PWF Basement Techniques

Base

• The wood foundation usually rests on a 4-inch-deep layer of gravel or crushed stone applied to the bottom of the excavated area. The wooden bottom plates, large framing members that support the foundation walls, sit on this stone or gravel base. The plates should lie below the frost line, the level at which groundwater freezes during winter. Alternatively, you can apply a gravel base to the area that will support the basement floor but use concrete footings to support the bottom plates.

Drainage

• A key element of keeping a PWF free of excessive moisture involves setting up a good drainage system at the time of construction. The gravel base provides a porous material through which water can drain. A sump pump placed in the gravel or crushed stone carries water away from the foundation to a storm or sewer drain. The soil around the PWF should be graded to slope away from the structure to facilitate drainage.

Moisture Barrier

• A moisture barrier of polyethylene sheeting should start above the ground, cover the below-grade foundation walls and direct moisture down to the gravel base. From there, the sump pump system will carry it away from the foundation. The vertical joints in the sheeting should be overlapped 6 inches and caulked. The sheeting goes over pressure-treated plywood. You should also caulk the plywood for the full length of the horizontal joints to prevent any moisture from entering through those gaps.

Insulation

• Filling the cavities between the studs of a PWF wall increases the thermal efficiency of the basement. The insulation should not touch the bottom plate. A 2-inch gap needs to separate the wood and the insulating material. After installing any plumbing or electrical components in the walls, you cover the insulating material, such as fiberglass batts, with polyethylene sheeting. The wall is then ready to receive the finishing material, such as wallboard or wooden paneling.