TL;DR
Synthetic underlayment is a woven or spun polypropylene or polyethylene sheet rolled over the roof deck beneath shingles or metal as the secondary water barrier, replacing asphalt-saturated felt. Rolls cover about ten times the area of a felt roll at a fraction of the weight, resist tearing around fasteners, and stay walkable when wet.
What it means
Synthetic underlayment is a woven or spun polypropylene or polyethylene sheet rolled over the roof deck beneath shingles or metal as the secondary water barrier, replacing asphalt-saturated felt. Rolls cover about ten times the area of a felt roll at a fraction of the weight, resist tearing around fasteners, and stay walkable when wet. Most products carry UV-exposure ratings from 60 days to 6 months, which matters when a re-roof gets dried in but not finished, and ASTM D8257 covers the material class.
Where it sits in the glossary
Synthetic 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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