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Guide to metal roofs: choices, installation, inspection, troubleshooting & metal roof repair procedures.
This article describes types of metal roofing products and metals: metal roof choices, installation, inspection, metal roof defects, roofing repairs, and metal roof product sources.
Page top photo, the Richard B. Fisher Center for the Performing Arts at Bard College, architect Frank Gehry.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
Metal Roofing Materials, Choices, Costs, Life Expectancy, Characteristics
Residential installations of metal roofing have more than
doubled in the past several years, and they are now estimated
to account for over 10% of residential roofs.
associated with agricultural and commercial buildings,
new metal roofing products aimed at the residential
market are designed with simplified installation systems
and offer more choices in materials, finishes, and design.
This introduction to metal roofing is adapted with permission from Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES.
The installed cost of premium metal roofing is three to four
times more than asphalt shingles, but metal roofing offers
a variety of attractive benefits:
Fire resistance of metal roofs: Many metal roofs carry a Class A fire
Low weight of metal roofs: Most metal roofing products range from
125 to 175 pounds per square. Some lightweight aluminum
shingles weigh as little as 40 pounds per square.
Wind resistance of metal roofs: Many systems have earned a Class
90 wind-uplift rating, UL’s highest rating.
Impact resistance of metal roofs: Metal roofing systems offer moderate
to excellent resistance to impact from hail, some
earning UL’s Class 4 rating.
Mold-resistant: Metal roofing resists the type of algae
and mildew growth that attacks asphalt and wood
Energy efficiency of metal roofs: In a test conducted by the Florida
Solar Energy Center, white metal roofing showed the
greatest reductions in cooling loads of all roofing
types, with 23 to 30% savings (compared to a control
home with dark asphalt shingles).
Recycled content of metal roofs: Many metal roofing products use
recycled material, ranging from 25% with some steel
products to over 90% with some aluminum modular
What is the Life Expectancy of metal roofs? Metal roofs typically carry a 30-to 50-year
Noise Transmission of Metal Roofs
One frequently cited disadvantage
of metal roofing is that it generates a noticeable noise
when struck by rain, hail, or even dropping acorns. If installed
directly to purlins with no roof sheathing, the noise
might be heard in the building interior. However, when installed
over a solid substrate, with normal levels of insulation,
the noise should not be noticeably different than with
other roofing types.
Panels laid flat on solid decking are generally
walkable. However, if panels are installed on battens,
workers should be careful to step directly over battens or to
use planking that spans multiple battens. Modular shingle
panels generally use fairly light-gauge material, but it is
stiffened somewhat by the stamped textures. In general,
modular steel panels are walkable, but aluminum ones
should be reinforced by foam inserts in sections expected
to see a lot of foot traffic.
As summarized in Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES, 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.
[Click any table or image to see an enlarged version.] Following this table is our complete list of metal roofing products.
Barn Roofing - is a synonym for exposed fastener metal roofs of aluminum or galvanized steel. Sometimes we find this roofing system used on residential properties too, though there are some questions about leak resistance of some installations. Details are atBarn Roofing, Metal.
Copper metal roofing - an early use in the U.S. in 1764 on the New York City Hall, infrequently used until late 1800's when copper supply increased, more costly, easily worked, does not need a weather-resistant coating. Details about copper roofing are atCOPPER ROOFING
Corrugated metal roofing - details of metal corrugated roofs as well as other corrugated roofing products are at Corrugated Metal Roofing
Enameled steel roofing - according to the US NPS, "Enameled steel as a building component came to this country by way of Germany at the end of the 19th century. Shingles of enameled steel were exhibited by a German industrialist at the 1893 World's Columbian Exposition.
The first American production was in 1924 by the Columbian Enameling and Stamping Company, which roofed a house in Terra Haute, Indiana, with enameled shingles.
Commercial markets developed by 1930, and enameled shingles became popular for use on service stations and chain restaurants. Except for the 2500 Lustron houses manufactured in the late 1940s, the material was rarely used in residential applications."
The NPS article includes an example from the 1929 Sweet's Architectural catalogue that describes enameled roof shingles.
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.
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."
Lead Roofing - according to the US NPS, "The earliest use of lead for roofing in this country may have been at Rosewell, an 18th-century plantation house at Whitemarsh, Virginia. It was widely used before the American Revolution for flashings, downspouts and gutters on the best buildings. In the United States, lead never achieved the popularity it had in Europe.
Installed on early Federal buildings in Washington, D.C., it failed to perform well. Expansion and contraction due to temperature changes produced fatigue, and on steep roofs the effect of gravity caused creep.In the 20th century lead found additional application as a coating for both steel and copper."
