traditional way to lay wood shakes and shingles on spaced sheathing was ideal for wood roof longevity, but it has largely fallen by the wayside. Spaced sheathing is especially beneficial in warm, high-moisture climates, since the gaps in the substrate allow the shakes or shingles to dry out from both sides. It is not recommended in areas of windblown snow and not always permitted structurally. Where allowed, spaced sheathing typically uses nominal 1x4s for shingles or 1x6s for shakes. Code requires a minimum 1x4, and the spaces between battens should not exceed 3 1/2 inches (Figurres 2-46 and 2-47).
The boards are spaced on centers equal to the weather exposure of the shakes or shingles, and they are lined up so the nailing falls in the center of each board. In areas where the average daily temperature in January is 25°F or less, solid sheathing is required on the lower section of the roof to support an eaves membrane. The eaves membrane should extend into the house 24 inches past the interior face of the outside wall.
Solid Sheathing Required for Wood Roofs in High Wind Areas
This is required in areas of high wind or seismic activity and wherever else a solid roof diaphragm is required by code. Solid sheathing is also recommended in areas subject to windblown snow. Because of their irregular surface, rustic-style shakes are partially self-ventilating and may perform adequately on solid sheathing in relatively dry climates. Pressure-treated shingles or shakes can also be installed over solid sheathing. Shingles or smooth-surface (taper-sawn) shakes, however, are more prone to moisture buildup over solid sheathing, so a batten system or a ventilating underlayment is recommended, as described below.
Battens Over Solid Sheathing Improve Wood Roof Venting
This provides the full benefit of spaced sheathing on top of a solid roof deck. After laying down No. 30 felt underlayment, install vertical 2x battens lined up with the rafters beneath for solid nailing. Next, place horizontal 1x4 or 1x6 battens (see “Spaced Sheathing,” above) and nail into the vertical battens (Figure 2-48).
At the upper and lower edges of the roof, use insect screening or matrix-style roof vent material to block the entry of insects and other pests. Shake and shingle installation proceeds as for spaced sheathing.
Underlayment Specifications for Wood Shingle & Shake Roofs
Wood Roof hingles: Over solid sheathing, use minimum No. 30 felt lapped at least 3 inches horizontally and 6 inches at end laps. Over spaced sheathing, no underlayment is used except at the eaves if eaves flashing is required.
Wood Roof Shakes: Over solid or spaced sheathing, use 18-inchwide “interlayment” strips of No. 30 felt installed between shakes, as described below (Shake Installation, below).
Ventilating Underlayments Used with Wood Shingle/Shake Roofs
Many installers are shifting to a ventilating underlayment such as Cedar Breather (Benjamin Obdyke), which is easy to install and only adds about 10% to the cost of a wood roof. Cedar Breather is three-dimensional nylon matrix with dimples on the bottom and a smooth top surface. It lays over the felt paper and is tacked in place. It creates a continuous air space below the roofing, helping the shingles to dry out more rapidly and evenly.
Although the air space is only about 1/4 inch, contractors report that it reduces cupping and splitting. And by speeding up drying time, the air space should also help reduce the growth of decay fungi. However, ventilating underlayments are too new to draw conclusions about long-term performance. Installation details are shown in Figure 2-49.
Eaves Flashing Details for Wood Shingle & Shake Roofs
Apply eaves flashing to either spaced or solid sheathing in regions with an average daily temperature of less than 25°F (under the IRC) or in other areas prone to ice and snow buildup. The eaves flashing should extend up the roof to a point 24 inches inside the building. Where eaves flashing is required with spaced sheathing, install solid sheathing along the bottom section of the roof to support the eaves flashing.
Details about felt underlayment requirements and wood shingle or shake course interlayment are provided at WOOD ROOF SHEATHING, UNDERLAYMENT.
Fastener Sepcifications for Wood Shingle & Shake Roofs: Nails, Staples
Details about nailing or stapling wood shingles or shakes are provided at WOOD ROOF INSTALLATION SPECS. Excerpts are below.
All nails should be either stainless steel (type 304 or 316), hot-dipped galvanized, or aluminum. Staples should be either stainless steel or aluminum. Galvanized staples will not last the life of the roof. Treated shingles may require stainless steel or other special fasteners. Consult with the treatment company for recommendations. Stainless steel is also the first choice in coastal environments.
Wood Shingle Installation Specifications
Details on how to install, lay out, space, expose, and nail wood shingles are provided at WOOD ROOF INSTALLATION SPECS. Excerpts are below.
