Slideshow: Sealing a South Carolina Crawlspace

Workers from Energy One America start to lay a ten-mil poly ground cover in the crawlspace of a new house on Daniel Island in Charleston, South Carolina.

The installer fastens the poly to the block wall with pneumatic-driven nails and metal washers.

Seams in the poly ground cover are sealed with tenacious vapor-barrier tape. Gun foam fills the gap between the poly and the concrete block in this picture; for air-tightness and vapor control, the crew installs a bead of the expanding adhesive foam at the top seam where the poly meets the block wall around the entire perimeter of the crawlspace.

Penetrations where plumbing passes through the ground vapor barrier receive particular attention. This joint will be thoroughly sealed with vapor-tight tape.

Air-driven masonry nails and metal disks hold the poly ground cover to the concrete block walls at the perimeter. The crew seals the joint between the poly and the masonry using adhesive foam sealant.

A crew member installs a poly-faced fiberglass insulation blanket around the block wall perimeter of the crawlspace.

A crew member fastens the fiberglass insulation blanket to the block wall using gun-driven masonry nails with metal disk washers. The space between the top of the insulation blanket and the framing above is required by code, to allow inspection for termite tubes. Termites are a significant risk in coastal South Carolina.

Energy One America operations manager Seth Harris points out surface mildew on the floor trusses in a new house during a crawlspace sealing and conditioning job. In the South Carolina climate, mold tends to grow quickly, even in a very well-ventilated crawlspace — a strong reason to prefer a sealed, conditioned crawl. (Atmospheric humidity, not wood moisture content, is the culprit: Harris measured the moisture content of the trusses at only 16%.) Once this crawlspace is airtight and vapor-tight, and with mechanical dehumidification operating, Energy One will return to scrub away the mildew with a sanitizing cleanser. Given dry conditions, the problem should not re-occur.

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