Crawl Space Vapor Barrier & Dehumidifier

What a vapor barrier does

The ground under your house gives off moisture all the time, even when it looks dry. A vapor barrier is a sheet of polyethylene laid over the dirt floor to stop that moisture from rising into the crawl space and the floor framing above it.

Many older homes around Fuquay-Varina have a thin plastic sheet that has torn, shifted or been pushed aside by plumbers and pest control over the years. Some have no barrier at all.

Vapor barrier vs. full encapsulation

• Vapor barrier only: a new liner over the ground, overlapped and taped, often run partway up the piers and walls. The vents stay open. It's the lower-cost option and a big improvement over bare dirt or torn plastic.
• Full encapsulation: a thicker liner over the floor and up the walls, with the vents and openings sealed and a dehumidifier added. It does much more to control humid summer air. See crawl space encapsulation.

Liner thickness

Barriers are sold by thickness in mils. Thin 6-mil plastic tears easily when anyone crawls on it. Most crawl space contractors recommend a reinforced liner of 10 to 20 mil, especially if the crawl space is used for storage or gets regular visits from service techs.

Crawl space dehumidifiers

A crawl space dehumidifier is built to run in tight, cool spaces and drain automatically, usually to a condensate pump or the outside. Paired with a sealed crawl space, it keeps relative humidity low enough that mold and wood rot can't take hold. A regular basement dehumidifier from the hardware store isn't designed for this and usually doesn't last.

Signs you need a new barrier

• Bare dirt or red clay showing under the house
• Plastic that's torn, bunched up or full of puddles
• Condensation on ductwork or pipes
• A musty smell inside the house