Metal Roofing Types, Product Sources, Installation, Defects, Repairs

Index to Metal Roof System Information

There are three general types of residential metal roofing

1. Exposed-fastener Panel Metal Roofs - detailed
   
   at METAL ROOF EXPOSED FASTENER SYSTEM,
   
   also see CORRUGATED ROOFING
2. Standing-Seam Metal Roofs -
   
   see STANDING SEAM METAL ROOF INSTALLATION

3. Modular Panel Metal roofs. Details about metal shingle roofs of this type are
   
   at MODULAR METAL ROOF SHINGLE SYSTEM.
   
   Also see METAL SHINGLE ROOFS

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 [image below] 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.

1. Aluminum metal roofing,
   
   first used in the U.S. in 1890 on Philadelphia's City Hall, difficult to solder, relied on mechanical joints and slope to shed water.
   
   Details about aluminum roofing are
   
   at ALUMINUM ROOFING.
   
   Also see ALUMINUM METAL ROOFING - PRODUCT SOURCES
   
   and ALUMINUM METAL ROOFING SYSTEM PROPERTIES
   
   and CORRUGATED ROOFING
2. Aluminized Steel Roofing -
   
   see details about aluminized steel roof coverings
   
   at ALUMINIZED STEEL ROOFS
3. 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 at BARN ROOFING, METAL.
   
   and CORRUGATED ROOFING
   
   Also see STEEL & IRON BUILDING SIDING 
4. 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
   
   at COPPER ROOFING
5. Corrugated metal roofing
   
   details of iron & steel metal corrugated roofs as well as other corrugated roofing products are
   
   at CORRUGATED METAL ROOFING
   
   See the history of these materials
   
   at STEEL & IRON BUILDING SIDING
   
   
6. 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.
7. 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.
   
   Details about galvanized iron or steel roofing are
   
   at GALVANIZED STEEL ROOFS.
   
   Also see GALVANIC SCALE & METAL CORROSION
8. Galvalume®
   
   is metal roofing coated with zinc or zinc/aluminum. Details are
   
   at GALVALUME METAL ROOFING
9. 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."
10. 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.
    
    Lead 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."
11. 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.
    
    Details about lead in roofing are
    
    at LEAD ROOFING & FLASHING.
12. Stainless steel metal roofing
    
    including terne-coated (tin and zinc-coated 304 stainless steel) roof materials. Details about stainless steel roofing are
    
    at STAINLESS STEEL ROOFS
13. Steel metal roofing
    
    includes
    
    GALVANIZED STEEL ROOFS
    
    and
    GALVALUME METAL ROOFING discussed in those articles.
14. 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.)[1]
    
    Details about terne metals used on roofs, gutters, and for other building exterior components are
    
    at TERNE METAL ROOFING
15. 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 - cited in page bottom References or Citations
    
    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% iron alloy),
    • 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
    • Terne 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

Also see METALS USED IN ROOFING.

Factors Affecting Metal Roof Life and Leak Resistance

According to the US NPS,

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 ROOFING we 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 weather tight a roof will be under extreme weather. More on roof slopes is

at ROOF SLOPE DEFINITIONS.

Barn Roofing - Standing Seam or 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.

Watch out: as we illustrate in the photo below, metal roofing that is not adequately-secured at the roof edges will eventually be ripped from the roof by storm-winds.

This post and beam barn, built in Poughkeepsie, New York before 1900, demonstrates that a building can stand for a very long time provided it is protected from the weather by a good roof.

But once that roof protection is lost the building has not much remaining life. The original wood shingle roof, when worn and leaky, was covered by a light-weight standing seam metal roof.

More-recently storms have torn off a substantial part of the barn's metal roofing.

Below: post and beam details found in the same building (below) give an indication of the probable age of this New York barn when photographed in December 2021 and again in the spring of 2022 (above).

Openings through the roof admitting the weather will speed the fall of this magnificent building if the roof is not replaced.

