How to Fix the Crawl Space in a Basement

Hang your work light. If your crawl space has very poor air circulation or high humidity, arrange your fan to draw air toward the outside. Remove any materials used for previous insulation and any other debris, and discard it. If the floor is dry or slightly damp, rake it as level as possible. (A chronically wet crawl space presents venting and drainage problems beyond the scope of this article.) Your goal is to make the space as clean and clear as possible.

Lay a sheet of plastic at least 6 feet by 6 feet to serve as a work area ground sheet. This will hold your supplies and keep them clean while protecting your legs from gravel and other minor debris on the ground. Move the sheet as needed.

Unroll insulation and place it between the floor joists, which form the ceiling of the crawl space. Place the vapor barrier facing outward or toward the floor of the crawl space. Staple insulation to the edges of the joists or secure it with anchors designed to span between joists.

Continue to insulate any parts of the crawl space walls with vertical wood stringers. Push insulation up against the floor joists but stop 4 to 6 inches above the crawl space floor to prevent it from getting soaked with ground water.

Cover masonry crawlspace walls with foil-covered insulating wrap instead, securing it with tape. Your goal is to join this wrap to ceiling insulation, making a cold-repelling moisture-barring surface. Seek professional advice, however, before blocking crawl space windows, doors or vents to avoid reducing necessary air circulation.

Lay permeable fabric across the entire floor of the crawl space. Anchor it temporarily, if doing so will be helpful, with bricks, rocks or scrap lumber pieces. This can keep you from disturbing the fabric as you crawl from one area to another with the covering ground sheet.

Lay heavyweight plastic ground sheeting over the entire floor. Tape it to the wall wrap with wide tape. If necessary, use the bricks, rocks or scrap lumber pieces to reinforce corners and strengthen the seal.