At home with metal

• Photo courtesy of Classic Products Inc., Piqua, Ohio.
• Photo courtesy of Classic Products Inc., Piqua, Ohio.
• Photo courtesy of Classic Products Inc., Piqua, Ohio.

Editor's note: Following are the author's opinions. Views expressed are not necessarily those of NRCA.

Let's face it—the roofing business can be tough. Contractors who successfully set themselves ahead of the competition in terms of professionalism, quality and value are the ones who survive. Part of their success comes from the products they offer their customers. And adding residential metal roof systems as an option can help a contractor stand out from his competition.

In recent years, the metal roofing industry has seen increased opportunity for its products in the residential arena. In certain geographic regions, such as coastal and mountain areas, the use of metal roof systems is more prevalent than it has been in the past. My experience has shown me that anywhere there is an extreme climate, whether it's related to heat, wind, hail, snow or ice, increasingly more metal is being used.

The Metal Roofing Alliance (MRA) is projecting ongoing growth rates of 20 percent to 25 percent per year in terms of metal's share of the overall residential roofing market. If this is to be achieved, the metal roofing industry must continue its focus on consumer education and awareness. However, it also needs to increase its efforts in educating roofing contractors and distributors about current available products and how to correctly use those products. Perhaps the greatest opportunity lies in making sure the roofing industry knows the differences between various metal roofing products and the role those differences play in creating successful metal roof systems that meet homeowner needs. Following is some information to help you get started in the residential metal roofing market.

How metal is used

One common misconception about residential metal roofing is that most of it is being used on new construction. In fact, NRCA's annual market survey shows metal residential roofing in 2004 was 33 percent new construction, 56 percent reroofing and 11 percent maintenance and repair. If anything, metal is perhaps a little more skewed toward reroofing than the overall industry. One reason for this is that many metal roofing products have been designed with the ability to be installed over existing roofing materials. These generally include several metal shingle, shake and tile products, as well as some of the heavier vertical-seam products.

The wide variety of available product styles can be confusing. In North America, there are more than 100 metal products resembling shake, shingle, slate and tile. Because each product is proprietary, they are not intended to be used with one another. To ensure proper installation and use of a metal roof system, a basic understanding of available products is necessary.

Products

When determining what type of metal roof system to install on a home, limit the choices to products appropriate for the slope and geometry of the roof at hand. For example, most shake and shingle profiles require a minimum 3-in-12 (14-degree) slope. Some "snap lock" or "through-fastened sheet" vertical panels can be used on 2-in-12 (9-degree) or higher roof slopes but, for lower slopes, a standing-seam panel that is mechanically seamed or hand-seamed in the field is essential, such as a "double-lock" or "triple-lock" panel.

Falling into a general category referred to as "modular" products, many metal roofing products come in interlocking panels that can range in size from 8 inches by 12 inches (203 mm by 305 mm) to 24 inches by 36 inches (610 mm by 914 mm). There are a couple of ways in which designers of these modular metal roof systems allow for the expansion and contraction of the metal. Some systems are installed using expansion or sliding clips that allow the panels to "float" with thermal-induced expansion. Other products are designed with an "accordion effect" in the panels in which S-shaped folds in the metal act as accordion-style pleats that allow for movement because of expansion and contraction, therefore allowing for thermal change.

These modular products can be formed to resemble slate or fiberglass shingles, wood shakes and other deeply profiled products that resemble barrel tile or flat tile.

These products' rigidity, combined with the integral air space that exists between the metal panel and substrate, allows installation over existing asphalt shingles in reroofing applications. In fact, some of these systems even can be installed over wood shingles or shakes through the use of battens or special fastening methods. These installation methods can accommodate the thickness of existing roofing material but also help ensure fastening through an existing roof system and into the lath roof deck or substrate beneath if necessary.

In addition to specialty-profile modular panels, there are many vertical-seam products being used residentially. These products are installed on a roof from eave to ridge or vertically and parallel with the rafters. The general category of vertical-seam roofing includes various types of through-fastened corrugated sheet roofing and standing-seam products.

Through-fastened sheet roofing is available in various standard lengths and can be installed with transverse seams/end laps, but it also often is available in custom lengths to avoid end laps. However, with the exception of what are known as standing-seam shingles, which are short lengths of standing seam pre-engineered to lock together on horizontal seams, standing-seam products typically are ordered in custom lengths to match exact roof dimensions.

One critical factor to be aware of when installing all vertical-seam products is whether the manufacturer requires the panels be installed over battens or a solid deck. Although many of these products originally were installed over battens, often on agricultural applications, many manufacturers require solid decks and underlayment, particularly for residential applications. As is the case with any roofing material, familiarize yourself with a manufacturer's installation specifications and follow them as closely as possible.

