Metal Roofing Underlayment

Metal Roofing Underlayment

Metal is the fastest-growing segment of the American roofing market. It is durable, wind- and fire-resistant and practically maintenance-free, but it must be installed properly with an appropriate metal roof underlayment. Metal roof installation typically requires specialized tools and skills. However, the options and installation process for metal roofing underlayment are largely the same as shingles or other roofing materials, though you may need one extra layer.Preventing Ice DamsTo prevent ice dams, start your metal roofing underlayment with a layer of ice guard, also known as ice and water shield. It forms part of the metal roof underlayment over the eaves. It should extend about two feet up the roof from the top edge of the overhang.Start installing the ice guard by snapping a chalk line 35 ½ inches up from the edge of the roof, and laying the ice guard along the line. This will give the 36-inch ice guard a half-inch overhang from the eaves. If necessary, add a second strip of ice guard material.Underlayment OptionsThe next part of a metal roof underlayment is typically a layer of felt paper, or building paper. It can help keep leaks out of the attic, and it provides a little bit of insulation. Local building codes may specify a certain weight of felt paper, but 30-pound paper is usually a good bet. Metal roofing underlayment is unique in requiring an extra slip sheet layer, which is typically red rosin paper. The slip sheet helps keep the metal from sticking to the felt paper while installing the roof.There is also another option for metal roofing underlayment. New polymer underlayments sheets are thinner and easier to work with than layers of tar paper and rosin paper. The sheets are strong, waterproof and slick, so they can replace both of the other underlayment layers.How to InstallInstallation of either type of metal roofing underlayment is fairly straightforward. Add strips of felt paper or polymer underlayment horizontally across the roof, making sure to overlap the layers by at least four inches. Staple the ends of each strip, and once per square foot in the middle of the strip. Where two parts of the roof meet in a valley, overlap the metal roof underlayment generously.Proper metal roof underlayment is important for keeping the attic dry. It is largely the same as the underlayment for other roofing materials, but may require an extra sheet to ease roofing installation.Author Steve Graham is an expert on green building who writes for several home improvement publications. He’s full of great, practical home improvement answers, and incidentally, he’s pretty funny – so send him a message.

Metal Roofing Underlayment

You are here >> PRODUCTS > Accessories > Underlayments ATA-Shield Underlayment ATA-Shield is a self-adhering underlayment designed specifically for use under metal roofing. This membrane is well suited for use where a water resistant barrier is required. It is formulated to withstand the high heat environment generated by some metal roofing systems. ATA-Shield is composed of an unreinforced polymer-modified bitumin material adhered to the underside of a polymer-coated synthetic woven material. Roll Size: 3’ wide by 72’ long Membrane is 45 mils thick Split/Perforated release backing film aids in easy positioning of sheets to maintain proper line. Material is packaged in a roll of approx. 200 sq. ft. Spec Data ATA-Guard Underlayment ATA-Guard is a highly engineered, mechanically attached, coated woven synthetic roofing underlayment for sloped roofs. It can be used under all types of primary roofing materials and is approved as an alternative replacement for Type 15 or Type 30 asphalt roofing felt. ATA-Guard is 5 times lighter and 25 times stronger than 30# asphalt. ATA-Guard is 100% asphalt free, reinforced underlayment. Advanced polymers are combined to produce a film that is unaffected by water and resistant to UV for up to 6 months. 48” wide by 250’ long Material is packaged in a roll of approx. 1000 sq. ft. Nominal thickness of 30 mils Spec Data

Metal Roofing Underlayment

ATA-Shield Underlayment ATA-Shield is a self-adhering underlayment designed specifically for use under metal roofing. This membrane is well suited for use where a water resistant barrier is required. It is formulated to withstand the high heat environment generated by some metal roofing systems. ATA-Shield is composed of an unreinforced polymer-modified bitumin material adhered to the underside of a polymer-coated synthetic woven material. Roll Size: 3’ wide by 72’ long Membrane is 45 mils thick Split/Perforated release backing film aids in easy positioning of sheets to maintain proper line. Material is packaged in a roll of approx. 200 sq. ft. Spec Data ATA-Guard Underlayment ATA-Guard is a highly engineered, mechanically attached, coated woven synthetic roofing underlayment for sloped roofs. It can be used under all types of primary roofing materials and is approved as an alternative replacement for Type 15 or Type 30 asphalt roofing felt. ATA-Guard is 5 times lighter and 25 times stronger than 30# asphalt. ATA-Guard is 100% asphalt free, reinforced underlayment. Advanced polymers are combined to produce a film that is unaffected by water and resistant to UV for up to 6 months. 48” wide by 250’ long Material is packaged in a roll of approx. 1000 sq. ft. Nominal thickness of 30 mils Spec Data

