Should I Replace a Wet Vapor Barrier in Crawlspace Before Insulating Floor?

Crawlspace Conditions

• Because crawlspaces sit part or all the way underground, moisture from the soil accesses area walls and floors. In open-vent spaces with dirt floors, you should cover walls and floors with a vapor barrier and fill ceiling, or subfloor joist cavities with insulation. Materials used as vapor barriers include rigid foam and fiberglass roll coverings. Concrete flooring also can act as a vapor barrier, although wall surfaces still will require covering. While the term “wet vapor barrier” implies vapor cannot seep through, these materials only reduce the amount of vapor entering a crawlspace. For closed-vent crawlspaces, vapor barrier protection along the floors and walls can create a sealed environment, although extensive caulking, stapling and taping of barrier materials is necessary.

Condensation

• Replacing a wet vapor barrier and eliminating the source of moisture helps reduce the likelihood of moisture re-entering crawlspace areas. Moisture build-up results from temperature differences between the inside and outside of a crawlspace. Soil temperatures average around 55 to 60 degrees on a continual basis, so when temperatures rise in the summer and warm air collides with cool crawlspace surfaces, condensation forms. Leaving a wet vapor barrier intact will defeat the purpose of that barrier as moisture will continue to enter through crawlspace floors or walls.

Vented vs. Sealed Crawlspaces

• Ideally, sealing off a crawlspace can prevent cold and warm air from colliding and prevent moisture from developing. On the other hand, venting reduces moisture build-up from dirt floors and unprotected foundation walls in cases where no vapor barriers are in place. Whether sealed or vented, a wet vapor barrier indicates a moisture problem exists and will only get worse if left unattended.

Insulation Effects

• The effects of insulating a crawlspace depend on the condition of the insulation material and the moisture levels in the area. Insulation materials contain small spaces that block cold air from entering through a building subfloor. When moisture exists, both air and moisture gets trapped inside insulation materials. The insulation then takes on weight and eventually falls out of subfloor cavities. In addition, wet insulation materials tend to breed mold and mildew. So, replacing wet vapor barriers will help reduce moisture build-up, but finding the source of moisture leaks can resolve the problem once and for all.