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ROOFING INSPECTION & REPAIR
AMERICAN CEMWOOD ROOFING
BEST ROOFING PRACTICES
BUILT UP ROOFS
CATHEDRAL CEILING VENTILATION
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY FLASHING Mistakes & Leaks
COLD WEATHER ROOF TROUBLE
DECKS, ROOFTOP CONSTRUCTION
EPDM, RUBBER, PVC ROOFING
EXTRACTIVE BLEEDING on SHINGLES
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
Green House or Solarium Roof Leaks
HEAT TAPES & CABLES on Roofs for Ice Dams
ROOF ICE DAM LEAKS
MASONITE WOODRUF FIBERBOARD ROOFING
NOISE CONTROL for ROOFS
PLASTIC ROOFING TYPES
PVC, EPDM, RUBBER ROOFING
ROOF ARCHITECTURAL STYLES - PHOTO GUIDE
ROOF CLEANING RECOMMENDATIONS
ROOF COLOR RECOMMENDATIONS
ROOF DORMER TYPES - PHOTO GUIDE
ROOF INSPECTION SAFETY & LIMITS
ROOF JOB PROBLEMS, RESOLVING
ROOF LEAK DIAGNOSIS & REPAIR
ROOF NOISE TRANSMISSION
ROOF REPLACEMENT SNAFUs
ROOFING FELT UNDERLAYMENT REQUIREMENTS
ROOFING MATERIALS, Age, Types
ROOFING TILE SHAPES & PROFILES
ROOFING UNDERLAYMENT BEST PRACTICES
SADDLE CONSTRUCTION at CHIMNEYS
SNOW GUARDS & SNOW BRAKES
STANDARDS for ROOFING
STRESS SKIN INSULATED PANELS
TEST LABS - ROOF SHINGLE
TREES & SHRUBS, TRIM OFF BUILDING
TRUSSES, Floor & Roof
UNDERLAYMENT REQUIREMENTS on ROOFS
VENTILATION in BUILDINGS
WALK-ON ROOF SURFACES
WARRANTIES for ROOF SHINGLES
WORKMANSHIP & ROOF DAMAGE
This article discusses best roofing practices for the installation of asphalt roof shingles, including installation temperature, shingle sealing methods, shingle course offsets, asphalt shingle nailing location and specifications, low slope and steep slope limits for asphalt shingles, and roof flashing at building eaves and around skylights. This article series discusses best practices in the selection and installation of residential roofing.
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Also see the roofing article links listed at Related Topics and our roofing home page: ROOFING INSPECTION & REPAIR.Adapted/paraphrased with permission from Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES:
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.
Details about the sealing recommendations from asphalt shingle roofing experts are at WIND DAMAGE to ROOFS and at CELLOPHANE STRIP REMOVAL? we include an exhaustive review of the argument around whether or not one should remove the cellophane strips from the back of asphalt roof shingles before they are installed [basically, no provided they are secure and in place].
Here is what the GAF Materials Corporation, Grand Timberline™ Premium Architectural Shingle Application Instructions say about the glue strips and cellophane. You'll note that we are to leave the cellophane in place, but if site conditions (high wind) require immediate shingle sealing, an extra step, using additional shingle tab adhesive, is permitted.
In cold climates, the asphalt shingle 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.
Our page top photo shows the standard sealant strips found on asphalt shingles, in this case a GAF® product we photographed at a Home Depot® store.
Details about the sealing recommendations from asphalt shingle roofing experts are at WIND DAMAGE to ROOFS.
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.
Shingle Laddering Not Recommended
As we discuss in detail at LADDERING vs STAIR STEPPING SHINGLES, 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.
Ladder style application of asphalt roof shingles 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.
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 above).
Overdriven nails or staples can cut into the shingle or crack it in cold weather.
Fastener Location Requirements for Asphalt Shingle Roofs - Where Do the Shingle Nails or Shingle Staples Go?
Shingle nail placement should follow manufacturers specs, which typically require nailing or stapling just below the sealant strip (Figure 2-11 at left).
Nailing the roof shingle too high can allow wind to get under the shingles.
