Moisture in the Basement

Moisture is just one of several reasons that basements are not recommended as a living space.

Basements usually are the wettest environments in the home with the highest possibility for mold to occur. Mold is an allergen to many people and has been know to cause death in a limited numbers of cases. If you decide to use the basement for anything but limited activities, make certain that you use building materials and furnishings with hard surfaces like tile. Softer materials like carpeting and carpet padding are particularly good at holding moisture that leads to mold and mildew. If you sheetrock the basement, make certain to hold both the sheetrock and wood framing off the concrete floor with at least a 1/2" piece of EPS insulation. This rigid insulation is commonly known as blue-board or pink-board.

The basement is often placed under a negative pressure from mechanical ventilation such as driers and venting from heaters and hot water heaters. This can lead to the active infiltration of soil and sewer gasses. Studies have shown how a negative pressure in the basement can even suck in the poison gas associated with both pesticides and termidicides placed in the yard up to 50 feet away from the house.

Removing Excess Humidity

Typically, excess moisture can be removed from the basement by three basic methods:

1. Heating the space (usually with space heaters)
2. Condensing the moisture (dehumidifiers)
3. Ventilating the space (fans)

Each method, as you would expect, has its pros and cons. Venting is the least expensive method of removing excess moisture from the basement but there are hidden issues.

Back-Drafting — a Possible Danger

Placement of the basement fan is critical, because air will always follow the path of least resistance. So the question is: when the fan turns on, where will the eplacement air come from. The answer is: from the closet, largest hole. If that hole(s) is near the fan then the fan will do very little for the humidity levels on the other side of the basement.

If the hole is the chimney, then may even have a dangerous problem. The bulk of older heaters draw "make-up" air from the basement. This is the air that goes up the chimney when the heater is running. If chimney draft is weak and the ventilation fan strong, the fan can pull the toxic flue gasses into the basement.

Hidden Costs of Ventilation

Basement air that you vent will most likely be air from the house that you have either heated or cooled. When you remove conditioned air, you increase your heating and cooling bills. The best solution for damp basements are:

1. Redirect or stop the water source outside the basement if possible
2. Capture and eliminate the water inside the basement (sumps, etc.)
3. Create moisture barriers where necessary (vapor barrier paints, masonry waterproofer)
4. Vent the basement from the floor level
5. Spot dehumidify as necessary with a high efficiency dehumidifier.

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