Not your father’s underlayment

With metal roofs gaining market share in both the residential and commercial construction markets, a growing number of roofing product manufacturers are offering new synthetic underlayments specifically geared to the requirements of metal roofers. Among their arguments: Metal roofs are lifetime products that need lifetime underlayments, and the higher temperatures generated beneath metal roofs require underlayments that can take the heat.
“Contractors and installers are selling metal roofs today by telling customers these roofs are lifetime products,” observes Sal Catanese, manager of underlayments for Philadelphia-based Drexel Metals Corporation, “but standard felt underlayments won’t last as long as a metal roof does. Synthetics let you sell a lifetime metal roof with a lifetime underlayment.”
For one thing, Catanese points out, felt underlayments can rip or tear when exposed to high winds and severe weather — even before the roof goes on. After the metal roof is installed, he notes, temperatures under the roof “can get pretty high so that felt, which is soaked with asphalt, can melt and stick to the underside of the roof.” As successive heat and cold causes the felt to melt and then reform, degradation of the underlayment can occur.
Synthetic underlayments avoid these problems, Catanese says. RoofTopGuard II, distributed exclusively by Drexel, is made from multiple layers of polyethylene and polypropylene and can withstand exposure to sun and weather for up to four months. After the metal roof is installed, the product is rated for temperatures of up to 260 degrees. Given its temperature performance, he says, roofers can install the underlayment without using the additional rosin-paper slip sheet required for felt.
Though synthetic underlayments cost more than felt products, Catanese says, “customers who pay for the quality of a metal roof are also willing to pay for the added value of synthetic underlayment.” Yet he believes the price differential is shrinking. “Felt is soaked with asphalt, a petroleum-based product,” he points out, “and as oil prices rise then so does the cost of felt underlayments.”
Where synthetics once cost twice as much as felt, Catanese now puts the difference at only 50 to 75 percent. And compared to the overall price of a metal roofing job, he says, the underlayment is not a major cost. Metal roofers should also look beyond the up-front cost, he points out. Because felt is soaked in asphalt, the product can be very heavy. Catanese notes that RoofTopGuard II is five times lighter than 30-pound felt, so that a five-foot-wide roll weighs only 43 pounds.
The lighter weight not only makes synthetics easier for crews to hoist and carry, but allows rolls to be manufactured in wider widths. “Felt rolls are usually three feet wide because that’s about the most weight a person can carry and handle,” Catanese explains, “but you can easily carry a five-foot-wide synthetic roll, which helps you install underlayments faster and easier,” reducing labor costs. RoofTopGuard II is also designed with a “fiber-grip” skid-resistant surface for safety, and made to maintain a waterproof seal around nail fasteners.
Though peel-and-stick synthetic underlayments are on the market, Catanese believes the jury is still out on how the adhesives will hold up over the long term. RoofTopGuard II is mechanically fastened with cap-nails driven by a standard pneumatic gun. “But in the North where snow and ice damming is a problem,” he adds, “you could use peel-and-stick products as shields around valleys and eaves, and use our product for the balance of the roof.”
Though felt underlayments are still the standard in the United States, Catanese predicts that “felt has had its day, but its market share will continue to erode.” Some     manufacturers of felt products are trying to devise performance enhancements, he notes, “but that only makes the felt more expensive and takes away from its only advantage, which is price.”

Mechanical or Peel-and-Stick
TAMKO Building Products of Joplin, Mo., offers two synthetic choices for metal roofs.  
TW Metal and Tile Underlayment, along with TW Underlayment, are self-adhering rubberized asphalt sheet membranes faced with polymer film. TW Metal and Tile is reinforced with fiberglass, while TW Underlayment comes in at 40 mils thick.
“The products are great when you need to prevent water penetration, and they can also provide secondary protection against water penetration after installation of a metal roof system,” says Dan Hollabaugh, general manager for waterproofing, industrial sales, cements, and coatings at TAMKO. By contrast, he adds, “Felt underlayments don’t have any adhesive, so water can wick underneath them. And they’re more susceptible to wind damage when they’re exposed to weather, because felt is only nailed or stapled down.”
The two TAMKO products are rated for up to 90 days of UV exposure and, after the roof is put on, can withstand temperatures of at least 245 degrees. As peel-and-stick underlayments, Hollabaugh continues, “They’re good from an installation standpoint because it requires less time and labor than underlayments you have to nail down, you don’t have to put holes in the decking.” Installers will also appreciate the textured surface which provides skid-resistance for safety.
“Alternatives to felt underlayment have been around for a long time,” Hollabaugh reports, “but in the last five years or so, interest in peel-and-stick synthetic underlayment has really taken off. Though it costs quite a bit more than felt products, sales of peel-and-stick underlayment continue to grow because people are willing to pay for proven performance.”