In the case of custom-length through-fastened or standing-seam metal roofing products, safe transportation of the panels from the manufacturer to the job site is important. Often, job requirements call for panel lengths of 25 feet (8 m) or more.

To avoid the challenges associated with safe transportation, these products sometimes are produced on mobile rollformers brought to a job site. Many contractors purchase these machines to run panels for their own jobs, as well as for other contractors. Important aspects of this type of operation include having a reliable source for the coils of metal, keeping the rollformer in proper adjustment at all times and having an experienced machine operator. Even transporting the panels at a job site requires special knowledge because many of the panels should be carried on edge.

Metal types

The various metal roofing profiles discussed are available in different metals to achieve specific looks or attributes. Studies conducted by MRA show the predominant metal is steel, which is available in two forms—galvanized and Galvalume.™

Galvanized steel is coated with zinc for corrosion resistance. Galvalume steel is coated with a predominantly aluminum alloy, also to achieve corrosion resistance. Both galvanized and Galvalume are available in various grades. The grade is determined by the thickness of the zinc or aluminum coating applied to both sides of the steel. Under the quality standards of the Metal Construction Association Certification program, G90 is the recommended minimum grade of galvanized steel and AZ50 is the recommended minimum grade of Galvalume if it is to be painted. AZ55 is recommended for Galvalume if it is to be mill-finished or have a clear coat.

Other metals being used include aluminum, copper, zinc, stainless steel and terne. Aluminum is used for its corrosion resistance and malleability—such as its ability to be formed into detailed wood shake profiles. Aluminum roofing always has a paint finish or anodization applied to it for color and extra durability. Copper, zinc and stainless steel more commonly are used without additional coatings.

Copper is used for its durability and characteristic patina. Zinc also is used for its corrosion resistance, malleability and low-gloss gray look. Stainless steel is used to achieve a lasting, bright, silver metallic look or to meet the demands of an exceptionally corrosive environment.

Mix and match

When installing a metal roof system, it is critical all components be compatible with one another from a galvanic reaction standpoint. If not, electrolysis and corrosion can occur between differing metals and even other materials. This includes fasteners, flashings, gutters and adjacent siding materials. They must either be compatible with one another or separated from contact with one another.

As mentioned earlier, many of these metals have coatings or finishes on them with various aesthetic options. There are several grades of paint finishes, including acrylics, polyesters, siliconized polyesters and coatings known as polyvinylidene fluoride (PVDF). PVDF finishes are sold under the licensed trade names Kynar® and Hylar.® These various paint finishes almost always are applied to metal before it is formed into roofing panels. The more durable finishes will include specific warranties for fade resistance and chalk resistance, which is important to discuss with potential clients.

The paint industry recognizes the most fade-resistant pigments are inorganic ceramic pigments. These are more expensive than organic pigments and used in paint finishes that hold color better than inorganic pigments. In the case of PVDF coatings, the resin, which promotes paint adhesion, is based on fluorite and creates a tight molecular bond to hold the pigment in place, providing resistance to chalking.

Some modular steel shake and tile products, rather than being produced from prepainted metal, are coated after they are formed. This process is called post-coating and helps ensure good coating coverage on areas of metal that are drawn, or "stretched," during the rigorous forming of these products. The most common type of post-coating is stone coating, which involves ceramic-covered granules bonded to steel. Another post-coating option involves powder coating the formed panels, usually with a PVDF powder paint. These types of coatings provide textured, multi-hued looks. They create a "bridge" from fiberglass shingles to metal shingles and shakes.

The types of specialized coatings used on metal enhance what probably is metal roofing's best-known benefit—durability. Particularly with steel products, protecting the base metal from the elements with a quality coating is one way to achieve durability. But metal roofing products have other benefits, as well.

Benefits

One benefit of metal roofing is that residential metal roof systems are lightweight. Typical weights run from about 45 pounds per square for aluminum shingles and shakes to 150 pounds per square for stone-coated steel shakes and tiles. However, even at 150 pounds per square, the weights are substantially lower than those of most other roofing materials (fiberglass shingles weigh 240 pounds per square to 375 pounds per square). The low weight of metal products helps promote installation over existing roofing products and reduce overall weight on an older structure.

In addition, the interlocking nature of most metal roof systems, or the way in which noninterlocking panels are fastened to each other and a roof deck, achieves strong wind resistance for most systems. In many cases, the products have achieved a UL 90 classification under UL 580, "Standard for Tests for Uplift Resistance of Roof Assemblies," or UL 1897, "Standard for Uplift Tests for Roof Covering Systems."