Lead-coated copper - availble and used in construction since approximately 1900, lead-coated copper does not extend the life of copper itself, rather it provides an alternative color to architectural copper applications and it avoids staining that may occur on some light colored building surfaces (masonry, limestone, stucco, light-colored wood surfaces) where copper is used for roofing, flashing, or gutters.
Watch out for possible environmental concerns with lead runoff and lead exposure hazards.
TERNE METAL ROOFING, or Terne II coated metal roofing are used where copper roof runoff or corrosion are special concerns.
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.)
Details about terne metals used on roofs, gutters, and for other building exterior components are
atTERNE METAL ROOFING
ZINC METAL ROOFS - according to the US NPS, "Rolled sheet zinc appeared in the United States in 1816, as roofing in New York and as downspouts and gutters in Baltimore. Though more than seventy houses in New York had zinc roofs by 1837, it was out of favor by 1840. The popularity of the material was cyclical in the next decades, never matching iron and steel with their various coatings."
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
The American Galvanizers Association explains why Zinc works well as a corrosion resistive coating:
Zinc, like all metals, corrodes when exposed to the
atmosphere. However, because of its ability to form
dense, adherent corrosion byproducts, the rate of
corrosion is considerably lower than ferrous materials
(10 to 100 times slower depending on the environment).
Zinc corrosion products develop naturally on the surface
as the coating is exposed to natural wet and dry cycles
in the atmosphere and are often referred to as the zinc
patina. The zinc patina acts as an additional barrier
between the steel and the environment.
In addition to the natural barrier protection of the coating
and patina, zinc also protects the base steel cathodically. - American Galvanizers Association, retrieved 20 April 2015 - see REFERENCES
This same AGA source points out that there are at least seven different types of coated or corrosion-resistant sheet metal products in current production:
Galvanized (zinc or Zn-coated)
Galvannealed (90-92% zinc / 8-10%
AL-ZN alloy: 55%
aluminum / 45% zinc
AL-Zn alloy: 95% zinc / 5% aluminum
Aluminum 100% aluminum
Aluminum based alloy: 89-95% aluminum / 5-11% silicon alloy
coating (85-97% lead/3-15% tin alloy)
Properly installed zinc roofs have a life expectancy of as much as 100 years. Factors that affect the wear and life of a zinc metal roof include: Installation zinc roofing over solid roof decking (not spaced nailers)
Avoid exposure of zinc roof coverings to acids found in some plywood roof decks
(review ROOFING UNDERLAYMENT BEST PRACTICES) or use zinc roofing products with a protective coating on the underside of the material
Use a ventilating mat between the zinc roof covering and the roof deck - see our discussion of Enkamat underlayment ventilating plastic roof underlayment
at ROOF NOISE TRANSMISSION
Metal roofs have a long history of use, although improvements have occurred in shop fabrication methods and new sealant materials. Metal roofs are available in a wide variety of rib configurations, colors, and slope configurations. Architectural systems use an underlying deck to provide structural support, while structural standing seam metal roofs provides an integral supporting frame. Structural systems can be used to retrofit an existing flat roof deck to provide improved drainage. Sealant is required at valleys, gutters, and drains, to ensure water tightness.
Workmanship of the metal roof installation, including consideration for thermal and building-related movement in the roof system
Metal roof fasteners and connectors: proper selection and installation
Metal roof joints, proper design and installation to accommodate movement and thermal changes
Choice of metal, and exposure to particular environments: salt spray, chemicals from nearby factories, high winds, other weather conditions. For example
at ZINC METAL ROOFINGwe note that in Europe some zinc roofs are expected to last 100 years.
Roof slope can affect leak resistance and life on any roofing system. Installing a conventional standing seam or modular panel metal roof on a nearly flat surface is likely to lead to leaks.
Minimum Slope Requirement for Metal Roofs
Most metal roofing systems can be
installed on slopes of 3:12 and greater and standing-seam
systems from 2:12 and greater. Special standing-seam systems
designed for slopes as shallow as
1/2 :12 require field
crimping machinery and have sealant in all seams. The
height of the ribs at seams and whether they are protected
with a sealant affect how weathertight a roof will be under
extreme weather. More on roof slopes is
at ROOF SLOPE DEFINITIONS.
Barn Roofing - Exposed Fastener Metal Panel Roofs
Below we provide photos of both curved and straight traditional metal barn roofing. Also see corrugated roofing and standing seam roofing below.
Barn Roofing? Our friend, builder, and home inspector Steve Vermilye pointed out that "barn roofing" works fine on barns where ventilation is important and a few drops of water falling on a cow are harmless.
