Window condensation is a symptom of excess humidity within the home. When warm, moist air hits a cold surface such as a single-hung window or sliding glass door, it condenses and becomes a liquid. Fog and frost on windows and doors is also a form of condensation. Faulty windows do not cause condensation; windows are simply the first place that condensation forms because they have the coldest surface.
Recessed windows, such as bay and bow windows, usually collect more condensation than other window styles. Bays and bows tend to be a few degrees cooler due to air circulation being more restricted, and because they hang away from the insulated wall.
What Causes Window Condensation
Condensation can result from a number of factors that lead to excess moisture in the air. Modern construction techniques and products have resulted in homes that are tighter and much more energy-efficient. They also make it more difficult for warm, moist air to escape. New window designs are not as drafty as older windows, which creates another barrier to air exchange. Heating systems, plants and the use of humidifiers add more water vapor to the air. Daily activities such as cooking, showering and dishwashing also contribute a surprising amount of moisture to indoor air.
How to Cut Down on Condensation
Ideal humidity levels can vary from home to home, and generally range between 30-50%. To determine exactly how much humidity is in your home, you can purchase an inexpensive hygrometer at a hardware store. To reduce condensation issues, it is vital to lower the level of indoor humidity. High humidity levels can cause a number of damaging and costly problems, such as stains on walls and ceilings, rot in wood windows, mold and mildew growth, buckling floors and peeling paint.
To allow moist air to escape your home, increase ventilation with regular use of exhaust fans and by opening windows if weather permits. Be sure gas burners and clothes dryers are vented to the outside. Have a professional roofer inspect your attic to be sure there is adequate attic ventilation that allows moisture to escape.