Two choices of synthetic roof underlayment, both made of 100 percent polypropylene, are also available from Kirsch Building Products of Simi Valley, Calif. According to president Mark Strait, the company’s Sharkskin Comp is designed for asphalt roof installations and Sharkskin Ultra for metal, slate, and tile roofing systems.
“A one-product-fits-all approach hasn’t worked well in the marketplace,” Strait explains, “and so we’ve geared Sharkskin Comp to the more price-sensitive asphalt roofing market, and made Sharkskin Ultra for the high-performance market.” The Ultra product, for example, is rated for up to 12 months of weather and UV exposure. “Last year there was a metal shortage, while in Florida people had to wait on deliveries of roof tiles,” he recalls, “and so you might need your underlayment to stand up for more than just three or six months.”
Sharkskin Ultra has also been designed with higher abrasion resistance, plus a fastening system that eliminates the need for plastic cap-nails. “When you’re putting on a metal roof, and if your underlayment is fastened with cap-nails,” Strait suggests, “it can produce visible dimples in the skin of the metal, which isn’t very aesthetic.”
For Strait, the case for synthetic underlayment with metal roofs comes down to two considerations: pre- and post-installation. In the pre-installation phase, synthetics remain solidly on the roof while felt products “can easily get torn or ripped off in high winds, so that you get water damage,” he says. In the post-installation phase, he continues, “Metal roofs often have 50-year warranties and may last indefinitely, and so a long-lasting underlayment is a necessary complement. Also, if for some reason the primary roof fails — maybe in a hurricane — synthetic underlayment can provide secondary protection from water penetration.”
Compared to the overall cost of a metal roofing system, “it doesn’t cost you that much more, proportionately, to use synthetic underlayment instead of felt,” Strait says. He agrees that asphalt-laden felt underlayment can stick and unstick to the underside of a metal roof during episodes of heat and cold, so in time the felt can deteriorate. “Also, felt is organic,” he observes, “which means that when moisture is present you can get mold.”
Like most other synthetic underlayments, Sharkskin is made to be slip-resistant. But which product on the market really offers the most walkability? “Ask your distributor for samples of different underlayment products,” Strait advises, “and before you order anything, test them in the field, particularly when they’re wetted down as in a morning dew. In a lot of markets, the choice of synthetic products is driven by pressure from distributors. But you should test the different underlayments yourself and decide what you want.”
Metal roofers can evaluate synthetic underlayments by grouping them into twos, says Strait. The products are either mechanically-fastened or self-adhesive, and are either made of polyethylene or polypropylene. “Mechanically fastened underlayment usually allows for longer exposure to sun and weather than does peel-and-stick products,” he contends. “In addition, mechanically-fastened underlayment usually costs less, installs faster, and can be removed if the homeowner decides to remodel.”
As Strait sees it, the asphalt adhesive in peel-and-stick underlayments “can dry out over time and become less elastic — and it’s still undetermined how well these products will adhere over the long term and how the adhesive will stand up to UV exposure.” In the short term, he adds, peel-and-stick underlayments may “take some time before the adhesive is fully effective, which can be a problem if you have high winds.” Further, he says, though self-adhesive products are “seen as offering better sealing around nails, is that true over the long haul?”
The adhesive itself adds weight to a roll of underlayment, Strait continues, which makes the product more difficult to handle. And compared to mechanically-fastened underlayments, peel-and-stick installation is slower “because it takes two people to keep it straight. It’s like doing wallpaper. You have to start at the eave of the roof and roll it out straight. For one thing, being on the eave of a roof with a heavy roll of underlayment isn’t the best situation. For another, if the roll gets slightly askew or buckles, you can’t pull it off the deck and start over. Instead, you have to trim the underlayment in order to compensate.”
Strait concludes that self-adhesive underlayments “aren’t designed for the entire roof” but can provide ice and water protection in areas such as valleys, eaves, and dormers. Moreover, he characterizes polypropylene is being less sensitive to temperatures and more stable than polyethylene.
“Another reason to check out samples of different products,” Strait relates, “is the fact that synthetic underlayments are still in an early stage of development. You can’t just develop a product and throw it up on the roof. Some manufacturers are less knowledgeable than others. There are a lot of new companies out there with synthetic underlayments and so I think there’s eventually going to be an industry shakeout.”
Strait advises that, despite manufacturers’ claims about high temperature ratings, roofers can encounter “a lot of marketing jargon.” He tells roofers to “make sure the product has been tested and been approved by the International Code Council and regional code bodies. Also, some manufacturers’ warranties are voided once the underlayment is penetrated — even by a fastener. So be sure and get some references from other people who’ve used a synthetic product, before you buy.” Sharkskin is rated, he says, for a softening point of 230 degrees and a melting point of 300 degrees.
