Dampness and Humidity Problem Solver

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Severe Humidity

I have a severe humidity problem in my house, which is two years old. The indoor relative humidity levels run 70 to 80 percent during the winter months. My double-glazed windows are constantly covered with moisture and the varnish is beginning to peel. The attic is vented by six roof vents and six eave vents. The walls contain 6 inches of Fiberglas insulation with plastic vapor barrier and there’s 12 inches of cellulose insulation in the attic. To take care of moisture in the bathroom, I have a power vent to the out side. The range hood is not vented but there is only minimal cooking done on the range.

It sounds as if you have a tight, energy-efficient house. While this helps keep your heating costs in line, it inhibits fresh-air infiltration that would otherwise help to control humidity. Condensation problems often appear in the fall after the house has been exposed to the warmer moist air of the summer months. Every thing in the house including wood framing, walls, floors, clothes, furniture and so on absorbs the moisture from summer air.

When the drier, cooler weather arrives, the house tends to dry out and thereby increases the relative humidity of the interior air. If the temperature at the windows is below the dew point, this moisture will condense.

If this is the cause for the moisture buildup in your house, it can be corrected by ventilating the rooms. Open the windows in each room for about an hour during the warmest part of the day. The dry outside air can then mix with moisture-laden household air and reduce the overall humidity.

There are other possible causes for moisture buildup in your house. If your basement takes on water after a rain, make sure it’s pumped out as soon as possible. The water vapor will migrate up to the habitable portions of the house. Try to avoid storing firewood in your basement. As the wood dries, the moisture it loses will con tribute to the relative humidity of the household air. Also, if there is a dirt floor in the crawlspace it should be covered with 4- to 6-mill polyethylene sheets even if the soil feels dry. According to the Small Homes Council at the University of Illinois, a 1000-square-foot house can release as much as 18 gallons of water per day through evaporation in the crawl space.

Another possible source for excessive moisture buildup in the house is a clogged heating-system chimney. One of the products of combustion in a gas-fired heating system is water vapor. If the chimney is clogged, the water vapor will pour into the house. This must be checked not only because of the moisture- level buildup, but because poisonous carbon monoxide could be leaking into the house as well.

Sweaty Windows

The windows in my house sweat and produce excessive moisture. Water accumulates on the window sill and literally needs to be dried up with a sponge or rag. This occurs daily in the wintertime. The house is three years old, and water damage to the drywall is already visible. Any suggestions to eliminate the moisture buildup would be appreciated.

The condition is obviously the condensation of excessive moisture present in your house. Although I can’t deter mine the exact cause of the problem, I can recommend three possible sources for excessive moisture.

Many homes with warm-air heat have a humidifier mounted on the furnace. If you have one, the unit may be malfunctioning, introducing too much moisture into the airstream.

Another moisture source is a bathroom exhaust fan that vents into the attic, and not outside. The fan may also be blocked, or its outlet in the attic floor may be covered by insulation. The fan should exhaust moisture into a duct that leads to a roof vent or through a sidewall with a rainhood for protection.

A third source is a dirt crawlspace under the house. Moisture from the soil is pulled into the crawlspace, then into the house. In this case, install a vapor barrier of plastic sheeting above the dirt floor and ventilate the crawlspace. There should be at least two vents, with a total free area of ‘A of the crawlspace area.

Condo Humidity

I need advice on how to deal with a humidity problem. I close my condominium apartment for a few weeks at a time. When I return, I find a bad case of mold and mildew I’m considering getting an electric dehumidifier to solve the problem. Is there a better solution?

Whether or not a single dehumidifier will be adequate for your purpose depends on the configuration of your apartment.

If you have a number of rooms, you’ll probably need more than one dehumidifier because the partitions will interrupt air circulation between the rooms. You can substitute a fan for one of the dehumidifiers if it’s positioned so that air is moved from a moisture-laden room to one with a dehumidifier.

Dehumidifiers are usually equipped with an over flow control that shuts the unit off when the reservoir is filled. To make sure that the units keep working, run a hose from each one to a sink or toilet.

If your condominium apartment is centrally air conditioned, then a good cost-effective solution is to install a humidistat in parallel with the air conditioner thermostat. With this system, whenever the humidity builds up beyond a preset limit, the air conditioner will be activated even if the temperature in the apartment is not high. This will remove excess moisture from the air throughout the apartment.

Condensation in Sunroom

During cold weather, condensation forms on the windows in my unheated sunroom adjacent to the living room. A pair of French doors provides access to the sunroom which, incidentally, was built over a concrete slab. The condensation is so heavy that it forms mildew on the walls. A dehumidifier has proven itself ineffective. How can this be corrected?

Although the sunroom is closed off from the living room, it’s likely that water vapor is migrating from the living room into the sunroom. Moisture will travel from a room with high vapor pressure to one with lower pressure. In most cases, vapor pressure is higher in a warm room than in a cool room. Check the wall around the French doors and seal any openings you happen to find. Seal the perimeter of the doors with weatherstripping. You can also tape a large polyethylene sheet over the doors and their molding to see if this decreases the condensation. The plastic needs to be taped over the doors on the warm side of the room (the living-room side).

If the problem persists, I would suspect that water vapor is entering the room through the concrete floor slab. When the room was built, a plastic-sheet vapor barrier should have been installed under the slab. You can determine if moisture vapor is migrating through the slab using a simple test. Place an 8-inch square of aluminum foil on the floor, and tape down its perimeter. If, after a day or two, the underside of the foil is damp, you’ve located the source of the problem. In this case, you can use an electric heater and warm the sunroom to reduce or eliminate the condensation. Heat helps the moisture vapor remain suspended in the air, and it warms cold surfaces, which further decreases the chance of condensation.

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Updated: Wednesday, August 10, 2011 5:40