Most roofers only install self-adhered, "peel-and-stick" underlayment membranes on eaves and valleys. Of course, there's an argument for installing self-adhered over the entire roof deck in some climates and beneath some high-ticket roof claddings.
On the Eastern seaboard, for instance, hurricane-force winds have been known to strip away roof shingles, leaving bare, often leaky sheathing that's vulnerable to wind-driven rain.
As with most storm-related issues, Florida has taken the lead in addressing this one. The 7th Edition of the Florida Building Code, which became law in 2020, includes provisions for roof underlayment that apply to new construction as well as to re-roofs. Florida roofers now have three choices.
1. Use two layers of mechanically attached underlayment.
2. Use one layer, but only after taping all seams in the sheathing.
3. Cover the entire roof with a self-adhered membrane.
The best-quality choice is obviously the self-adhered, but some homeowners may balk at the cost. Fortunately, there are financial incentives. That's because self-adhered is the most effective way to satisfy the roof standard set by the Insurance Institute for Business & Home Safety's Fortified Home program. Doing so can qualify homeowners for discounts on wind and water damage insurance.
While the Florida code and the insurance industry are focused on mitigating storm damage with all roof types, at least two claddings need a sealed roof deck even outside of Hurricane Alley. We're talking about tile and metal.
Tile is popular across the Southern U.S., from the East Coast to California, and is also used on some custom homes in the North. But despite it being a high-end cladding, it's not completely watertight. It leaks. The real watershed on a tile roof is the underlayment, and since clay tile has a lifespan of about 75 years, you need the longest-lasting, highest quality underlayment possible. You need a good self-adhered.
Metal roofing is watertight, but it also lasts 50 years or more. Like tile, it needs to be installed on a good self-adhered membrane. However, metal poses another problem—it gets really hot in the sun. That means you need the right kind of self-adhered.
If the underlayment beneath a metal roof isn't rated for high temperatures, the adhesive can soften and drip out at the eaves. But the problem goes beyond the mess you'll have to clean up. Loss of adhesive means the underlayment's long-term performance will also be degraded. We recommend upgrading to High Temperature "Ice & Water" for all metal roofs and darker tile and even asphalt systems.
If you're installing an asphalt shingle roof that will only have self-adhered in the eaves and valleys, it's essential to use products of equivalent quality from the same manufacturer. That's particularly important on a custom home, where the roofer and contractor need a high-quality system they can warranty, such as the GAF Golden Pledge Warranty.
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