Whether installed over solid sheathing or spaced sheathing, follow these guidelines:
Details about nailing or stapling wood shingles or shakes are provided at WOOD ROOF INSTALLATION SPECS.
Wood Shake Roof Installation Specifications
Details for installing wood shake roofs are at WOOD ROOF SHAKES INSTALLATION. Excepts are below.
Whether installed over spaced or solid sheathing, shakes should always be interlaid with 18-inch-wide strips of No. 30 roofing felt. The felt strips acts as baffles to keep windblown snow and other debris from penetrating the roof system during extreme weather. The felt “interlayment” also helps shed water to the surface of the roof. It is important to locate each felt strip above the butt of the shake it is placed on by a distance equal to twice the weather exposure (Figure 2-51).
Placed higher, the felt strips will be ineffective. Placed too low, they will be visible in the keyways and will wick up water, leading to premature failure of the shakes. In addition, follow these guidelines:
Details about when and how wood shingles or shakes may be used in re-roofing or roofover jobs are provided at WOOD SHINGLES, RE-ROOFING WITH. Excerpts are below.
Under some conditions, shakes and shingles can be installed over existing roofing, as follows:
Advice for Installing Wood Shingles or Shakes Over Existing Asphalt Shingles
If the existing asphalt shingles are not overly cupped or deteriorated, split or rough-sawn shakes can be installed over the shingles using interlaid strips of felt, as described above. Installing wood shingles over asphalt, however, requires a ventilating underlayment such as Cedar Breather or a system of battens (as shown in Figure 2-47 and Figure 2-48).
Advice for Installing Wood Shingles or Shakes Over Existing Wood Shingles
If the shingles are not badly curled or deteriorated, they can form an adequate surface for new shingles or shakes. Do not place building felt under the new shingles as that could inhibit drying, but if there is a high risk of decay (moist environment, low slope, overhanging trees), a layer of Cedar Breather is recommended. Shakes should be installed in the normal fashion with interlaid felt. Use nails long enough to penetrate the sheathing.
Advice for Installing Wood Shingles or Shakes Over Existing Shakes
In most cases, these will need to be removed before reroofing, as the surface is too irregular, and nailing through the shakes into solid sheathing is impractical.
Details about when and how wood shingles or shakes may be used in re-roofing or roofover jobs are provided at WOOD SHINGLES, RE-ROOFING WITH.
Details about wood shingle or shake roof hip and ridge installations are provided at Wood Roof Hip & Ridge Details. Excerpts are below.
The traditional treatment at hips and ridges is a laborintensive “woven” cap, consisting of alternating sets of two beveled shingles. Many installers now use factoryassembled cap pieces that speed up the process.
Wood Shingle/Shake Roof Hips
Lap the underlayment over the hip before installing the shingles. Then install a strip of roofing felt or metal flashing up the hip on top of the shingles before nailing the caps in place. Use nails or staples long enough to penetrate the sheathing by 3/4 inch.
Ridge Details for Wood Shingle / Shake Roofs
For a vented ridge, use a plastic, matrix-type ridge vent. Cover the ridge vent with a strip of roofing felt and install factory-assembled ridge cap pieces. To prevent splitting of ridge-cap shingles, it is best to install them with a pneumatic nailer or stapler.
Details about wood shingle or shake roof hip and ridge installations are provided at Wood Roof Hip & Ridge Details.
Details about flashing for wood shingle or shake roofs are provided at FLASHING WOOD ROOF DETAILS. Excerpts are below.
Roof flashings should be at least 26-gauge, corrosionresistant sheet metal, preferably painted galvanized steel or painted aluminum.
Copper Flashing and Cedar Roofing?
Copper is a popular flashing material with wood roofs, although some experts caution against using copper in direct contact with red cedar or its runoff, since the soluble tannins in cedar can etch copper and, in extreme cases, lead to perforation of the flashing within 10 to 20 years (see also “FLASHING WALL DETAILS - Copper,” and “Metal Choices for Metal Roof Systems - Copper”).
Premature wood shingle roof failures have been documented in areas of the eastern United States that are subject to acid rain, leading the Cedar Shake and Shingle Bureau to advise against using copper flashing in areas east of the Great Lakes that are exposed to acid rain.
Another approach endorsed by the Copper Development Association is to design flashing joints with a cant or hem that holds the edge of the cedar shingle slightly away from the flashing. The gap prevents water from being wicked into the joint, bathing the copper in the acidic solution.
