TL;DR
Roof underlayment is the water-shedding membrane installed over the deck and beneath the shingles or metal—asphalt-saturated felt in 15- and 30-pound weights or, increasingly, lighter and tougher synthetic sheets. It backstops the roofing against wind-driven rain, protects the deck between tear-off and covering, and is required by the IRC with laps and fastening specified by slope.
What it means
Roof underlayment is the water-shedding membrane installed over the deck and beneath the shingles or metal—asphalt-saturated felt in 15- and 30-pound weights or, increasingly, lighter and tougher synthetic sheets. It backstops the roofing against wind-driven rain, protects the deck between tear-off and covering, and is required by the IRC with laps and fastening specified by slope. Self-adhering ice-and-water membrane substitutes along eaves and valleys in cold climates, where the code demands it.
Where it sits in the glossary
Roof underlayment is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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