See METAL ROOF EXPOSED FASTENER SYSTEM for details about barn roofing material, installation, fasteners, and for barn roof flashing

see METAL ROOF EXPOSED FASTENER FLASHING.

At CORRUGATED ROOFING we discuss all types of corrugated roofing products: metal and others.

Copper Roofs

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.

Also see COPPER SHINGLE METAL ROOFING - soldered metal or copper shingle roofing on flat or low-slope roofs.

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 Associates' metal roof shingle sketch (below left) provides additional details about this roofing option.

Details about metal shingle roofs of this type are

at MODULAR METAL ROOF SHINGLE SYSTEM.

Metal Shingle Roofs, Embossed, Antique

The antique embossed metal shingles (below) are found on the Justin Morrill Smith historic homestead, Vermont.

Below we see an example of a metal roof in good condition.

In contrast, below we show metal roofs in more questionable shape, beginning with a metal shingled roof on a 1910 home in Rockland County, New York, courtesy of home inspector Dovber Kahn.

Above: these shingles are separating at some of their crimp joints, risking leaks, particularly in conditions of wind-driven rain or perhaps when water backs up the roof as accumulated snow begins to melt. We also see that the roof is rusting. But before cleaning and re-painting this roof we'd suggest that an experienced metal shingle roof contractor inspect its condition to be sure that the roof is salvageable.

Mr. Kahn is a licensed home inspector in New York and New Jersey, and can be reached at Website: Kahnbhomeinspectors, Tel: 845-445-8234, Email: kdovber@googlemail.com

Watch out: it can be a serious mistake to hire a roofing contractor to inspect a roof type with which she is not very familiar. Too often the contractor is tempted to err on the safe (for them) side: condemning the roof and advising that the owner install a new and different roof covering of the sort that the contractor uses. Before doing that let's be sure that the existing roof really deserves to be condemned.

The rusted metal shingles on the church roof (Clintondale, NY) shown in our photo below demonstrate more about the history of how metal roofing was used in the U.S.

We see that the original wood shingle roof was re-roofed using metal shingles.

Quoting Grapevine Design Guidelines:

Metal roofing in America is principally a 19th-century phenomenon. Before then the only metals commonly used were lead and copper.

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 material.

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 just below and also at patents described

in this article: COPPER SHINGLE METAL ROOFING - soldered metal or copper shingle roofing on flat or low-slope roofs.

Also see MODULAR METAL ROOF SHINGLE SYSTEM.

Soldered Flat Shingle and Flat Copper Metal Roofs

Flat metal shingles with interlocking edges were produced in both steel and copper, then soldered when in place.

Usually we find these installed on flat or low-slope roofs such as at dormer insets on homes constructed in the U.S. before 1900, often in the mid to later 1800s, but on occasion even on new or newly restored homes as well.

Carson Dunlop Associates' standing seam metal roof sketch (below) includes a sketch of soldering used to connect flat metal roofing panels.

Watch out: large expanses of metal roofing with soldered connections may flex and break open the soldered joints due to thermal movement.

Details about soldered copper roofs and some suggested inspection points are

at COPPER SHINGLE METAL ROOFING - soldered metal or copper shingle roofing on flat or low-slope roofs.

Standing Seam Metal Roofs

Standing seam metal roofs were widely used throughout North America and in modern forms remain in use today as a very durable roof covering, especially if the metal coating or paint is maintained.

Carson Dunlop Associates' standing seam metal roof sketch (left) shows how sheet metal roofing is secured to the roof deck using cleats. Sections of metal roofing may be joined by

• Standing seams that are rolled and crimped
• Interlocking seams
• Battened seams
• Soldered Joints or soldered lap seams
• Flat locking metal seams.

See  STANDING SEAM METAL ROOF Installation for details about standing seam roof installation, flashing, maintenance, repair.

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.

See STANDING SEAM METAL ROOF INSTALLATION for details about standing seam roof installation, flashing, maintenance, repair.