“The construction industry is slow to change,” Strait believes, “but the old technology of felt is becoming more inferior to synthetics. Synthetic underlayment provides better performance and more productivity, and perhaps fewer workers comp claims because your crews aren’t lifting heavy rolls. And as oil prices go up and the cost of asphalt rises, then felt will lose its only advantage, which is price.”

Synthetic Sales Growing
Though Berger Building Products of Feasterville, Pa., brought out its Pro-Master Roof Shield UDL synthetic underlayment only 18 months ago, “sales are definitely on an upward trend,” reports sales and marketing manager Michael Pietrzak. “Even though price is always an issue in the construction industry and roofers have been using felt forever, our synthetic product is gaining awareness.”
Felt underlayment continues to enjoy a price advantage over synthetics, but Pietrzak describes the difference now as “slight” because petroleum prices are rising and asphalt-laden felt is becoming more expensive. But even at a higher price, synthetic products can save metal roofers money “by being quicker to install than felt, since synthetic underlayment is much more lightweight and therefore can be manufactured in wider rolls.”
A four-square roll of Pro-Master Roof Shield UDL weighs 11 pounds and a 10-square roll just 28 pounds, both about three times less than felt, Pietrzak says. Given the narrowing price difference between felt and synthetics, he believes roofers can now consider using synthetic underlayment for all roofing applications — whether metal, slate, tile, or asphalt. The Berger product, he continues, is anti-slip-coated for safety and UV-stabilized for up to one year of exposure. “In storm-damaged areas there can be shortages of shingles,” he notes, “and so the exposure rating is very important.”
High performance under even prolonged exposure, as well as long life after the roof is in place, are features of Titanium-UDL and Titanium-PSU synthetic underlayments from InterWrap Inc. of Mission, B.C. “Roofing products have to be really durable, since roofing construction is an extremely challenging application,” says Gary Schinning, division manager for roofing products.
“Think about what roofing jobs are like,” he continues. “Crews are walking and working on the underlayment, and the people often carry heavy loads and have to twist and turn their feet. Felt can rip and tear, or blow off in a high wind. But synthetics can take it, and are also slip-resistant to help keep workers safe.” InterWrap’s UDL product features SURE-FOOT, a nodular surface for walkability even on wet or steep roofs.
Schinning states that Titanium-UDL is six times lighter and 20 times stronger than standard 30-pound felt. A 10-square roll weighs 45 pounds, compared to 225 pounds of nominal weight for an equivalent roll of felt. “Put another way,” he points out, “you get 10 squares of coverage, for the same weight as only two squares of 30-pound felt.” Because of the light weight, plus a 48-inch width and 250-foot run length, he estimates than InterWrap’s underlayment can be installed at least 50 percent faster than felt.
“You’ve got fewer laps, cuts, and less roll handling,” Schinning relates. “Also, you don’t need a slip sheet because our product forms a barrier to air, water, and vapor. And since the roll is wider than a felt roll, you don’t need as many fasteners. All of that means you can do more jobs in less time, inventory fewer rolls, and enhance your productivity and profits.”
Titanium-UDL is mechanically fastened, while Titanium-PSU is a peel-and-stick product used in valleys, eaves, and with metal flashing for extra protection against water and ice damming. Once installed, the underlayments are rated for up to six months of UV exposure. Then after the roof is put on, the InterWrap products can withstand temperatures ranging from 70 degrees below zero, to a high of 212 degrees.
“Since the underlayment is synthetic,” Schinning notes, it’s unaffected by water, and it’s mold-free, lays flat, won’t wrinkle, and you can leave your roof uncovered without the need for tarps or immediate dry-in. And unlike felts, it doesn’t dry out, crack, or leach oils in the heat, and it doesn’t become stiff, difficult to unroll, or crack in the cold.” Titanium-UDL has also been certified under the ASTM D1970 standard for nail sealability since the product is engineered to form a polymer seal around approved nail fasteners.
Schinning acknowledges that synthetic underlayments cost about 75 to 100 percent more than equivalent felt products. “Unlike felt,” he adds, which “uses the cheapest materials and involves only one manufacturing step,” he explains, “the process to make synthetic underlayment requires several steps and costs more.” As a percentage of the total cost for a metal roofing project, however, “there’s not that much difference in total dollars to use synthetics instead of felt,” he adds. “Also, it’s been reported that labor savings can wipe out the cost difference. And besides, metal roofing customers want quality and a lifetime product.”
Those performance qualities, Schinning contends, also make synthetic underlayment a product that contractors could use under any roofing material — copper, zinc, galvanized steel, aluminum, slate, tile, synthetic tile, clay, cement, cedar shake, or asphalt. “Sales of synthetic underlayment will continue to grow,” he predicts, “and the growth will come at the expense of felt. Just as homebuilders today couldn’t imagine going back to the days before house wrap, someday contractors will use synthetics and wonder how they used anything else.”

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