Moisture accumulation within a building structure can cause problems such as water stains, ice damage, peeling paint, wood deterioration, mold and mildew. Water forms when water vapor migrates through the structure and condenses on a cool surface.

There are three basic ways to minimize potential water vapor condensation problems in attics, floors and walls:

• Provide sufficient ventilation to reduce excessive water vapor build-up within the home;
• Ventilate building sections so that excessive water vapor is dissipated to the outdoor air;
• Use vapor retarders to limit water vapor transmission into building cavities.

Ventilation and circulation with outdoor air are the major moisture control strategies for attics and crawl spaces. In most parts of the country, passive ventilation is important for attics and crawl spaces, and mechanical ventilation is desirable for kitchens, laundries and baths. All of these strategies are designed to remove water vapor from the structure so that condensation will not occur.

Vapor retarders limit the migration of water vapors from warmer areas to the cold surfaces in walls, roof/ceilings and sometimes areas below floors. Vapor retarders reduce the amount of water vapor available for condensation.