February 2009

Keeping water out

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Self-adhering underlayment can serve as a secondary water barrier

by Steve A. Ratcliff
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Reeling from more than a decade of powerful hurricanes dating to the devastation caused by Hurricane Andrew in 1992, Florida enacted the nation's toughest building rules in 2007. Among them was a requirement that self-adhering underlayment be installed with all new and replacement steep-slope roof systems.

Some of those rules were revised in 2008, including a rule that makes self-adhering underlayment optional rather than mandatory. As could be expected, there was an initial surge in demand for self-adhering underlayment following the initial rule's passage, but what is surprising is the continued strong demand after the rule was modified.

Specifically, Section 201.2 of Rule 9B-3.0475 (Hurricane Mitigation Retrofits For Existing Site-Built Single Family Residential Structures) describes options for a "roof secondary water barrier for site-built single family residential structures."

Adopted by the Florida Building Commission in October 2007, the rule was quite stringent, mandating that roofing contractors either cover all joints with a minimum 4-inch-wide strip of self-adhering polymer-modified bitumen tape applied directly to sheathing or decks or cover entire roof decks with approved self-adhering polymer-modified bitumen cap sheets. The rule was relaxed in March 2008 to allow other options, including covering the entire roof deck with "an approved asphalt impregnated 30# felt underlayment installed with nails and tin-tabs as required for the HVHZ" with no additional...

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