Metal or tile is usually selected for architectural or aesthetic reasons. Such premium, architectural roofs are often customized to the building. It makes sense to use a premium underlayment beneath a premium roof. Also, the cost of labor for installing a roof can easily exceed the cost of materials. The additional cost for premium underlayment compared to conventional roll roofing is minor in comparison to the installation cost of the entire roof. These considerations favor the use of premium underlayments beneath metal and tile. Mod Bit Problems Modified bitumens have been used as underlayments for metal roofs in the past, but there were several drawbacks associated with them. The first has to do with the high temperatures that are reached beneath a metal roof. In direct sunlight these roofs become quite hot, and this heat is conducted to the underlayment. Aluminum or copper roofs, and dark-colored painted steel roofs, can be hot enough to cause SBS-modified bitumen to melt and drip down the side of the building. In metal roofing applications, it is critical that the underlayment used must have the ability to withstand high temperatures. Also, the SBS-asphalt blend must remain stable at these temperatures.

Structural metal roof panel systems are designed to span structural supports without requiring a structural deck.  Hence, they do not typically include roof underlayment since the installation lacks a continuous substrate or deck to support the underlayment material. For architectural metal roof panel systems, a roof underlayment is required to help control water leakage through the roofing system during heavy rain storms or under snow melting conditions. Upgraded roof underlayment is often specified in cold climates for additional protection against ice dam leakage, while high temperature underlayments are designed for use in high temperature environments where the in-service temperature can reach temperatures as high as 240ºF.Typical underlayment materials include:

Felt Underlayment The traditional and most common material used for roof underlayment on a steep-slope metal roof is non-perforated, asphalt-impregnated felt underlayment. There are several types of felt underlayment including both organic reinforced and inorganic reinforced. Compared with organic reinforced felt underlayment, inorganic, glass-fiber- reinforced felt underlayment usually lies flatter and stands up better than the organic kind.

Experience shows that a polymer surface underlayment is the best choice for use under large metal roofs, particularly in commercial applications. The polymer provides adequate slip resistance for installers, yet it easily slides beneath the metal roofing, and it is too soft to abrade the metal. At the same time, the smooth polymer surface provides better contact with the metal roof, improving heat conduction from the roof to the deck, which helps to reduce the peak temperatures. This combination of polymer surface and compound stability in one premium, self-adhering membrane results in a trouble-free underlayment for metal roofs. Vapor Barrier Often, metal roof systems that fail due to corrosion actually rust from the inside out, the result of condensation on the metal’s underside. One way to prevent this is to cover the entire roof deck with a premium underlayment, which prevents moisture from forming beneath the metal.
Metal Roofing Underlayment

Metal is the fastest-growing segment of the American roofing market. It is durable, wind- and fire-resistant and practically maintenance-free, but it must be installed properly with an appropriate metal roof underlayment. Metal roof installation typically requires specialized tools and skills. However, the options and installation process for metal roofing underlayment are largely the same as shingles or other roofing materials, though you may need one extra layer.

The GCP roofing underlayments portfolio provides a number of benefits that competing products cannot provide. Our self-adhered roofing underlayments are designed to provide strong adhesion to the roof deck, superior watertight laps, and the highest quality seal around roofing fasteners. Selecting GCP roofing underlayment products for re-roofing and new construction projects helps avoid leaks, costly damage and call-backs.

The major difference among these various types of underlayments is not immediately visible because it involves the compound stability. The polymer surface self-adhering underlayment was specifically formulated to provide high-temperature stability up to 260 degrees F as measured by ASTM D-5147. This high softening temperature is important for metal roofing, which will be explained in detail further on. Photo courtesy of Tarco Roofing Co.Membranes Under Metal Metal roofs, though they often provide many decades of trouble-free service, are not immune to leaks. Wind-blown rain can make its way under metal shingles and unsealed standing-seam metal roofs. Ice dams force open channels that allow water under the metal skin. Metal roofs also can be compromised by installation errors, accidental penetrations, foot traffic, corrosion or stresses due to thermal expansion.