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posted: 2/2/2013 1:00 AM

Home fix: Open crawlspace vents keep winter homes healthier

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By Dwight Barnett

Q. You have often said that crawl space vents need to be opened in the winter. Why is that? I always thought they should be closed to keep my water pipes from freezing.

A. I used to think the same thing, but the energy crisis of the 1970s led to a lot of research on how to maintain homes to conserve energy.

Over a period of time, it was discovered that making a home substantially airtight would also trap moisture and other gases inside the living environment. Warm moisture-laden air or humid air naturally travels from the warmer areas outside the home to cooler areas inside the home, where it can condensate back into water.

Inside the living areas of our homes, we control the flow of moisture using fans, air conditioners and dehumidifiers. Otherwise, a tightly sealed home could become a garden for mold spores.

We also need to control the levels of humidity in the crawl space, where water vapors can saturate the wood floor system, which then can lead to wood rot, mold growth, decay and structural damage.

Many of the crawlspaces I've inspected have elevated-humidity problems. To control the humidity, you open the crawl vents in the winter to allow the warm moist air to flow naturally to the cooler dryer outside environment.

In the summer, you close the vents to keep the warm moist air outside and away from the much cooler dryer air in the crawl space.

However, if you have a water line near one of the crawl space vents, that vent should be permanently sealed and insulated to prevent freeze damage to the water line.

In addition to preparing the crawl space for winter, you should also:

• Remove garden hoses from water faucets. A modern antifreeze faucet can be damaged if the hose is left in place all winter. If the faucet has an inside shut-off valve, close it until spring.

• Check to see if you have a kitchen or bathroom sink with plumbing on or next to an outside wall; the pipes could freeze. To protect the water pipes, leave the cabinet doors open or let the water trickle slowly during the night. Placing a 60-watt lamp on the floor just outside the cabinet doors also can provide enough additional heat to prevent freezing. Never place a light fixture inside the cabinet.

• Insulate the water lines in the crawl space or basement. Insulation conserves hot water while you are using it and prevents condensation from forming on the cold water pipes in the summer.

• Locate the main water shut-off valve and make sure it is operable. Most older valves are difficult to close and many will leak when you do turn them off. A minor repair now could save you from an expensive repair later if you are unable to turn the water off in an emergency.

• In mobile homes, electric heat tape may be necessary to prevent freezing of the exposed water pipes.

• Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at C. Dwight Barnett at

Scripps Howard News Service

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