Self-Adhering Roofing Membranes Are Not Foolproof

Scott Gibson

Last year we had a leaky roof replaced. Before the new shingles were installed, the contractor covered the entire roof with a sticky material he swore would keep water out. Guess what? When we get ice dams in the winter, the roof still leaks in places. What happened?

The sticky stuff you're referring to is probably rubberized asphalt that many roofing contractors use along eaves and in valleys as a hedge against leaks due to ice dams and wind-driven rain. In places where the weather can really be atrocious, contractrors often cover the entire roof with the material before applying shingles.

One side of this membrane is coated with an adhesive that sticks tenaciously to the roof deck. It's even designed to seal itself around roofing nails. The best known product of this kind is Ice & Water Shield, made by Grace Construction Products, so much so it's often generically called "ice and water." Similar products are made by CertainTeed and Tamko.

It's been so widely adopted because there's no way water should be able to get through. No leaks, ice dams or not.

But it doesn't always work out that way. Even on roofs that have been completely covered in the stuff, leaks can develop.

How come?

The most likely culprit is faulty installation. Although self-adhering membranes have helped to keep a lot of houses dry, they're not magic. When installed under the wrong conditions, or simply put on incorrectly, the sense of security they provide is fleeting.

Ice & Water Shield, for example, is designed to bond to a clean, dry surface when the roof deck, air temperature, and the membrane itself all are at least 40 degrees F. It should be applied only in fair weather. When the roofer shows up on a chilly November day and the roof deck is damp, results aren't going to be ideal.

Roofing materials, no matter what kind, should be installed so the laps shed water. That is, the roofer starts at the eaves and works his way up the roof, the top edge of each row of underlayment or shingles covered by the next. Seams that face uphill invite water penetration.

Grace recommends its membrane be applied in valleys first, then the eaves, and that metal drip edge along the eaves be applied after the membrane.

Ice & Water Shield is not compatible with some materials (flexible PVC, for instance, or even high concentrations of pitch), and in the desert Southwest, roof temperatures may require a special type of adhesive.

The list of caveats goes on. But some contractors and homeowners may believe these building materials are so good they're effective no matter how they're used. If only that were true.

There are still roofing contractors out there who are confident they can get a leak-free roof without self-adhering roof membranes. They use old school materials, like 30-lb. roofing felt and careful detailing instead. The building world survived a long time without these miracle products. The real trick is knowing what you're doing.

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