Living · 6 pages · 12 min
Why a vapor barrier has a warm side
The sheet goes on the warm side so vapor does not condense inside the wall.
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From the opening
A vapor barrier, or a vapor retarder, slows water vapor moving through a wall. In a cold climate it belongs on the warm side, because that is where the vapor is, before it can reach a cold surface inside the wall and condense. The opening covers vapor driven toward the cold, why the sheet is not a raincoat, and air leaks versus slow diffusion.
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Inside
- Vapor driven toward the cold
- Why the sheet is not a raincoat
- Air leaks versus slow diffusion
- When the warm side flips
- Where the idea stops applying
- A distinction worth keeping
Sources
- Warm-side vapor retarders in cold climates
- Condensation when vapor meets cold sheathing