Crawl Space Encapsulation, Explained Without the Brochure

Bare soil is a moisture source all summer. A heavy ground cover, seams taped, piers sealed, edges run up the wall, cuts that source off. The joists above stop getting a steam bath. Surface mold that was feeding on that humidity can be cleaned and is less likely to return.

Plastic that is wrinkled into ponds, unsealed at the pier, or laid over standing water is a costume. We will not install that and call it encapsulation. If the floor of the crawl is a puddle, drainage comes before polyethylene.

Old advice said to vent crawls. In a humid July, those vents often import wet air onto cooler joists, which is how you grow a crawl that 'breathes.' For many houses here, closed vents plus a ground cover plus a small dehumidifier or a little conditioned air works better. We meter before we recommend it. A house with a true bulk-water problem through a hillside wall may still need that water managed outdoors.

Do not close vents and leave a dryer venting into the crawl. We find that more often than you would think, especially in additions.

Fallen, wet batts come out. New insulation, if you still want it, usually belongs at the walls of a sealed crawl or in a plan your insulator designs — not as soggy fiberglass stapled to a damp sill. We price ground covers by the square foot after we see rocks, piers, and access.

Encapsulation does not replace joist cleaning if the wood is already colonized. Sequence: stop liquid water, clean the wood, then cover the soil, then control the air. Skipping the middle step leaves mold food above a nice white floor.