Can I Put 4 Mil Plastic Over Fiberglass Insulation in Bathroom Walls?

Identification

• A vapor barrier is important in keeping your fiberglass insulation from becoming wet. Bathrooms are areas of high moisture and often have moisture seeping through the walls. Vapor barriers are usually coatings or barriers such as plastic sheeting. According to the United States Department of Energy, 4 to 6 mil polyethylene sheeting will provide an effective moisture barrier.

Effects

• Failing to place a vapor barrier over your fiberglass insulation may allow moisture to saturate your insulation. Wet insulation is less effective in reducing heat loss through your bathroom walls. When your insulation becomes wet, mold may begin to grow. Once mold growth occurs, you may experience adverse health effects such as wheezing, coughing or hives. Mold growth on your insulation may eventually deteriorate the drywall and require repair.

Installation

• After installing your fiberglass insulation, place a 4 to 6 mil plastic sheet over it. Staple the plastic sheeting to the ceiling framing and wall to keep it in place. Repair any holes or tears in your plastic sheeting to keep moisture from coming through the holes.

Considerations

• After you have installed your insulation and vapor barrier, the walls can be finished with drywall. Painting your bathroom walls will also provide another vapor barrier. The United States Department of Energy states that most paints are effective vapor barriers. When selecting a paint to use as a vapor barrier in your bathroom, choose a glossy acrylic paint for maximum protection. Apply multiple layers of paint to your walls to keep moisture from seeping through.