Valley Specifications for Wood Shingle/Shake Roofs
Wood roofs typically use open valley designs. While the International Residential Code (IRC) only requires the valley flashing to extend a minimum of 10 inches up each side of the valley for shingles and 11 inches for shakes, most contractors install 24- to 36-inch-wide valley flashing based on the area and pitch of the roof planes being drained.
The valley metal should be protected by an extra layer of 36-inch-wide No. 30 felt installed directly under the metal or a layer of self-adhesive bituminous membrane applied directly to the sheathing. It is best to set aside the widest shingles or shakes for use in the valley to keep nails at least 12 inches from the valley centerline (Figure 2-52).
Chimneys and Skylight Flashing Specifications for Wood Shingle/Shake Roofs
These are flashed conventionally, using step flashing on the sides in accordance with Table 2-16. Use a soldered apron flashing below the chimney and a soldered head flashing at the top. Larger chimneys with significant water flow behind them should have a cricket above.
Details about flashing for wood shingle or shake roofs are provided at FLASHING WOOD ROOF DETAILS.
Detailed advice about cleaning and maintaining wood shingle or wood shake roofs are provided at WOOD ROOF MAINTENANCE. Excerpts are below.
A number of factors affect the longevity of a wood roof. Key factors include the durability of the wood, local humidity and precipitation levels, and whether the roofing was installed with adequate ventilation.
Other factors include the slope of the roof (steeper slopes shed water faster) and the presence of overhanging trees that shade the roof and drop organic debris onto the roof, trapping moisture on the surface. Some of these factors can be controlled by the contractor; some managed by the homeowner. Others, like the weather or the reduced durability of second-growth cedar, are beyond our control.
Some simple steps that a homeowner can take to prolong the life of a wood roof include:
Over time, the natural extractives in cedar and other decay-resistant species will leach out, making the wood vulnerable to decay. Also, as the shingles dry out, they are prone to cupping, checking, and splitting. At some point, it may make sense to wash and treat the entire roof.
Washing or Cleaning Advice for Wood Roofs
Cleaning wood roofs with high-pressure equipment is controversial and, in untrained hands, can cause significant damage. It is best to use normal garden hose pressure along with a brush or pump sprayer. To remove dirt, mildew, and weathered gray residue, a consortium of wood technology and coatings experts, including the U.S. Forest Products Laboratory (FPL), recommend a solution of sodium percarbonate (disodium peroxydicabonate) and water. With redwood and cedar, a second wash with a solution of oxalic acid may be needed to remove brown and black discoloration caused by tannins that leached out of the wood. Concentrated oxalic acid is toxic and should be handled with care.
Preservative Treatments for Wood Shingle / Shake Roofs
There are a number of commercial treatments available to restore decay-resistance to an aging wood roof. One effective and relatively benign (to plants) treatment consists of a copper-naphthenate compound called Cunapsol 5, which is diluted 1:4 with water and can be applied with a garden sprayer. The treatment needs to be repeated approximately every five years.
Oil-Borne Wood Roof Preservatives
Although Cunapsol 5 and similar waterborne treatments offer good protection against mold, mildew, and decay fungi, they will not do anything to slow down the cupping and splitting caused by weathering. For that, an oil-borne treatment is required. Effective treatments include copper naphthenate with a 3 to 4% metal content and copper octoate with a 1 to 2% metal content. These can be brushed on or dipped (before installation) or professionally applied with spray equipment.
Semitransparent Oil-Based Preservative Stains on Wood Roofs
Semitransparent oil-based preservative stains work well on rough-textured wood, such as shakes and shingles. They provide some pigmentation and protect the roof from decay for several years. Look for a product with both a wood preservative and a water repellent.
Stains with a high percentage of pigment provide the best protection against UV degradation. While preservative stains are best applied before installing the shingles, a surface application can significantly extend the life of a wood roof.
Treatments to Use and to Avoid on Wood Shingles and Shake Roofs
According to the Shingle and Shake Bureau, one should use only products that are marketed and labeled as a cedar roof treatment, that have an MSDS available, and that contain one or more of the following: a water repellent, UV inhibitor, or U.S. EPA-registered wood preservative. The following treatments should never be used on wood shingles or shakes:
Detailed advice about cleaning and maintaining wood shingle or wood shake roofs are provided at WOOD ROOF MAINTENANCE.
Details about low slope roofing are found at LOW SLOPE ROOFING. Excerpts are below.
