by Dwight Barnett
Scripps Howard News Service
Q: I live in a five-room ranch-style house with hot water baseboard heat. The attic has 6 to 12 inches of insulation and a small vent at each end. We had a one-ton air conditioner installed two years ago. The one-piece air handler is in the attic. The emergency overflow pan is attached to the bottom of the unit, with an overflow pipe exiting next to the back door. The regular condensation pan is above this pan, with its drain exiting farther away.
The first low temperature of the winter last year we had a wet ceiling under the air handler. The attic unit was sweating and running everywhere. The installer caulked openings where the intake air hose flange attached to the air handler. He also put insulation around the sheet metal collars leading to the five rooms.
The rest of the winter we had no problem. Then at the end of this December, we noticed water coming out of the emergency overflow onto the deck. I would appreciate your thoughts on this problem. --T.S., Randolph, Mass.
A: First off, you do not have enough insulation in the attic. Contact your local building authority to find out exactly what insulation R-value is needed in your area. The R-value (resistance to thermal transfer) of insulation will vary with the type of insulation you have.
A rule of thumb you can use is as follows: For loose fill fiberglass, R is equal to about 2.2 per inch. For fiberglass batts, R is equal to about 3.1 per inch. For loose fill cellulose, R is equal to about 5 per inch.
Second, you need a vapor barrier between the living areas of the home and the attic. The vapor barrier stops the flow of moist air from one area to another. You can purchase insulation that has a built-in vapor barrier; however, the vapor barrier has to be next to the heated side of the ceiling. Do not place a vapor barrier over the existing insulation.
There are paints available that have some resistance to moisture migration. Once the vapor barrier is in place, the moisture that used to go through the ceiling will be trapped inside the home.
Third, it appears that your home is generating a lot of excess moisture. Have a qualified heating contractor check the boiler for leaks and for proper venting of flue gases. Then check the basement or crawl space for signs of water penetration. The dirt floor of a crawl space should be covered with a vapor barrier.
Make sure that bathroom and kitchen vent fans are in a good working condition and that they vent to the exterior of the home. If you have a clothes dryer, it too has to vent to the exterior of the home. A modern clothes dryer can produce several gallons of moisture for each load of clothes.
Fourth, if the moisture in the attic persists, have a powered vent fan installed in one of the gable end vents. The fan should be controlled by a humidistat so that it works mainly in the winter. In warmer climates, a thermostat is also used in conjunction with the humidistat so that the fan cools the attic in the summer.
And, finally, you did the right thing in insulating and sealing the attic unit and the grills attached to the unit. When adding vapor barriers to control the flow of moisture, remember this: moisture (warm air) always travels from hot to cold (where it condenses) and from more to less, so start at the foundation and work your way up through the home to locate and seal out moisture.
(C. Dwight Barnett is a master inspector certified by the American Society of Home Inspectors. Questions may be addressed to him at P.O. Box 14091, Evansville, IN 47728, or e-mail dbarnett@evansville.net.)
Resources American Society of Home Inspectors (ASHI)
To locate an American Society of Home Inspectors inspector near you, call or visit the website of ASHI.
American Society of Home Inspectors
Website:
www.ashi.org
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