Comparing Metals Used in Metal Roof Systems

METALS USED IN ROOFING - Types & properties of metals used in metal roofing system
- Galvanized Steel Metal Roofing System Properties
- Aluminized Steel Metal Roofing System Properties
- Galvalume Metal Roofing System Properties
- Aluminum Metal Roofing System Properties
- Copper Roof Metal Roofing System Properties
- Zinc Metal Roofing System Properties
Questions & Answers about different metal types used in metal roofing
References

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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.

A Comparison of Metal Choices for Roofing Systems

Adapted/paraphrased with permission from Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES: [Click any table or image to see an enlarged version.]

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 lists the advantages, drawbacks, compatibility, and life expectancy of galvanized steel roofing, aluminized steel roofing, galvalume, aluminum, copper, and zinc metal roofing products. Also see our separate article, A Complete List of Types & Properties of Metal Used in Roof Systems.

Table 2-10: Metal Roofing Characteristics (C) J Wiley, S Bliss

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® Metal Roofing

Aluminum Metal Roofing System Properties

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.

Also see A Complete List of Types & Properties of Metal Used in Roof Systems

Copper Roof Metal Roofing System Properties

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 (see FLASHING WOOD ROOF DETAILS under WOOD ROOF SHINGLE PROPERTIES)

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 at COPPER ROOFING.

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.

Details about galvanized metal roofing are at GALVANIZED STEEL ROOFS.

Also see A Complete List of Types & Properties of Metal Used in Roof Systems for more about galvanized steel roofing.

Galvalume® Metal Roofing System Properties

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 Roofing System Properties

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.)[1]

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

Corrugated Metal Roofing and Paneling, Stainless Steel, 82 Walker Lane, Newton PA 18940, Tel: 215-860-3600, http://www.corrugatedmetal.com/ including Stainless steel 303 machinable and corrosion resistant steel.
Euro Inox, European Stainless Steel Development Association, http://www.euro-inox.org/ publishes a Technical Guide to Stainless Steel Roofing at http://www.euro-inox.org/htm/p_5_EN.html - Quoting

Reasons for Stainless Steel in Roofing In architectural applications, stainless steel is often used because of its attractive appearance. Facades, interior cladding, lifts and escalators, handrails and parapets are some of the most typical areas of stainless steel use. The family of stainless steels, however, has more to offer than just good looks. Its technical properties make it an ideal choice for many other building applications, in which additional durability requirements are essential.

Stainless steel is an alloy containing at least 10.5 % chromium 1). This gives the steel an inherent ability to protect itself from corrosion. Chromium in the steel reacts with oxygen in the air and/or water to which the steel surface is exposed, and forms an invisible protective film of a chromium-rich oxide. If this layer is damaged, mechanically or chemically, it is spontaneously rebuilt if oxygen is present. Corrosion resistance is increased with higher chromium levels and, additionally, by adding molybdenum to the alloy. The presence of nickel improves formability and weldability. Nickel-containing stainless steels work-harden on cold forming and can thus give the fabricated part an additional structural function. The most commonly used stainless steels have a chromium content of around 17 - 18% and a nickel content of 8 – 10.5%. This is why they are known as "18/8" or "18/10". These chromium-nickel grades are called “austenitic stainless steels” Another family of stainless steels are mainly alloyed with chromium and possibly other elements like Titanium. These are called “ferritic” grades. For roofing purposes, 12 - 17% chromium grades with organic or metallic coatings can be used.

Flexospan Stainless Steel roofing and siding,PO Box 515, 253 Railroad St., Sandy Lake PA 16145, 800-245-0396, http://www.flexospan.com/ products: Flexbeam, Flexrib, Ventarib stainless steeel roofing panels.
Follansbee Stainless Steel Roofing, see http://www.follansbeeroofing.com/ and Follansbee's description of their ZT Alloy steel roofing
James River Steel, PO Box 11498, Richmond VA 23230, 800-825-0717, Email: info@jamesriversteel.com - Corrugated Stainless Steel Roof Panels, http://www.jamesriversteel.com/ - corrugated panels in stainless steel, flooring, aluminum, galvanized steel and fiberglass for industrial and architectural roofing, siding and decking.
Stainless Steel Information Center, Specialty Steel Industry of North America, SSINA, 3050 K Street, N.W., Washington, DC 20007 Tel: (202) 342-8630 (800) 982-0355 http://www.ssina.com/

Zinc Metal Roofing System Properties

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

Also see A Complete List of Types & Properties of Metal Used in Roof Systems

-- Adapted with permission from Best Practices Guide to Residential Construction.