Most roof coverings can be applied on roofs as shallow as 2:12 as long as a fully waterproof membrane is installed over the decking. In this case, the finish roofing material, whether asphalt shingles, wood, or tile, functions mainly as a decorative element but also helps protect the underlying membrane from UV radiation and physical damage.
At slopes lower than 2:12 on residential structures, the primary roofing options are built-up roofing (BUR), often called “tar and gravel,” modified bitumen, and EPDM (see Table 2-17). In addition, a handful of proprietary singleply membranes designed for easy application to small jobs have entered the market and offer a few new choices. While some of these products look promising, how long a new product will perform over 20-plus years is uncertain.
Minimum Slope for Low-Slope Roof Systems
With any roofing material, a slope of at least 1/4 inch per foot is recommended to promote drainage and minimize ponding. Where deflection from snow or other live loads is a concern, a greater slope will be needed to prevent any ponding. Most manufacturers of low-slope roofing products specify a minimum slope of between 1/4 and 1/2 inch per foot in their warranties.
While membranes, such as vinyl or EPDM, are unaffected by standing water, it will shorten the life of asphaltbased materials, such as BUR and modified bitumen. With any roofing material, ponding of water increases the likelihood of leakage, increases deflection in the roof framing, and contributes to rooftop growth of mosses, algae, and other plant life. Also, the freezing and thawing of ponded water can harm most roof surfaces.
See these articles on flat and low slope roofing materials and designs:
Details about roll roofing are found at ROLL ROOFING, ASPHALT. Excerpts are below.
The simplest product to install on a small section of lowslope roof is 90-pound roll roofing. This consists of a heavy, asphalt-saturated organic or fiberglass felt with a granular surface. Rolls are 36 inches wide and weigh 90 pounds. Single-coverage roll roofing typically has a 2-inch lap with exposed nails and is used mainly on utility structures.
Double-coverage roll roofing is installed with a full 19-inch lap joint, leaving a 17-inch exposure, with a 2-inch head-lap. Nails are concealed under the lap joints that are sealed with asphalt lap cement. With two layers of protection, double-coverage roll roofing is acceptable for small roof areas and can be used on roofs as shallow as 1:12.
Details about BUR are found at BUILT UP ROOFS. Excerpts are below.
Built-up roofing (BUR) systems dominated the commercial and residential low-slope roofing markets until the 1980s, when single-ply membranes became widely accepted. BUR roofs consist of layers of asphalt-impregnated felt bonded with hot asphalt, or in some parts of the country, hot coal tar. The average life span of a hotmopped BUR roof is 15 to 20 years, although this can be extended by applying an aluminum coating every three to five years to reduce UV degradation and alligatoring.
BUR roofs can have either a smooth coated surface or a stone surface created by spreading crushed stone or gravel into a thick flood coat of hot asphalt or tar. Aggregate-faced roofs are typically more durable due to the heavier flood coat and the protection offered by the stone from UV radiation, hail, and other environmental wear and tear. However, the stone coating makes leaks harder to find and repair.
Proper detailing of metal flashings at openings, parapet walls, and roof edges for BUR roofs is critical, and these areas need regular inspection and maintenance. The most likely place for leaks is flashings, particularly metal edge flashings due to their thermal movement. Asphaltic or rubber flashings may also become brittle and crack.
Pros and Cons of Built-Up Roofs
BUR roofs are reliable if properly installed, and their multiple layers provide some protection against small installation errors. However, the long set-up time makes BUR expensive for small residential jobs. Also the heavy equipment, odors, and potential spills associated with a hot-mop job are not welcome on many residential job sites.
Details about modified bitumen roofing systems are found at MODIFIED BITUMEN ROOFING. Excerpts are below.
Most modified-bitumen roofs are torch-applied, although there are also self-adhesive and cold-process systems. The waterproofing membrane, sometimes called “single-ply modified,” consists of asphalt bitumen reinforced with a polyester or fiberglass fabric and modified with polymers to give it greater strength, flexibility, resistance to UV degradation, and resistance to heat and cold.
A variety of different chemical formulations have been tried over the years. It is best to stick to a product with an established track record. In general, modified-bitumen roofs can be applied to slopes as shallow as 1/4 inch per foot.
Installation Methods for Modified Bitumen Roofs
A torch-applied, or torchdown, roof starts with a nonflammable base sheet made of asphalt-saturated felt or fiberglass that is mechanically attached to the roofing deck. In residential construction, the base sheet is usually attached with roofing nails driven through metal caps.
