What Is Roof Underlayment?
Underlayment is the secondary water barrier installed over the roof deck before shingles. Traditional asphalt-saturated felt (15 lb or 30 lb) is inexpensive but absorbs moisture, wrinkles, tears in wind, and degrades quickly in Texas heat. Synthetic polymer underlayments are lighter, far stronger, more heat-stable, and safer to walk; a single synthetic roll can cover several times the area of a felt roll. The installed cost difference on a typical Austin roof is small - usually a few hundred dollars - against a system meant to last 25-30 years, which is why synthetics have become the standard on quality replacements. Underlayment matters at claim time too: it is a line item in an insurance scope, and matching underlayment lifespan to shingle lifespan is basic good practice. Horizontal courses should overlap several inches, with extra protection at eaves, valleys, and penetrations.
Also Known As
These are the search terms and phrases that commonly refer to this topic, so you can find it however you describe it.
Related To Roof Underlayment
A tile roof usually leaks because the underlayment beneath the tile has failed, not because the tile did - the tile is the armor, the underlayment is the actual waterproofing, and it wears out decades before the tile.
The rule of thumb for where membrane replaces plain underlayment: anywhere water concentrates or slows - valleys, penetrations, low-slope sections, and roof edges - because those are the spots that leak first.
The shingles are the layer you see and the underlayment is the layer that saves you: shingles shed most of the water, and everything they miss under wind-driven rain is the underlayment's problem.
Questions about Roof Underlayment?
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