Although metal roof systems may be preferred in some areas because of their wind resistance, there are other areas of the U.S. where metal is used for fire resistance. In fact, dating to the 1960s and 1970s, aluminum products resembling wood shakes—and later steel—have been used as fire-resistant roofing options in regions where a wood shake look is desired. However, the past few decades have seen metal roofing in all profiles being used for its fire safety. The 2003 International Building Code requires roof systems be tested to show fire resistance and exempts ferrous (steel) and copper shingles and sheets because of copper's inherent fire resistance. However, you should check local building codes before proceeding with metal roof system installations.

Another benefit of metal is that its coatings can help achieve a "cool" roof system. Metal coatings often stay clean and light-colored longer than the finishes on more porous or roughly textured roofing materials because the smooth surfaces don't collect dirt. To keep a surface clean, a homeowner could wash the roof with a hose on occasion. In addition, the coatings used on most metal roof systems have high emissivity by quickly releasing any absorbed heat back to the sky. Emissivity of all metal roofing is 0.75 at a minimum and can be as high as 0.9 depending on the coating.

However, technological advances have resulted in infrared-reflective pigments in coatings used on many metal roofing products. These specially treated pigments mean that, even in dark colors, high rates of total solar reflectivity can be achieved. As an example, a nonreflective dark-brown coating on metal may have a total solar reflectivity of 6 percent to 8 percent. However, once reflective pigments are introduced to the coating, total solar reflectivity will increase to 25 percent to 30 percent or more. This meets the reflectivity requirement of most cool roof initiatives by government agencies and utilities.

Additionally, the design of many metal roof systems provides a dead air space between the metal and underlayment or roof deck beneath it. This further enhances energy efficiency by stopping conductive heat transfer. According to tests conducted at the Florida Solar Energy Center, in the case of many metal products resembling shake and tile, this unvented air space has proved to be a contributing factor toward attic heat reductions of 30 percent and even more in comparison with traditional roofing materials. In the case of modular products and vertical-seam metal roofing products that can be installed over battens, there is the opportunity to create a vented air space for even greater efficiency.

An additional benefit achieved with metal roofing is recycled content. The metal used in most steel roofing is 25 percent to 35 percent recycled content. Recycled content increases to as much as 95 percent with nonferrous metals such as aluminum and copper.

With regard to environmental benefits, the sustainability of metal roofing also is a factor. Its durability reduces the future consumption of additional raw materials to produce more roofing materials. The life span of a metal roof system depends on the product. Unpainted steel roof systems may last 20 years to 30 years but can last longer if painted. Roof systems that originally have a painted or stone finish often have finish warranties of 30 years to 50 years and can be recoated for additional life. When a metal roof system does reach the end of its useful life, it is 100 percent recyclable and can be melted and turned into another metal roof (or something else) rather than disposed of in a landfill.

Most metal roof systems have the flexibility to adapt to unusual roof designs. This can include circular- or oval-shaped roofs, as well as roofs with convex or concave curves. In the case of standing-seam systems, many manufacturers offer matching "tapered" panels that are wider at the bottom than the top to accommodate round roofs. They also often offer curved panels for convex or concave rafters.

Modular panel metal roofs, on the other hand, have different ways of adapting to unique roof designs. Many shake and shingle profiles can be curved for round roofs. Additionally, modular panels, which have an exposure of 15 inches (381 mm) or less, easily will accommodate most roof curves. The important thing is to obtain a roofing manufacturer's input and assistance to determine how a job best can be handled.

Accessories

Although certain jobs with unusual shapes present challenges that may involve custom panels or flashings, manufacturers of residential metal roof systems typically offer a wide array of standardized accessories. These accessories are designed for eaves, gables, valleys, hips, ridges, pitch changes and roof-to-wall intersections. In some cases, a manufacturer may provide drawings for local fabrication of accessories as an alternative to buying preformed accessories.

Most residential eave details involve a drip edge that will direct water from a roof into a gutter or safely past the fascia.

With standing-seam roof systems, the bottom edge of each panel is hemmed to wrap around the starter or drip edge. The standing-seam panels attach to the roof deck with clips and then are fastened at the top of the panels. For through-fastened vertical panels, as well as some shake and tile profile panels that cannot be locked into a starter, a manufacturer usually will provide closure strips and a clear procedure for holding the lowest course tight to the roof.

There are various methods for handling gables, usually dictated by the exact profile of the roofing panel being installed. There are three basic valley styles used with the various types of metal roofing—a flat valley pan; one- or two-piece valley flashing; and a third valley option, often called an "open valley."

There also is a variety of methods used for closing off ridges and hips. Most vertical panels will use lineal hip and ridge caps, usually in 10- or 12-foot (3- or 4-m) lengths.

