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Foundations For homeownersFree
Closed-Cell for Crawlspaces
Why closed-cell on crawlspace walls and rim stops moisture, critters, and the stack effect that makes floors cold.
4 min 2 modules
Lesson
Sealing the crawlspace with closed-cell stops the stack effect, blocks ground moisture, and keeps floors warm. Insulating the floor joists instead leaves the space cold and damp.
Key takeaways
- Closed-cell on crawlspace walls and rim seals the floor from moisture and outside air.
- Sealing the crawlspace stops the stack effect — warm air no longer leaks up through the house.
- It also blocks critters and humidity that cause musty smells and floor cupping.
Step by step
- 1Inspect the crawlspace for standing water, mold, and existing insulation.
- 2Fix any drainage or water issues before insulating.
- 3Remove old fiberglass from the floor joists if moving to wall insulation.
- 4Spray closed-cell on the crawlspace walls and rim joist to the specified depth.
- 5Add a ground vapor barrier if the floor is bare earth.
Quick checklist
- No standing water or active leaks.
- Ground vapor barrier installed over bare earth.
- Walls and rim sealed with closed-cell.
- Vents addressed per local building code.
Common mistakes
- Insulating the floor joists instead of the walls — the crawlspace stays cold and damp.
- Spraying over wet walls — the foam won't bond and traps moisture.
- Ignoring the ground moisture that defeats the wall insulation.
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