For Immediate Release (October 2, 2003)
Contact: Gordie Blum, (608) 231-9325
Email: gblum@fs.fed.us
Stop winter moisture build up from damaging your home
High levels of indoor humidity can cause long term problems
MADISON, Wis., October 2, 2003 -- The first killer frost of the year. You'd like to look outside to see if your flowers froze last night, but you can't because your windows are frosted up. If this is only a temporary battle and your windows clear up after a few days, consider yourself lucky. If they don't, then you might have an indoor moisture problem that could become expensive to fix if you don't take care of it.
"In northern climates, everyone will see their windows fog up some during the first cold snap. This happens because there is a lot of moisture stored inside the home," says Anton TenWolde, lead moisture researcher at the USDA Forest Service, Forest Products Laboratory (FPL). "But if the windows don't clear up after a few days, then you've either got faulty windows or your indoor humidity is too high."
TenWolde says the first thing you should do is check to see if you have a humidifier running or some other obvious moisture source. If not, then you need to better ventilate your home.
Research at the Forest Products Laboratory (FPL) has shown that short periods of moderate condensation in walls during cold winter periods do not necessarily lead to permanent damage. However, high levels of indoor humidity can result in moisture remaining well past the winter season, which can lead to serious moisture problems in walls and windows. Activities such as showering, cooking, and watering plants, coupled with a lack of adequate ventilation can cause excess humidity. Damp basements or crawl spaces or a leaky roof can also add moisture. This can lead to problems such as mold, wood decay caused by fungi and loosening of wood framing. Maintaining a reasonable level of indoor humidity (about 40% or less in northern climates) is the most effective method of moisture control.
"Normally, it doesn't take a great deal of ventilation to bring your humidity levels down," says TenWolde. "A small kitchen or bathroom fan left on constantly will usually do the trick." He adds that you should leave the fan on constantly until the humidity comes down, rather than run one intermittently. "A small fan running constantly will bring the humidity down faster than a much larger one that's only run periodically," he says.
TenWolde says another ventilation option that reduces heat loss is an air-to-air heat exchanger.
"Homes today have less natural ventilation than they used to. They are built tighter, and use energy efficient furnaces that don't run as often and take their combustion air directly from the outside. This makes them more energy efficient, but at the same time, it means higher indoor humidity. Air-to-air heat exchangers are a great way to solve this problem, but they are expensive."
He adds that simply having a chimney will usually provide enough natural ventilation. Dehumidifiers can also lower indoor humidity in regions with milder and more humid winters, but because they are generally designed to operate at higher temperatures and humidity levels, dehumidifiers are often not practical in cold winter climates.
The USDA Forest Service Forest Products Laboratory, located in Madison, Wis., was established in 1910 with the mission of conserving and extending America's wood resources. Today, FPL's research scientists explore ways to promote healthy forests and clean water, and improve papermaking and recycling processes. Through FPL's Advanced Housing Research Center, researchers also work to improve homebuilding technologies and materials.