The second layer is the waterproofing membrane, or cap sheet. This is heated with a torch as it unrolls, fusing it to the base sheet, to itself at seams, and to penetrations such as skylights. Installers must learn to heat the membrane so it is hot enough to fuse but not so hot as to burn through.
Membranes may be either smooth or have a granular surface like roll roofing. Smooth-faced membranes need a third coating, which has colored or reflective pigments to protect against UV radiation. The smooth type is preferable where foot traffic is expected or where decking is going over the roofing.
Torchdown roofing is self-flashing and uses no adhesives or solvents to seal around openings. The material can be run up parapets and abutting wall, and patches are used to seal around metal skylight curbs and similar openings. A special patching compound is used to seal to PVC stacks. If applied correctly, the torchdown membrane is essentially seamless.
Pros and Cons of Modified Bitumen Roofs
Modified bitumen is easily repaired without solvents or adhesives. It is compatible with asphalt shingles and asphalt compounds, although patching with roofing cement is not recommended. The reinforced fabric layer isolates the membrane above from building movement and gives the material enough strength to support occasional foot traffic.
The main drawback of modified bitumen roofing is the risk of fire during installation. While the risk of fire is low in the hands of trained installers, care must be taken when using torchdown on a wood-frame structure. A number of fires have started with sawdust that has accumulated in empty cavities, such as crickets and parapets. Inspection of the roof for sawdust pockets while it is being framed is advised.
Details about EPDM rubber membraner roofs are found at EPDM ROOFS. Excerpts are below.
While a variety of single-ply roofing membranes are used on commercial jobs, only EPDM has become widely used on residential sites. EPDM, a form of synthetic rubber, owes its popularity to its relative ease of installation combined with exceptional durability. If installed correctly, roofs often exceed 20 years of service and callbacks are exceedingly rare.
While some commercial EPDM systems are loose-laid or ballasted, residential applications are typically fully adhered. Rolls typically vary from 10 to 50 feet in width and from 50 to 200 feet in length, but many distributors will cut a piece to size for smaller jobs. If possible, use a single piece with no seams for the field of the roof. EPDM membranes are available in two thicknesses: .045 inch and .060 inch.
For fully adhered applications or any application where foot traffic or decking is planned, the thicker membrane is recommended.
Substrates for EPDM Roofs
EPDM can be bonded to a wide variety of substrates, including plywood, OSB, fiberboard, and urethane insulation board. The substrate should be smooth, even, and free of debris. Fasteners should be driven flush except in the case of insulation fastening caps, which project their shape though the membrane. If the surface is uneven or deteriorated, a layer of fiberboard or thin plywood should be installed first.
Installation Details for EPDM Roofs
After cutting the material to fit, installers use a roller to apply a proprietary contact cement to both the membrane and the substrate. Typically, a length of roofing is set in place and folded in half lengthwise so onehalf can be glued at a time. The adhesive should be fully dry on both surfaces before bonding, or bubbles may develop. Also, care must be taken to smooth out wrinkles and air pockets as the two surfaces are mated. Where seams are required, the material is lapped 4 to 6 inches and sealed with either double-faced seam tape or a special adhesive used for bonding rubber to rubber.
At openings, inside corners, outside corners, and other irregular shapes where the EPDM roof membrane has been cut, patches of uncured EPDM are applied using the rubber-to-rubber adhesive. The uncured form of EPDM is highly elastic and can be stretched to conform to irregular shapes.
The material is lapped up abutting walls and serves as its own flashing. Other terminations are usually sealed with an aluminum termination bar or an aluminum flashing covered with a strip of EPDM. Finally all exposed edges of EPDM at laps, patches, and terminations are sealed with a bead of proprietary caulking that protects the edge and acts as an extra water stop. Self-Adhesive.
For small EPDM roof jobs, a few manufacturers offer a peel-and-stick version of EPDM. Installation is similar to standard EPDM but may require a primer on plywood and OSB substrates. Seams generally require a proprietary adhesive with special caulking on exposed edges. Although the square foot cost is greater than with siteglued EPDM, on small jobs labor savings offset the higher material costs.
Pros and Cons of EPDM Roofing
While not intended as a walkway, EPDM works well as a substrate under rooftop decks. Leftover strips of membrane should be used to cushion the roofing from wood sleepers. Leaks are rare and usually can be traced to sloppy sealing of joints. Leaks are also relatively easy to identify and fix. One caution is that EPDM can be damaged by grease and petroleum-based products, a potential problem with outdoor grills and spillage of oil-base finishes used on siding or wood decking.
Details about walk-on roof surfaces are found at WALK-ON ROOF SURFACES, excerpts are below.
