Concrete Foundation Walls - Water Leakage

Problem: Moisture damage to interior insulated foundation walls.

Cause: Air leakage behind insulation.

When interior insulation is applied to foundation walls, the surface temperature of the walls will decrease. When warmer humid air in the basement passes over the foundation walls, moisture in the air will condense out - sometimes resulting in puddling or staining under and out from the insulated wall section.

Solutions: Ensure that interior frame walls are air-sealed at the base and top to minimize air leakage and air circulation behind the insulated cavities.

• Install a moisture barrier / damp proofing in the interior face of the foundation wall to protect wood framing and insulation from moisture in the concrete. The barrier should extend from the base of the foundation wall to the level of the exterior grade as shown in Figure 33. Any membranes or coatings applied above grade must have a permeability of not less than 2.95 grain / ft²hr (in.Hg).

Figure 33 - Protecting Wood Framing & Insulation

• When framing interior walls, use sill gasket material, instead of polyethylene or building paper, under the bottom plate to reduce air leakage between the wood and concrete, or seal the drywall to the concrete at the base of a finished wall.
• Install an effective air barrier system, using either 6-mil (0.15 mm) polyethylene or the airtight drywall approach (ADA) to prevent air leakage. Penetrations through the air barrier, service entrances, electrical outlets, furnace vents, ventilation exhaust and intake ducting, must be carefully sealed to prevent air leakage.