Nailing the roof shingle too low will expose nails to the weather and to view from below.
Nailing the shingle through the sealant strip can interfere with sealing.
Shingle Nailing in Areas of High winds
Also special wind-rated shingles with heavier sealing strips are available by special order and may be required in some jurisdictions.
Nailing Requirements for Laminated or Architectural Asphalt Roof Shingles
Use 4 or 6 roofing nails in architectural shingles, as shown here.
With laminated asphalt roof shingles, standard nailing is four fasteners spaced equidistant as shown in Figure 2-12, or six fasteners equidistant for heavy-duty installations.
It is important that fasteners go in the designated nail area where they will penetrate both laminations.
Nailing a laminated or architectural asphalt roof shingle too high will leave the bottom lamination loose and subject to slipping out of place.
Low Slope Roof Specifications for Asphalt Shingle Roofs: Special Procedures
Asphalt shingles can be installed on roof slopes of 2:12 to 4:12 if special procedures are followed for underlayment (see details at OOFING UNDERLAYMENT BEST PRACTICES or see comments on page 54 in the printed text Best Practices Guide).
Eaves flashing to a point at least 24 inches inside the interior wall is recommended if there is any possibility of ice dams or water backup from leaves or pine needles.
A conservative approach is to run self-adhering bituminous membrane over the entire low slope area. Once the underlayment is complete, shingles are installed in the standard fashion. In cold weather, manual sealing may be required as wind uplift will be greater on shallow roofs (see manual sealing discussed at “WIND DAMAGE to ROOFS,” or see page 57 in the printed text Best Practices Guide).
Steep Slope Limits & Shingle Nailing and Hand Sealing Requirements for Asphalt Shingle Roofs
Asphalt shingles should not be installed on vertical walls, but they can be used on steep slopes, such as mansard-style roofs.
For slopes greater than 21:12, apply underlayment in the normal fashion.
However, shingle sealing may be a problem, particularly on shaded portions of the roof.
best performance, use the six-fasteners-per-shingle method
(Figure 2-11 at left) and manually seal the shingles with plastic
roofing cement (see manual sealing discussed at “WIND DAMAGE to ROOFS” ).
Nailing & Sealing Asphalt Shingles on Near-Vertical Building Surfaces
Our steep roof photo (left) shows quite a few shingles lost from this rather steep church roof slope. Similar problems occur when asphalt shingles are nailed to the steep sides of mansard roofs unless proper nailing and sealing have been performed.
Flickinger cites the NRCA Roofing and Waterproofing Manual 4th Ed where, in referring to roof slopes of 18" rise in 12" of run (150%) or more, [note that this is more cautious than Bliss's advice above] the NRCA (Flickinger) points out that there are differing views within the roofing industry about the maximum slope on which asphalt shingles may be applied using typical methods.
We discuss the recommended installation details for installing asphalt roof shingles on very steep or near vertical roof slopes and also use of roof shingles or even roll roofing on vertical building walls separately at ASPHALT SHINGLES on VERY STEEP ROOFS
Flashing Requirements for Asphalt Shingle Roofs
Flashings for asphalt shingles should be corrosion resistant metal with a minimum thickness of 0.019 inch. A cricket or saddle should be installed on any chimney greater than 30 inches wide and can be covered with flashing or the same materials used as a roof covering.
See these roof flashing articles:
FLASHING, ASPHALT SHINGLE VALLEYS
Underlayment Requirements for Asphalt Roof Shingles
The roof deck should be sound and level before laying the underlayment. Fifteen-pound or heavier felt underlayment is required by code in some areas. Whether or not it is required, underlayment is cheap insurance against problems. There are several good reasons to install underlayment:
Details about the requirements and benefits of roofing underlayments are at these articles:
Underlayment On Standard Slopes where Asphalt Roof Shingles are Installed
On roofs with a slope of 4:12 or greater, use a single layer of 15 lb. asphalt-saturated felt, starting at the eaves and lapping upper courses over lower by a minimum of 2 inches. Vertical joints should lap a minimum of 4 inches and be offset by at least 6 feet in successive rows (see Figure 2-2 at left).