For rooftops that will also serve as decks (see “Rooftop Decks,” page 150 in the printed text Best Practices Guide to Residential Construction), one option is to use a roofing material designed for foot traffic. Duradek (Duradek U.S. Inc.) is a sheet vinyl membrane similar to Hypalon but with a nonskid wear surface. It was developed over 25 years ago for waterproofing decks, balconies, and outdoor living spaces. For use over a living space, the manufacturer recommends its 60-mil Ultra series, which is warranted against leakage for 10 years.
Duradek is made of reinforced PVC sheet with heat stabilizers and additives for resistance to fire, UV degradation, and mildew. The wear surface is textured for slip resistance and available in a variety of colors.
Installation Tips for Walk-On Roofs
Installation is similar to other single plies and must be done by factory-certified contractors. The membrane glues to almost any clean substrate with either a proprietary contact cement or a special water-based adhesive applied with a notched trowel. Seams are heat welded with a heat gun, the most critical step. Like other single-ply membranes, the material is self-flashing at abutting walls and penetrations.
Pros and Cons of Duradek Walkable Roofing Membranes
Duradek creates an attractive and durable no-skid deck surface that can withstand normal wear and tear, direct sun exposure, high winds, and freeze-thaw cycles. However, because the membrane is also the wear surface, it can be damaged by cigarette burns, punctures, and heavy abrasion.
Extensive details about roof ventilation are found at ROOF VENTILATION SPECIFICATIONS. Excerpts are below.
All residential building codes require some form of roof ventilation. These rules were first developed in the 1940s, when attic spaces first started to develop problems with mold and mildew due to excess moisture. With the growing use of plywood, asphalt shingles, insulation, and better doors and windows, houses were being built tighter. The tighter spaces retained more of the normal household moisture generated by cooking, bathing, household plants, crawlspaces, and exposed basement slabs. As the stack effect drove this moisture up into attic spaces, problems ensued.
Building Code Requirements for Roof Ventilation
The rules of ventilation developed by researchers in the 1940s were adopted first by the Federal Housing Administration (FHA) and later by all the major residential building codes, including the 2003 IRC, with few changes. Most asphalt shingle manufacturers will void their warranties if these rules are not followed. They require:
Details about cathedral ceiling ventilation and ceiling leak points are at CATHEDRAL CEILING VENTILATION. Excerpts are below.
Although the code-mandated ventilation rate has proven adequate under normal conditions, homes with highmoisture levels and air leaks in ceilings may still experience problems such as moldy sheathing. Cathedral ceilings are at the greatest risk due to the limited ventilation path.
The best defense against problems is to create a continuous air and vapor barrier between the living space and attic or roof cavity by carefully sealing all air leaks. The ceiling air barrier may consist of foam insulation with taped seams, taped polyethylene sheeting, or finished drywall that is sealed at corners and top plates with gaskets or sealants.
Penetrations & Roof Ventilation Challenges
Pay special attention to penetrations in the ceiling plane, particularly in cathedral ceilings. Chimneys, recessed lights, plumbing chases, and holes drilled through top plates for plumbing or wiring should all be sealed (Figure 2-53).
Plug holes with durable materials, such as expandable urethane foam, foam backer rod, EPDM, or sheet metal, and use long-lasting sealants such as high-quality urethanes, silicones, and butyls.
With a tightly sealed ceiling, attic moisture is no longer a significant problem. Attic ventilation is still recommended for three other reasons:
Extensive details about the cause and prevention of ice dams on roofs are at ICE DAM PREVENTION. Excerpts are below.
Ice dams form when heat leaking into attics or roof cavities from the building below, or from attic ductwork, melts the bottom layer of snow on the roof. The melt water runs down the length of the roof to the eaves, where it refreezes, forming a dam and icicles. In the worst cases, liquid water pools behind the dam and flows under the shingles and into the building (Figure 2-54).
Research has indicated that the ice-dam risk is greatest when temperatures range between 15°F and 20°F— when it is warm enough for snow to melt but cold enough for it to refreeze at the eaves. Also, the greater the depth of snow on the roof, the greater the risk of ice dams due to the insulating value of the snow itself.
Cold Roofs Prevent Ice Dams
Ventilation helps prevent ice dams by keeping the roof surface cold enough to limit uneven melting. Tests conducted in 1996 at the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL), showed that the traditional 1:150 ventilation rule was sufficient to prevent ice dams on roofs with R-25 or greater ceiling insulation. The 1:300 rule proved adequate for roofs with R-38 or greater insulation. Since most standard eave and ridge vents sold today meet the higher ventilation rates, most new homes are protected as long as there are no large heat leaks into the attic, or tricky sections of the roof with inadequate ventilation.
