TL;DR
A vapor retarder is any material layer, polyethylene, kraft facing, special membranes, or even certain paints, installed in a wall, ceiling, floor, or crawl space to slow the diffusion of water vapor into assemblies where it could condense. Codes class them by permeance and prescribe placement by climate zone: toward the heated interior in cold climates, often omitted or vapor-open in hot-humid ones.
What it means
A vapor retarder is any material layer, polyethylene, kraft facing, special membranes, or even certain paints, installed in a wall, ceiling, floor, or crawl space to slow the diffusion of water vapor into assemblies where it could condense. Codes class them by permeance and prescribe placement by climate zone: toward the heated interior in cold climates, often omitted or vapor-open in hot-humid ones. The recurring field mistake is doubling them up, poly inside plus impermeable sheathing outside, which traps any moisture that gets in and rots the assembly from within.
Where it sits in the glossary
Vapor retarder 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.