We bet that if you did some further investigation you would find that you have condensation on your roof and that your crawl space is damp. This is a classic case of poor or non-existent ventilation.

Proper ventilation performs two important functions: comfort control and moisture control. Living space must have fresh air to cool it in hot weather, and to remove steam, smoke, cooking odors and other indoor pollutants. Windows and natural air infiltration help to provide this ventilation, but every home also should have mechanical ventilators - bathroom exhaust fans, range hoods and dryer vents that are ducted to the outside.

Vents simply provide air interchange between interior and exterior spaces. Their effectiveness depends on the movement of air, whether from natural breezes, fans or convective currents. The most effective venting utilizes cross-ventilation.

Proper ventilation should control heat and moisture build-up in the attic, crawl space and uninsulated wall cavities. Many of the home improvement centers that sell ventilation products have step-by-step installation instructions available.