Details about reducing building cooling costs and cooling loads by the combination of factors listed below are found at COOLING LOAD REDUCTION by ROOF VENTS. Excerpts are below.
Experts recommend using attic ventilation in hot climates as part of an overall strategy to reduce cooling loads. Ventilation helps even more when used in combination with radiant barriers.
Benefits of Roof Ventilation Alone
Researchers at the Florida Solar Energy Center (FSEC) have found that adequate attic ventilation can modestly lower sheathing and shingle temperatures, and reduce an average home’s cooling load by about 5%.
Roor Ventilation and Radiant Barriers
Details about the benefits and effects of radiant barriers on heating costs, cooling costs, and roof shingle life are found at RADIANT BARRIERS. An excerpt is below.
For greater savings on cooling, consider adding a radiant barrier to the underside of the roof sheathing or draped between the rafters. This can reduce peak cooling loads by 14 to 15% and seasonal loads by an average of 9%. By doubling the roof ventilation from 1/300 to 1/150, the annual savings from radiant barriers rises to 12%. These numbers assume R-19 ceiling insulation and cooling ducts located in the attic, which are typical in Florida. With R-30 ceiling insulation, the cooling benefits of radiant barriers are less dramatic.
Roofing Color Effect on Cooling Costs
Details about the effects of roof color on cooling costs and roof life are at ROOF COLOR RECOMMENDATIONS. Excerpts are below.
Tests at FSEC also indicate that simply switching from dark to white asphalt shingles in a cooling climate can reduce peak cooling loads by 17% and seasonal loads by 4%.
The greatest savings resulted from using white metal roofing (see Table 2-18.)
Unvented “Hot” Roof Designs Where Venting is Difficult
Details about hot roof designs are found at HOT ROOF DESIGNS: Un-Vented Roof Solutions. Excerpts are below.
In cathedral ceiling configurations where it is difficult to provide ventilation, some builders have eliminated the vent space, relying instead on careful sealing of the ceiling plane to prevent moisture problems. While experts concede that this should work in theory, most caution that it is difficult to build a truly airtight ceiling assembly. Also, cathedral ceilings are slow to dry out if moisture problems do occur, whether from condensation or roofing leaks. If a hot roof is the only option for a section of roof, take the following precautions:
Details about proper roof space ventilation and attic ventilation are at ROOF VENTILATION SPECIFICATIONS.
Soffit and Ridge Vents
For both attics and cathedral ceilings, roof ventilation works best when it is balanced between high and low to take advantage of natural convection (Figure 2-55).
This configuration also tends to evenly wash the underside of the roof with ventilation air. The soffit-vent area should be equal to or slightly larger than the ridge-vent area. Ridge vents should either have external or internal baffles to minimize infiltration of windblown rain and snow. Use insulation baffles or modified framing to make sure that the ceiling insulation does not block airflow at the eaves (Figure 2-56.)
Ridge Vent Alternatives
Where ridge vents are not an option, combine any type of upper vent such as gable-end vents, roof vents, or turbines, with soffit vents. Where soffit vents are not possible, use gable-end vents on both ends of the roof, which will ventilate adequately under wind pressure. Avoid High Vents Alone. Do not use ridge vents or other rooftop vents without low vents to provide makeup air. The suction created could help pull moist household air into the attic.
Cathedral Ceiling Ventilation Details
Cathedral ceilings require the same continuous air barriers, and balanced soffit and ridge vents, as attics. Both air sealing and ventilation are more critical, however, since any trapped moisture in the roof cavity will remain longer and potentially cause greater damage than in an open attic. Also, since there is little or no communication from bay to bay, an effective ventilation system must reach every bay (Figure 2-57).
Hips and Valleys: Roof Ventilation Details
Ventilating hips and valleys can be challenging with a cathedral ceiling. One approach is to use a double or triple hip or valley rafter one size smaller than the common or jack rafters. This will create a vent space along the top of the hip or valley rafter that can be used to supply ventilation air to the jack rafters (Figure 2-58).
Roof Ventilation at Skylights
Localized hot spots such as skylights can also lead to ice dams below, due to blocked ventilation as well as melt water from skylight heat loss. Notching the rafters on either side of the skylight will help maintain airflow above the skylight (Figure 2-59).
