Does Rigid Foam Insulation Sheathing Cause Moisture Problems at Windows?

Identification

• Rigid foam board insulation sheathing is often placed in attics, in basements or in walls to keep your home warm and comfortable. According to the United States Department of Energy, rigid foam board insulation sheathing reduces heat loss through structural elements such as wood or steel. Some types of rigid foam board insulation sheathing, such as beadboard, also known as molded expanded polystyrene (MEPS), can retain water if leaks develop. However, moist rigid foam insulation sheathing does not cause condensation to occur on windows. Certain types of foam board insulation provide better moisture resistance than others.

Cause

• Condensation occurs on windows when warm indoor air meets the cold glass surface on home windows. The result is a thin layer of moisture that beads on the glass. While condensation can occur on windows any time during the year, it is most common during the winter months when temperatures are low and indoor heating is used.

Effects

• When a small amount of moisture develops on windows, it may be a nuisance, but does not create enough moisture to cause problems inside homes. However, excessive amounts of condensation can lead to water stains, structural damage and mold growth. If the drywall underneath windows becomes wet and torn, the rigid foam board insulation sheathing may become saturated. According to the United States Department of Energy, wet insulation is less efficient than dry insulation and can damage your home.

Solution

• Keeping drapery closed during the night can cause condensation to occur, because drapes allow the window glass to remain cold. Open your drapes before bedtime, to reduce condensation. If condensation is heavy, consider installing energy-efficient double- or triple-pane windows. Energy Star-certified windows have a rating on the product label detailing how well the window resists condensation. This rating ranges from 0 to 100, with the higher numbers most effective in resisting condensation. Consider installing additional rigid foam insulation sheathing to warm the inside of your home and prevent condensation buildup.