Secure each shingle course along seams and edges with enough corrosion-resistant nails to hold it in place until the roofing is installed.
In high-wind areas, apply fasteners a maximum of 36 inches on-center along overlaps.
For best protection against leaks, run felt 6 inches over ridges and hips, from each direction, and 6 inches up any adjoining walls. Valleys should be lined with a full width of roofing felt (or bituminous membrane) pushed tight into the valley so there is no slack.
Side courses of underlayment should run over the valley lining and extend 6 inches past its edge. (see ASPHALT SHINGLE VALLEY FLASHING)
Underlayment Application of Asphalt Shingles on Low Slope Roofs
Start with a 19-inch strip of 15 lb. asphalt-saturated felt along the eaves, and lap succeeding courses by 19 inches as shown in Figure 2-3 at left.
Wherever there is a possibility of ice or snow buildup or the backup of water from leaves or pine needles, install a self-adhering bituminous membrane along the eaves that extends up the roof to a point at least 36 inches inside the interior wall line.
An alternative approach, not widely used
anymore, is to seal all laps in the lower courses of roofing
felt with lap cement or asphalt plastic cement.
In areas with extensive snowfall or windblown rain, the best protection against leakage is to cover the entire low-slope roof area with a bituminous membrane, as shown in Figure 2-4.
Vertical end laps should be at least 3 inches and horizontal laps 6 inches.
If the roof changes to a steeper slope, for example, where a shed dormer joins the main roof, extend the membrane 12 to 18 inches up the main roof slope.
Bituminous membranes are self-healing around nail holes, and because they bond fully to the sheathing, any leaks that occur cannot spread.
As a safeguard against expensive callbacks, many roofers now apply membrane to the entire surface of any roof with a slope of 4:12 or less.
Eaves Flashing Recommendations for Asphalt Shingle Roofs
The best defense against ice dams in cold climates is a so-called “cold roof,” consisting of high levels of ceiling insulation separated from the roof surface by a free-flowing vent space (see Preventing Ice Dams on Roofs).
Where a cold roof cannot be achieved due to complex roof shapes, unvented roofs, or retrofit constraints, ice dams may form during severe winters, in some cases, causing pooled water to wet wall cavities and interior finishes.
Where adequate insulation and ventilation cannot be assured, self-adhering bituminous eaves flashing should be installed.
The membrane should go from the lower edge of the roof to a point at least 24 inches inside the interior wall line (Figure 2-5 at left).
Where two lengths of eaves flashing meet at a valley, run each across the valley, starting with the length from the roof with the lower slope or lesser height. The valley flashing should later lap over the eaves flashing.
Skylights and Ice Dams on Asphalt Shingle Roofs
With deep snow, melting water from above and around the skylight can lead to ice dams below.
For full protection, some contractors extend the eaves membrane up to the bottom of any skylights and continue it around the sides and top of the skylight.
By wrapping the skylight curb with membrane as well, any potential flashing leaks are also eliminated as shown in Figure 2-5 at left.
See also “Skylight Flashing,” page 127 in the printed text Best Practices Guide
Drip Edge. Drip edge should always be used along the eaves to kick water away from the fascia, and it is a good idea along rakes as well.
Drip edge should lap over the underlayment at the rakes and under it at the eaves (as shown in Figure 2-6 at left).
Overlap joints in the drip edge by 2 inches. Shingles can be set even the with the drip edge or overlap by up to 3/4 inch.
Some manufacturers of eaves membranes specify that the drip edge be installed on top of the membrane along the eaves, violating the principle that upper layers of flashing should overlap lower layers.
To remedy the problem, the manufacturers suggest using a second strip of membrane to seal the top of the drip edge to the eaves membrane. In practice, however, most installers place the drip edge first and lap the eaves membrane over it, consistent with good building practice.
-- Adapted with permission from Best Practices Guide to Residential Construction.
Low-Slope Roofing Membranes
More Information about Roofing Materials, Methods, Standards
-- Adapted with permission from Best Practices Guide to Residential Construction.
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