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Q:  What's the best way to dry out my basement in the summer? Would it work to open a window down there or will I need a fan? If a fan is needed, how much would this add to my electric bill? 
(Posted June 30th, 2009)

A: A good fan won't use a lot of electricity, but ventilating the basement will probably make your basement wetter. You see, when you put a fan in a basement window and set it to exhaust air out, you'll draw in air from other areas of the house or from the outdoors. If air from your living spaces is higher in humidity than your basement, its moisture content will condense on cooler surfaces, resulting in a wetter basement. The same phenomenon can occur if warm, moist, outdoor summer air enters a cool basement.

The way to keep airborne moisture out is to keep the basement as closed to the outside as possible. Seal basement vents and windows and even insulate windows if you don't need the daylight. Make sure that any basement doors to the outside fit well and have weather-tight seals (bulkhead doors are not airtight).

If, however, the moisture in your basement isn't coming from the air but from the ground, you have a bigger job on your hands. Speak to a contractor, who specializes in foundation building/rebuilding, about addressing the drainage outside of your foundation. Typically, this job entails re-grading the ground and installing rain gutters and proper foundation drainage. It's an expensive project, but one that will mean a dry basement, a longer-lasting house, and healthier indoor air.

- Li Ling for The Home Team