Moisture Problems With Rigid Insulation

A wet attic causes insulation to work less effectively.

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Homes with proper insulation typically use 30 percent to 50 percent less energy than homes with inadequate insulation in place. Insulation is used to keep heat from seeping out of your home, keeping it warm and comfortable. While there are many types of insulation, rigid foam board insulation is often used to insulate attics and basements. When installing rigid foam board insulation, moisture control is important to keep your insulation from becoming wet and ineffective.

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According to the United States Department of Energy, rigid foam board insulation can be used to insulate any part of your home. These rigid panels of insulation keep your home heat-resistant, while adding strength to the structure of your home. Rigid foam board insulation works effectively only when installed properly and homeowners take steps to control moisture in the area insulation is installed. Most rigid foam board insulation is made from polyurethane, polyisocyanurate or polystyrene. Rigid foam board insulation is applied to the framing in large sheets.


Polyurethane foam board insulation and polyisocyanurate foam board insulation are both constructed from closed-cell foam insulation materials. This type of rigid foam board insulation has a high R-value, which means it is very effective in reducing heat loss from your home. Many of these types of rigid foam insulation are available in compressive strengths, which allows it to keep its shape over time. Molded expanded polystyrene foam board insulation is more commonly referred to as beadboard. This material is easily molded to conform to any shape, making it an effective thermal barrier in tight spaces such as attics or basements. However, beadboard is especially susceptible to moisture damage, because the space between the foam beads inside the insulation can absorb moisture when wet. This makes moisture control a priority when using this type of insulation.

Effects Of Moisture

Moisture damage is one of the primary problems associated with rigid foam board insulation. When this type of insulation is exposed to moisture for prolonged periods, it begins to deteriorate. Once your rigid foam insulation begins to degrade, it no longer can provide your home with adequate thermal resistance. Areas of moisture inside enclosed spaces may also allow mold to begin to grow, which also causes damage to the structure of your home such as wood rot. Rigid foam insulation also degrades quickly when exposed to sunlight for extended periods of time.


Placing a vapor barrier in your attic or basement when installing rigid foam board insulation will help keep moisture problems at bay. Vapor barriers are thin membranelike coatings that slow down the rate moisture seeps into your home. After installing your vapor barrier, you must seal all gaps where moisture can leak into your home. Caulk all gaps to keep moisture out.

ReferencesEnergy Savers: Foam Board InsulationCalifornia Energy Commission: Tightening Up Your Home: InsulationPhoto Credit Comstock/Comstock/Getty ImagesRead Next:

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