Resources: Roofing Materials & Equipment Suppliers

Where to Buy Metal Roofing: Manufacturers & Metal Roofing Sources, Associations

Metal Roofing

Atas International www.atas.com Modular metal shingle, tile, and standing-seam panels
Classic Products www.classicroof.com Modular metal shingle panels and standing seam panels
Custom-Bilt Metals www.custombiltmetals.com Modular metal shakes and standing seam panels
Decra Roofing Systems www.decra.com Modular metal shingle, tile, and shake panels
Dura-Lok Roofing Systems www.duraloc.com Modular metal roofing shingles with granular coating
Fabral www.fabral.com Exposed fastener and concealed clip metal roofing panels
[1] Follansbee Steel Roofing, Follansbee WV 26037, Tel: 304-527-1260 800-624-6906, ZT Alloy (corrosion resistant terne-coated stainless steel roofing) - http://www.follansbeeroofing.com/
Gerard Roofing Technologies www.gerardusa.com Modular metal shake and tile panels with granular coating
Met-Tile www.met-tile.com Modular metal roof-tile panels
Millenium Roof Tiles,550 East Centralia Street Elkhorn, WI 53121,Tel: 262-723-7778, produces stainless steel roofing tiles, 50-year warranty, http://www.millenniumtiles.com
Zappone Manufacturing, website www.zappone.com/
Zappone Manufacturing, 2928 North Pittsburg St. Spokane, WA 99207 1-800-285-2677, Washington State Copper Roofing Supplier of Copper scallop shingles, copper shingles, copper bay windows, vertical walls, aluminum roof shingles

Venting Underlayments

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.

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

Also see A Complete List of Types & Properties of Metal Used in Roof Systems, and see our metal roofing home page, METAL ROOFING and see CORRUGATED ROOFING and COPPER ROOFING.

Frequently Asked Questions (FAQs) about types of metals used in metal roofing products: properties, installation, maintenance, repair

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Architectural elements: the technological revolution: Galvanized iron roof plates and corrugated sheets; cast iron facades, columns, door and window caps, ... (American historical catalog collection), Diana S Waite, available used out of Amazon.
"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.
[1] 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: support@metalroofing.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 lristau@connect2amc.com 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.
Metal Roofing, an Illustrated Guide, R.A. Knowlton , [metal shingle roofs],
Copper Roofing, by CDA
Copper Roofing, Master specifications for copper roofing and sheet metal work in building construction: Institutional, commercial, industrial, I.E. Anderson, 1961 (hard to find)
Corrugated Iron, Building on the Frontier, Simon Holloway
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:
http://www.nps.gov/history/hps/tps/roofingexhibit/metals2.htm
"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:
http://www.nps.gov/history/hps/tps/roofingexhibit/metals.htm
"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:
http://www.nps.gov/history/hps/tps/roofingexhibit/roofingtoday.htm
"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:
http://www.nps.gov/history/hps/tps/briefs/brief04.htm
"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:
http://www.nps.gov/history/hps/tps/briefs/brief16.htm
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
NRCA - National Roofing Contractors Association - http://www.nrca.net/, 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018-5607, Tel: (847) 299-9070
ASTM - ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, 19428-2959 USA The ASTM standards listed below can be purchased in fulltext directly from http://www.astm.org/
NRCA - National Roofing Contractors Association - http://www.nrca.net/, 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018-5607, Tel: (847) 299-9070
UL - Underwriters Laboratories - http://www.ul.com/
2600 N.W. Lake Rd.
Camas, WA 98607-8542
Tel: 1.877.854.3577 / Fax: 1.360.817.6278 E-mail: cec.us@us.ul.com

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Metal Roofing, an Illustrated Guide, R.A. Knowlton , [metal shingle roofs],
Problems in Roofing Design, B. Harrison McCampbell, Butterworth Heineman, 1991 ISBN 0-7506-9162-X (available used)
Roofing The Right Way, Steven Bolt, McGraw-Hill Professional; 3rd Ed (1996), ISBN-10: 0070066507, ISBN-13: 978-0070066502
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