Galvanized Metal Roofing Materials, Choices, Costs, Life Expectancy, Characteristics
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.
G-90 galvanized steel is typically warranted against
corrosion for 20 years under normal conditions.
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
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.
Iron replaced slate on the White House in 1804. Because it was available in large sheets, rather than the small sheets used for plated material, it required fewer joints. Some manufacturers produced factory painted material, but late19th century accounts indicate that paint was an inadequate defense against the corrosive effects of the atmosphere in industrial regions."
Galvalume®: Metal Roof Products Similar to Galvanized Roofing
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.
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.
Galvalume steel is an ideal roofing material because of its strength, extraordinary outdoor corrosion resistance and longevity. Steel roofing used in residential applications today is metallic coated with either Zinc (G90) or Zinc/Aluminum (AZ50) to provide the corrosion resistance homeowners desire. Steel roofing is strong and therefore gives higher wind uplift resistance and a broader range of application than other roofing materials.
As a result, an installed steel roof system has a broader range of price levels and products than many other kinds of metal roofing. Steel roofs have passed the UL 90 wind tests due to their strength and weight. For additional test results, visit www.fsec.ucf.edu to view the reports done at FL Solar Energy Center in their Flexible Roofing Facility.
Steel Roof ShingleToday's quality steel roofing offers excellent rust protection as well. Galvanized steel roofing is available painted, aggregate-coated, or with a mill or bare finish. Unlike conventional non-metallic roof systems, Galvalume steel roofs won't crack and peel when subjected to the sun and weather.
Frequently Asked Questions (FAQs) about galvanized metal roofing systems, inspection, installation, leaks, coatings, maintenance, repair
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"Choosing Roofing," Jefferson Kolle, January 1995, No. 92, Fine Homebuilding, Taunton Press, 63 S. Main St., PO Box 5506, Newton CT 06470 - 800-888-8286 - see http://www.taunton.com/FineHomebuilding/ for the magazine's website and for subscription information.
 Follansbee Roofing, Follansbee WV 26037, Tel: 800-624-6906, website: www.follansbeeroofing.com and http://www.follansbeeroofing.com/products/TerneII.aspx Quoting Follansbee on TerneII properties:
Follansbee Steel is the only manufacturer of a pre-painted or natural Terne roof and is a leading supplier of metal roofs for new and retrofit commercial, institutional, residential and historic preservation projects.
Terne II - Classic Terne-Coated Steel
... is a new and improved version of historic Terne metal, ... Terne II has improved capability for resisting corrosion in all environments ... also has excellent formability, solderability, and affinity for paint ... without compromising mechanical characteristics. It can be used in flatlock, standing seam, vertical wall designs and virtually any other application in which original Terne has been used. It is strong and ductile, having high yield and tensile strengths as well as workability. This new material can easily be formed with conventional roofing tools.
With Terne II roofing, it is advisable to paint the material as soon as conditions permit. Oxide formation is slower than with the original Terne and the wait for proper painting conditions provides substantially less risk. The new material is coated with Follansbee's new ZT® alloy, a combination of zinc and tin. This coating is designed not only as a barrier but also to be anodic to the steel substrate and reduce the potential for oxidation before painting.
The traditional oil-based paints long required on original Terne are not recommended for application on Terne II. Follansbee's Rapidri paint with its faster drying time and ease of application is much superior to the old painting system. The Rapidri acrylic paints are aesthetically pleasing while offering enhanced durability and color retention. ...
Metal Roofing Alliance, E. 4142 Hwy 302, Belfair, WA 98528, Telephone:(360) 275-6164, Customer Support 410-534-6900, Email: email@example.com,
Website: www.metalroofing.com. Quoting:
The Metal Roofing Alliance was formed in 1998 by a small group of forward-thinking metal roofing manufacturers with the main goal of educating consumers about the many benefits of metal roofing. Since our inception, we've shown millions of people just how beautiful, durable and money-saving metal roofing can be for them. Over the years, our membership has grown to include paint companies, material suppliers, industry publications and more. Be sure to take advantage of all of the great resources our members offer.
The Metal Initiative, 4700 W. Lake Ave., Glenview, IL 60025, P:847.375.4785 Website: www.themetalinitiative.com/, Email: Louise Ristau firstname.lastname@example.org Quoting:
The Metal Initiative is a coalition of manufacturers, individuals and associations that have come together to provide information on the features and benefits of metal in construction. Carrying its message of metal primarily to the professional building owner community, The Metal Initiative seeks to gather and disseminate useful information for decision-makers.
Problems in Roofing Design, B. Harrison McCampbell, Butterworth Heineman, 1991 ISBN 0-7506-9162-X (available used)
Grapevine Design Guidelines - Web Search 07/12/2010
"Copy on file as - /roof/Asbestos-to-Zinc_Metal_Roofing_NPS.pdf - From Asbestos to Zinc, Roofing for Historic buildings, Metals - ", Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
"Copy on file as - /roof/Asbestos-to-Zinc_Metal_Roofing_NPS_3.pdf - From Asbestos to Zinc, Roofing for Historic buildings, Metals-part II, Coated Ferrous Metals: Iron, Lead, Zinc, Tin, Terne, Galvanized, Enameled Roofs - ", Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
"On file as /roof/Asbestos-to-Zinc_Metal_Roofing_NPS_2.pdf - From Asbestos to Zinc, Roofing for Historic buildings, Metals- Roofing Today - ", Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
"Copy on file as - /roof/Roofing_Historic_NPS.pdf">Roofing for Historic buildings - ", Sarah M. Sweetser, Preservation Brief 4, Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
"Copy on file as - /exterior/NPS_Preserv_Brief_16_Subs_Mtls.pdf">The Use of Substitute Materials on Historic Building Exteriors - ",
Sharon C. Park, AIA, Preservation Brief 16, Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
ARMA - Asphalt Roofing Manufacturer's Association - http://www.asphaltroofing.org/
750 National Press Building, 529 14th Street, NW, Washington, DC 20045, Tel: 202 / 207-0917
"Metal Roofing: 'Fixing' for Thermal Movement [ copy on file as /roof/Metal_Roof_Movement_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 72, NRCA
"Metal Roof Systems: Design Considerations for Snow and Ice [ copy on file as /roof/Metal_Roof_Snow_Ice_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 74, NRCA
"Steel [Roof] Decks: Issues for the 1990's [ copy on file as /roof/ Steel_Roof_Deck_Corrosion1_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 74, NRCA
"Steel [Roof] Deck Corrosion Bulletin, NRCA [ copy on file as /roof/Steel_Roof_Deck_Corrosion_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 58, NRCA
"The Many Aspects of Metal [Roof] Shingles [copy on file as Metal_shingles_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] NRCA
Cedar Shake & Shingle Bureau, CSSB, U.S.: Sumas, WA 98295-1178, Tel: 604-820-7700, In Canada:
Cedar Shake and Shingle Bureau #2 - 7101 Horne Street, Mission, BC V2V 7A2 Tel: (604) 820-7700, E-mail: email@example.com , website: http://www.cedarbureau.org/
Forest Products Laboratory, US FPL, One Gifford Pinchot Drive, Madison, WI 53726, Tel: (608) 231-9200, Email: firstname.lastname@example.org, website: http://www.fpl.fs.fed.us/
NRCA - National Roofing Contractors Association - http://www.nrca.net/, 10255 W. Higgins Road, Suite 600,
Rosemont, IL 60018-5607, Tel: (847) 299-9070
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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