Weeping windows in the winter can create problems for homeowners. Why is window condensation a problem and what can be done about it?
Water — whether it leaks out on the floor around a shower or drips down the inside of a window — invites mold and mildew damage to a home. In the worst cases, the moisture wicks into the adjoining wall timbers and generates structural damage called dry rot.
For centuries, builders have battled to keep water and cold air outside and dry air and heat inside. Homeowners face the challenge now, more than ever, because a modern home is built to be energy-efficient or “tighter.” Tighter homes actually retain more moisture. That means moist air ends up inside rather than leaking out.
During the heating season in Western Washington, where humidity levels in the air often exceed 40 percent, moisture that hangs in the air can condense, turning vapor into water dripping down window panes. Sometimes a rolled-up towel is the only way to catch all the water before it runs off the sill.
Windows can have different kinds of condensation problems. Moisture on the inside of a storm window indicates that the prime window is allowing air and moisture to leak to the storm window where it condenses. If moisture condenses on the inside of a window pane, airborne water is trapped in the house due to poor air circulation and exchange. Bad seals in double-pane windows also can allow moisture to build up between the panes of glass. Temperature changes cause condensation or a “milky” appearance between the panes.
Weeping window solutions
The simple solution to water condensation or weeping windows, said Rick Cantonwine, an energy counselor with Clark Public Utilities, is to raise the glass temperature above the dew point — at which condensation occurs — and at the same time to lower the amount of moisture in the air.
“The glass temperature can be raised by letting warm air touch the window or by replacing the window with one that has less heat loss,” Cantonwine said. “Or cover the window with some kind of plastic to keep the room air (and moisture) away from it.”
Other tips from the experts:
• Use exhaust fans in your kitchen, laundry area and bathrooms to pull moisture-laden air out of the house.
• Vent gas burners, stove exhaust and clothes dryers to the outdoors.
• Shut off furnace humidifiers and other humidifying devices in your home.
• Be sure that the ventilating louvers in your attic, basement and crawl spaces are open and amply sized.
• Open fireplace dampers to allow an escape route for moisture-laden air.
• Air out your house a few minutes each day.
• In the worst cases, where moisture is contributing to mold and mildew or possibly an allergy condition of an occupant, a dehumidifier may be a good investment.
Some experts recommend connecting a small duct from the outdoors to the return side of a forced-air heating system, so that fresh air is drawn into the house. A damper on the system allows the homeowner to control the amount of incoming outside air.
Better attic ventilation may also be needed to keep condensation from dripping from the inside of the cold roof onto ceiling plaster, paint and insulation.
Condensation science
Condensation occurs when the physical state of matter changes from a gaseous phase into liquid, and is the reverse of evaporation. It’s all about water molecules in the air getting colder and slowing down, just like rain.
Older homes with single-pane windows often have the bigger problems. Replacing these windows with double-pane vinyl upgrades is sometimes worth the investment in comfort and in resale value because of the energy efficiency they offer, contractors say.
There are numerous home improvement retail stores as well as websites offering information and advice about how to handle window condensation problems.
Some sites:
• http://www.clarkpublicutilities.com, search energy adviser columns.
• http://www.finehomebuilding.com.
• http://www.northwestenergysavers.com.
• http://www.renewalbyandersenwindowsnw.com.
• http://www.milgard.com, click on energy-efficient windows.
• http://www.glassdoctor.com.
A historical note: The term “dry rot” comes from an 18th century term used in England to describe decay in dry wood caused by fungus. Paradoxically, in order for the fungus to get started and remain active, timber must have a moisture content of about 20 percent. Drying out the wood will kill the fungus, but left untreated, dry rot destroys wood.
The Energy Adviser is written by Clark Public Utilities energy counselors, who provide conservation and energy use information to utility customers. Send questions to energyadviser@clarkpud.com or to Energy Adviser, in care of Clark Public Utilities, P.O. Box 8900, Vancouver, WA, 98668. Past topics are available at http://www.clarkpublicutilities.com.
