How to satisfy both code and prevent ice dams when installing roofing drip edge
If I were to set the drip edge directly to the OSB roof deck, will this cause moisture and dry rot? Or should we first put down Ice & Water Shield, then the drip edge?
—James Hadden, Colorado, Springs, CO
The answer depends on which edge of the roof you're talking about. If it's the horizontal drip edges at the eaves, then the code says they should be nailed directly to the sheathing. The underlayment and shingles will cover that drip edge and should provide enough protection to protect it from rot.
But on the angles rakes at the gables, the drip edges should be installed over the underlayment. That will block wind-driven rain from getting under the edges of the underlayment and onto the sheathing.
In areas like Colorado that are prone to ice dams, a slightly different approach makes sense at the eaves. Lay a 6-inch strip of self-adhering underlayment, like Ice & Water Shield, over the top of the fascia and the sheathing, then cover it with the drip edge. Next, lay a full-width of the same self-adhering membrane over the sheathing and drip edge. (The code specifies that the membrane extend at least 24 inches past the exterior wall line.) That extra step satisfies both the International Residential Code and the membrane manufacturers’ installation requirements, which are focused on preventing ice-dam damage.
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