TL;DR
Felt underlayment is the asphalt-saturated organic paper — sold as 15-pound and 30-pound rolls — stapled or nailed over the roof deck beneath shingles as a secondary water barrier and a separation layer between wood and shingle. It meets the underlayment requirement in the IRC, though synthetic sheets have largely displaced it for tear resistance and walkability.
What it means
Felt underlayment is the asphalt-saturated organic paper — sold as 15-pound and 30-pound rolls — stapled or nailed over the roof deck beneath shingles as a secondary water barrier and a separation layer between wood and shingle. It meets the underlayment requirement in the IRC, though synthetic sheets have largely displaced it for tear resistance and walkability. Felt wrinkles when it gets wet before shingling and dries flat again; 30-pound remains the choice under slate, tile, and cedar where thickness and forgiveness matter.
Where it sits in the glossary
Felt 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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