Because windows are usually the coolest surfaces in a house, they may collect condensation in winter, when outdoor temperatures are low and indoor air is warm and humid. These conditions encourage mold and mildew and can cause window frames and sills to rot.

To reduce condensation, increase ventilation—just using bathroom fans and kitchen fans can make a big difference. Running the air conditioner also reduces humidity. Also keep showers short and run only full loads in washers and dishwashers.

f doing these things doesn’t help, contact an insulation contractor. Also see the HomeTIps Dehumidifiers Buying Guide.