If icing is still a problem, add an interior storm window to reduce heat loss through the glass in cold weather. As a backup, it is always a good idea to seal the skylight curb and surrounding roof area with a bituminous membrane (see Figure 2-5).
-- Adapted with permission from Best Practices Guide to Residential Construction.
Atlas Roofing Corp. www.atlasroofing.com Fiberglass and organic felt shingles
Certainteed Roofing www.certainteed.com Fiberglass shingles
Elk Premium Building Products www.elkcorp.com Fiberglass shingles
GAF Materials Corp. www.gaf.com Fiberglass shingles
Georgia-Pacific Corp. www.gp.com/build Fiberglass and organic felt shingles
IKO www.iko.com Fiberglass and organic felt shingles
Owens Corning www.owenscorning.com Fiberglass shingles
Tamko Roofing Products www.tamko.com Fiberglass and organic felt shingles
Concrete Roof Tiles
Bartile Roofs www.bartile.com
Eagle Roofing Products www.eagleroofing.com
Entegra Roof Tile www.entegra.com MonierLifetile www.monierlifetile.com
Vande Hey-Raleigh www.vhr-roof-tile.com
Clay Roof Tiles
Altusa, Clay Forever LLC www.altusa.com
Ludowici Roof Tile www.ludowici.com
MCA Clay Tile www.mca-tile.com
U.S. Tile Co. www.ustile.com
Tile Fasteners and Adhesives
Dow Building Products www.dow.com/buildingproducts Tile Bond polyurethane foam tile adhesive
Fomo Products www.fomo.com Handi-Stick polyurethane foam tile adhesive
Newport Fastener www.newportfastener.com Twisted wire systems, hurricane clips, nose clips, and the Tyle-Tye TileNail
OSI Sealants www.osisealants.com RT 600 synthetic rubber tile adhesive
Polyfoam Products www.polyfoam.cc Polyset and Polyset One polyurethane foam tile adhesives
Wire works, Inc. www.wireworks-inc.com Tile hooks, hook nails, copper and stainless-steel nails
Low-Slope Roofing Membranes
Duradek www.duradek.com Vinyl roofing and walkable deck membrane
Firestone www.firestonebpe.com RubberGard EPDM residential roofing system
GenFlex Roofing Systems www.genflex.com Peel-and-stick TPO membrane
Hyload, Inc. www.hyload.com Kwik-Ply self-adhering polyester and coal-tar roofing membrane
Air Vent/A Gibraltar Company www.airvent.com A complete line of roof ventilation products, including shingle-over and exposed-ridge vents with exterior wind baffles and internal weather filters. Also soffit and drip edge vents and passive and powered attic turbine-type vents.
Benjamin Obdyke www.benjaminobdyke.com Shingle-over ridge vents. Low-profile Roll Vent uses nylonmatrix. Extractor vent is molded polypropylene with internal and external baffles.
Cor-A-Vent www.cor-a-vent.com Shingle-over low-profile ridge vents, including Cor-a-vent, Fold-a-vent, and X-5 ridge vent, designed for extreme weather. Corrugated core.
GAF Materials Corp. www.gaf.com Cobra vent: roll-out shingle-over ridge vent with a polyester-matrix core 102 CHAPTER 2 | Roofing
Mid-America Building Products www.midamericabuilding.com Ridge Master and Hip Master shingle-over molded plastic ridge vents with internal baffles and foam filter
Owens Corning www.owenscorning.com VentSure corrugated polypropylene ridge vents; also passive roof vents and soffit vents
Trimline Building Products www.trimline-products.com Shingle-over low-profile ridge vents, Flow-Thru battens for tile roofs
Elk Premium Building Products www.elkcorp.com Highpoint polypropylene shingle-over ridge vents
Tamko Roofing Products www.tamko.com Shingle-over ridge matrix–type Roll Vent and Rapid Ridge (nail gun version) and Coolridge, which is molded polypropylene with external and internal baffles
Benjamin Obdyke www.benjaminobdyke.com Cedar Breather, a 3/8 -in.-thick matrix-type underlayment designed to provide ventilation and drainage space under wood roofing
More Information about Roofing Materials, Methods, Standards
Asphalt Roofing Manufacturers Association (ARMA) www.asphaltroofing.org
Cedar Shake and Shingle Bureau www.cedarbureau.org
Metal Roofing Alliance www.metalroofing.com
Tile Roofing Institute www.tileroofing.org
-- Adapted with permission from Best Practices Guide to Residential Construction.
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