But when we find this low-profile corrugated roofing with simple nailed seams installed over a home where occupants expect to stay dry, we are not so sure this is the best option, even if it is one of low cost.
At CORRUGATED ROOFING we discuss all types of corrugated roofing products: metal and others.
The standing seam copper roof shown below protects Ely Hall, originally the Alumnae Gymnasium, William M. Tubby, architect, 1889, Vassar College, Poughkeepsie NY.
Examples of fastening details for the installation of copper roofs to the building roof deck or structure are discussed under metal and standing seam roofing below.
See COPPER ROOFING for details about antique and modern copper roofing products.
Corrugated Metal Roofing
The patched corrugated metal roofing shown below (left) covers a pre-1900 home currently used as a parsonage in Dover Plains, NY. The modern corrugated roofing shown at right tops a gambrel-roofed barn in New England. More on roof shapes and architecture is
at ARCHITECTURE & BUILDING COMPONENT ID.
At CORRUGATED ROOFING we discuss all types of corrugated roofing products: metal and others.
Metal Shingle Roofs
The metal roof shingles at below-right found on a New York home are steel, coated with a granular material that from the ground can be mistaken for asphalt. Carson Dunlop's metal roof shingle sketch (below left) provides additional details about this roofing option.
The antique embossed metal shingles (below) are found on the Justin Morrill Smith historic homestead, Vermont.
The rusted metal shingles on the church roof (Clintondale, NY) shown in our photo (left) demonstrate more about the history of how metal roofing was used in the U.S. Here the original wood shingle roof was re-roofed using metal shingles, probably before 1900.
Metal roofing in America is principally a
19th-century phenomenon. Before then the
only metals commonly used were lead and
Tin-plate iron, commonly called "tin
roofing," was used extensively in Canada in
the 18th century, but was not commonly used
in the United States until rolling mills were
established in this country. The low cost, light
weight, low maintenance and ease of shipping
of tin plate made it a common roofing
Embossed tin shingles, whose
Grapevine Design Guidelines – Roof Design Guidelines 4.9 - 2
surfaces created interesting patterns, were
popular throughout the country in the late 19th
century. Tin roofs were often kept well-painted
in red or green to imitate the green patina of
copper. Unfortunately, few of these roofs
remain intact today.
Similar snap-together metal roof shingles made of copper are discussed
at COPPER ROOFING.
Our rusted standing seam barn roof photo (below left) demonstrates a common roofing sequence history: metal roofs were installed over worn-out wood shingle roofs as a more economical way to re-roof the building.
A second rusted standing seam barn roof is at below right, and our third standing-seam photo below shows a modern coated standing seam roof on North Henderson, the computing facility at Bard College, Annandale, NY.
Recommended distance between seams on a standing seam metal roof
Reader question: First, thank you for your excellent site. A great example of what makes up for the crappy stuff that draws so much criticism.
This is for Vermont, where our 40 by 50 Seventies ranch house needs a new roof.
We were thinking of going from asphalt to standing seam, though it's not a highly pitched roof and the studs are 20 inches on center.
Is there a recommended distance between the seams for a house like that, in a northern climate that sometimes sees heavy snowfall sometimes made heavier by subsequent rain?
Reply: Seam height vs. pitch on standing seam roofs
The spec for metal roofing seam distances is not about the horizontal distance between seams - that's pretty standard and up to the manufacturer. But the seam height above the roof surface is of interest on lower slope roofs if we want to be sure the roof won't leak. You'll see Eric's hand and mine in the photo at below left, and a standing seam metal roof clip installed to the decking at below right.
You want to discuss the slope of the roof with the roofing supplier. For the metal roof we installed atop my office/lab a few years ago, as the slope was rather low (less than 4/12) we were assured that a standing seam roof would work perfectly well (New York) provided we installed one that had taller seams. I.e. taller, not closer together, on lower slopes.
The metal roof is secured not to the rafters but to the roof decking which itself is secured to the rafters. As you may have seen, the connection of roof to deck is by clips that mount over a seam and are screwed to the deck. Then the clip is covered by the next overlapping seam cap of the next section.
That's why rafter spacing shouldn't be an issue.
Also as a metal roof is typically lighter than most other options (asphalt for example) the rafter spacing should be less of an issue than before - with respect to the weight of the roof.
There we include your question (near the end of the article) and answer it in detail.
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American Galvanizers Association, "Zinc Coatings, A comparative analysis of process and performance characteristics",
American Galvanizers Association,
6881 S. Holly Circle, Suite 108
Centennial, CO 80112
720-554-0900 | 800-468-7732
"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:
"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
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
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.
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