Situations such as slope changes and roof-to-wall intersections often will require custom-formed flashings to meet the exact roof shape. Manufacturers will provide suggested flashing designs, and you can bend these flashings on a portable brake or work with a local sheet-metal shop to have them custom fabricated. Skylights and chimneys also often will require special flashings though many of the major brand skylight manufacturers offer flashing kits designed to accommodate metal roofing.

With regard to skylights and chimneys, it is important to remember there should not be a large dependence on sealants. Although sealants can be used for aesthetic reasons and as backup water protection, the first line of defense with any metal roof flashing should be the flashing design. Extra security is achieved with sealant and underlayment.

Skylights should be on curbs that put them significantly above the highest point of the metal roof profile. On chimneys, the flashings should be cut into the masonry whenever possible. For roof-to-wall flashings, the flashings should be cut into or extend up behind the wall covering.

Attic vents and pipes should be handled per a roofing manufacturer's instructions. Several styles of pipe flashings are available that were designed specifically for metal roof systems. In some cases, these even will be available in matching colors.

Of course, as any experienced roofing contractor knows, just when you think you've encountered all unusual roof situations, something else comes along. In these cases, basic flashing design principles need to be remembered. It is important such flashings be designed to keep water flowing on top of the metal. However, the best-designed flashings often will feature redundant "backup" water channels beneath the roof panels for added safety and water protection. Another important thing to remember is to not create situations where roof debris, such as tree leaves, pine needles or ice and snow, may be trapped either by or in a flashing and cause water to back up the roof. Again, you should consult roofing manufacturers or The NRCA Architectural Sheet Metal and Metal Roofing Manual regarding the design of special flashings.

Ventilation

It is important to note manufacturers will have recommended procedures for ridge venting. These may involve special proprietary pieces or the use of commercially available ridge venting products. Many vertical-seam products are vented through the use of specially formed closure strips that allow airflow between the high ribs of the roof panels. Eave soffit vents are used for air intake.

Many people have a misconception that installing a metal roof system increases the need for attic ventilation. In fact, with conventional construction, attic ventilation is critical regardless of the roofing material. A metal roof system does not alter the need for proper attic ventilation.

You should choose to address ventilation issues along with roofing, bringing greater value to your customers. The important thing to remember at all times is that the cause of condensation is warm moist air contacting a cool surface. The goal of attic ventilation is to eliminate the opportunity for that to happen.

Careful installation

Residential metal roof systems require underlayment, and it is critical for three reasons. One is to keep the structure dry during the roof system installation process. Another reason is to provide redundant protection. And third is to keep condensation on the back of the roof panels from saturating roof substrates.

Although for many years, No. 30 felt was the standard underlayment beneath metal roofing, many contractors have switched to newer synthetics that are lightweight and offer more coverage per roll. And, of course, self-adhering underlayments are used when required by code. However, it is critical these products always are smooth rather than mineralized so as not to damage the back of the metal panels.

Also, be careful with foot traffic on most metal roofs. Explain to the homeowner how to safely walk on the metal panels or, better yet, leave instructions in writing for future reference.

Accessing steep-slope roof systems poses challenges with any roofing material, and metal is no exception. In many cases, ladders are secured from the ridge, and then, ladder jacks and walkboards are used to gain roof access. More conventional roof jacks can be used with many interlocking shake and shingle products, but they must be held up off the metal panels with weight-dispersing support boards. Another factor in roof staging exists with some of the batten-mounted shake and tile profiles, which can be installed starting at the top of the roof and simplify the installation process.

Most product manufacturers offer several options for installation training. This training sometimes can be done at a job site or manufacturer's location.

In the know

In the past, lack of awareness on the part of consumers and lack of education on the part of roofing contractors were major obstacles for residential metal roofing. However, the industry has responded, and anyone who wants to be involved with metal roofing—either as a property owner or a contractor—can obtain the knowledge and training they need.

Todd Miller is president of Classic Products Inc., Piqua, Ohio. He serves on the Metal Roofing Alliance's board of directors and is co-chairman for the Metal Construction Association's Roofing Council.

Tool time

With any job, having the proper tools is essential. Although that also applies to metal roofing, metal roof systems do not require a major investment in highly specialized tools.

Cutting tools usually consist of tin snips and a power shear. Cut-off guillotines are available for some steel roofing panels and can be beneficial in terms of speeding the installation process.

And though a heavy-duty brake always is beneficial, a heavy-duty portable handbrake, usually at least 8 feet (2 m) long, is important for a company that is going to be serious about metal roofing. A crew without a handbrake quickly will eat up the cost of a handbrake in trips back to the shop.

Other than cutting and bending tools, most metal roof system installations require nothing more than standard hand tools. These include a tape measure, chalk line, square, level, hammer and power screwdriver.