TL;DR
A vapor barrier under slab is the polyethylene sheet placed over the prepared base before concrete is poured, blocking soil moisture and vapor from migrating up through the cured slab into flooring and living space. Modern practice specifies 10- to 15-mil material meeting ASTM E1745 Class A, with lapped, taped seams and sealed penetrations, since thin 6-mil poly punctures during the pour.
What it means
A vapor barrier under slab is the polyethylene sheet placed over the prepared base before concrete is poured, blocking soil moisture and vapor from migrating up through the cured slab into flooring and living space. Modern practice specifies 10- to 15-mil material meeting ASTM E1745 Class A, with lapped, taped seams and sealed penetrations, since thin 6-mil poly punctures during the pour. Skimping here shows up later as cupped wood floors, failed adhesives, and musty slab-on-grade rooms, and it is also a component of passive radon control.
Where it sits in the glossary
Vapor barrier under slab 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
License: CC-BY-4.0 — quote freely with attribution to ProFix Editorial Team / ProFix Directory.