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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
FLAT ROOF MOISTURE & CONDENSATION
GREEENHOUSE / SOLARIUM ROOF LEAKS
HEAT TAPES & CABLES for ROOF 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 INSPECTION SAFETY & LIMITS
ROOF LEAK DIAGNOSIS & REPAIR
ROOF NOISE TRANSMISSION
ROOF REPLACEMENT SNAFUs
ROOFING FELT UNDERLAYMENT REQUIREMENTS
ROOFING MATERIALS, Age, Types
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 the different types of metal used in metal roof systems, the properties of each metal, and their application, including galvanized steel roofs, aluminized steel roofs, galvalume roofing, aluminum roofs, copper roofs, and zinc metal roof systems. This article series discusses best practices in the selection and installation of residential roofing.
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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 below [Click to enlarge any image] lists the advantages, drawbacks, compatibility, and life expectancy of galvanized steel roofing, aluminized steel roofing, galvalume, aluminum, copper, and zinc metal roofing products.
[Click to enlarge any image]
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® Metal Roofing
Details about aluminum roofing materials are at ALUMINUM ROOFING, excerpts are below.
Aluminum that is anodized or painted is highly resistant to corrosion, making it well-suited to coastal environments provided it is factory-coated with a suitable finish. (although lightweight aluminum flashings tend to pit and oxidize in salty air).
Aluminum roofing's light weight is an advantage in reroofing. Aluminum roofing also reflects heat and may thus reduce building cooling costs in hot sunny climates.
Because of its high coefficient of expansion, however, attachment systems must be designed to accommodate the movement of long aluminum roof panels.
Also see ROOF NOISE TRANSMISSION where we describe the noise transmission properties of metal roofing.
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 (photo) 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
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.
Details about copper roofing are found
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.Details about galvanized metal roofing are at GALVANIZED STEEL ROOFS.
Also see COMPLETE LIST OF TYPES & PROPERTIES of METALS USED in ROOF SYSTEMS for more about galvanized steel roofing.
Also sold under the trade names Zincalume ® and Galval®, Galvalume® was developed in the early 1970s. The underlying steel is coated with a zinc aluminum alloy that combines the long-lasting protection of aluminum with the self-healing properties of zinc.
Details about Galvalume® are at GALVALUME METAL ROOFING
Also see A Complete List of Types & Properties of Metal Used in Roof Systems for more about Galvalume.
Stainless steel is generally a rust-resistant material but it's corrosion resistance to salt depends on the stainless steel alloy or grade. Also, stainless steel roofing durability depends on installation and ventilation details. Stainless steel grade 316) work well is suitable for salt-spray areas.
Terne coated stainless steel roof panels (Terne coating is a a zinc-tin alloy metal coating process that gives extra corrosion resistance. Other terne coatings using lead can present an environmental contamination worry from lead leachate found in roof runoff.)
Because it is harder than aluminum metal roofing, stainless steel roof panels will be more resistant to impact damage from hail, and the metal also has less thermal expansion/contraction movement than either aluminum or copper roofs.
Watch out: other grades of stainless steel (SS 304) are not recommended for use near areas of salt spray such as close to oceans. And to avoid pitting-corrosion, stainless steel roof panels are installed using methods to provide panel ventilation on both the exposed and down-facing sides.
Details about terne metal roofing are at TERNE METAL ROOFING
Sources of Stainless Steel Roofing Products
Zinc roofs are similar to copper in their durability and also similar to copper roofs in their installation procedures. But unlike copper, zinc roofs weather to a bluish-white color rather than green. Zinc roofing material, widely used in Europe, is very malleable and can be formed into intricate patterns for metal shingles.
Details about zinc metal roofing are at Zinc Metal Roofing
-- Adapted with permission from Best Practices Guide to Residential Construction.
Where to Buy Metal Roofing: Manufacturers & Metal Roofing Sources, Associations
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 Metal Roofing Materials, Methods, Standards
Metal Roofing Alliance www.metalroofing.com
-- Adapted with permission from Best Practices Guide to Residential Construction.
Continue reading at MODULAR METAL ROOF SHINGLE SYSTEM or select a topic from the More Reading links shown below.
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