New Roofing Underlayment Offers Light Weight, Good Traction

Coastal roofers may want to take a look at the newest contestant in the expanding world of synthetic underlayments: a membrane combining woven and non-woven polypropylene, with a fuzzy, slip-resistant walking surface, that calls itself "Opus Roof Blanket." The new fabric comes from Propex, a company with extensive experience in geosynthetic membranes and fiber reinforcement for concrete. One coastal roofer who approves of Opus is Jim Bennette, a custom roofing contractor who works on Cape Cod and Boston's South Shore. After trying out the new product, compliments of the manufacturer, Bennette told Coastal Contractor, "My guys loved it. It's a really good product." Some other synthetics have been more trouble than they're worth, says Bennette — "they're slippery, or they wrinkle when you lay them down. But this stuff is fuzzy, it's walkable, you can write on it, you can chalk-line it, and it lays flat. It's kind of like a totally different animal than some of the other synthetic felts on the market, I think." The International Codes specify asphalt-impregnated felt as the approved underlayment for most roofing materials, including fiberglass-asphalt shingles, metal roofing, slate, and tile. The plastic-based synthetic membranes aren't mentioned in the code. So for code acceptance as a substitute, manufacturers need to obtain an Evaluation Report from the International Code Council's Evaluation Service (ICC-ES). A number of suppliers have done that — to view the code reports, you can check the “ Reports” page on the ICC-ES site . But even with Evaluation Reports, comparing the synthetic felts with traditional asphalt paper — or even with other synthetics — can be a tricky apples-to-oranges problem. One huge advantage for the synthetics is their light weight — a roll of synthetic membrane that will cover 8 or 10 squares may weigh less than a roll of asphalt felt that can barely cover one square. Roofing can be backbreaking labor, and anything that lessens the load is welcome. But asphalt has the ability to seal nail and staple holes, at least partially. Most synthetics won't. In a 2006 article in JLC (" Synthetic Roofing Underlayments," by John Nicol — JLC 5/06), remodeler John Nicol recalls learning the hard way that "water — a lot of it — can get through the staple holes via capillary suction, also known as wicking" when synthetics are left exposed to the rain. That's why manufacturers call for cap nails to attach the products to the roof." (That's not a problem for Jim Bennette, who says, "We always fasten all underlayment with buttons, including asphalt felt.") And some synthetics can be very slippery when wet. In a 2006 JLC Online forum thread, a contractor described an encounter with a fog-slicked synthetic surface: "It was like ice and one of our guys slid down the roof and landed 20' down on the ground." [That's the hazard that Opus Roof Blanket is trying to overcome with its fuzzy slip-resistant surface. (According to Opus' product literature, Opus is the highest-friction synthetic on the market.) On the other hand, unlike asphalt felt, synthetics can be left exposed on the roof for long periods. In fact, an Opus product rep told JLC editor Dave Holbrook at the JLC Live expo in March, 2010, that Opus could be left exposed on the roof for up to 30 months. Of course, for a product that has only been introduced to the market this year and that still is only stocked in a handful of lumberyards, that claim has yet to be field-tested. And it's unlikely that most builders would consider leaving a roof unshingled for months, let alone years. Still, you can imagine a situation where you'd be glad you don't have to start over with fresh asphalt paper, just because the rain has kept you off the job for a couple of weeks. In the short term, you may not see Opus showing up in your local marketplace. However, you can order the material by phone at 877-315-6669, or try the company website: