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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
Green House or Solarium Roof Leaks
HEAT TAPES & CABLES on Roofs for Ice Dams
ICE DAM PREVENTION
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 describes galvanized metal roofing products and metals: metal roof choices, installation, inspection, metal roof defects, roofing repairs, and metal roof product sources.
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Galvanized iron or steel roofing - according to the US NPS, "Iron or steel are galvanized by coating them with zinc.
Rather than producing the simple coating created by tinplating, a rust resistant alloy of the two metals forms on the surface.
In 1839, two years after galvanizing was patented in Europe, the material was used on the roof of the Merchants Exchange in Manhattan.
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.
Our metal roof photo (above left) shows galvanized steel metal roofing used on both roof and the side of a small building in San Miguel de Allende.
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.
Though the sheet iron was hand dipped in the zinc, much as it was in tin, larger sheets were used (24 by 72 inches in the 1850s). This meant fewer joints, and when used as corrugated sheets, less supporting framing.
Even as the production of galvanized iron and steel roofing products increased, the price remained higher than that of other metals. The price differential did not shrink sufficiently for galvanized roofing to exceed tin and terneplate in popularity until the 20th century. "
Iron and steel roofing - according to the US NPS, "Both iron and steel without any plating were used for roofing. The Philadelphia home of the mill owner who rolled the first sheet iron in the United States was roofed in the material around 1794.
Also see Aluminized Steel Roofs. Aluminized steel generally outlasts galvanized steel but has largely been replaced in the market by Galvalume®.
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.
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.
Best Practices Guide to Residential Construction lists these producers and sources of metal roofing, metal roof fastening systems, and related metal roofing products
-- Adapted with permission from Best Practices Guide to Residential Construction.
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