Fight the humidity under your feet

There are thousands of houses in Georgia and throughout the Southeastern states that are constructed over crawl spaces. Traditionally these crawl spaces have vents installed in the foundation walls. Until recently, the vents were required by building codes.

In the last 15 to 20 years, however, our understanding of crawl spaces and venting has taken an about-face.

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AquaGuard

Basement encapsulation is one way to keep a crawl space dry – and better than the traditional vents.

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In the early years of the last century, houses were often constructed on piers, and the spaces under the houses were left open. Moisture that naturally evaporated from the soil simply dissipated into the atmosphere.

Later, builders began to enclose crawl spaces. Their theory, and it was somewhat true, was that an enclosed crawl space would save on heating and cooling bills by reducing the temperature difference between the house and the crawl space.

For that same reason, many previously open under-floor spaces were enclosed. But to allow the moisture to continue to escape instead of building up in crawl spaces, vents were installed in the homes’ foundations.

The misunderstanding here is that moist air does not necessarily escape from the crawl space through the vents. In fact, sometimes humid air from outside comes into the crawl space through the vents, especially in the hot, humid summer months.

Humid exterior air moving into the crawl space, combining with evaporated moisture from the soil, results in elevated levels of humidity. That provides a perfect climate for mold growth in the crawl space.

Interestingly, the latest research shows that enclosing the crawl space is better than venting for reducing the humidity levels.

If your house is constructed over a crawl space, it is natural for you to wonder what to do about the problem of elevated humidity. Crawl spaces can be sealed. In my research, I have found numerous strategies for enclosing or sealing them.

These strategies vary in complexity and practicality. There are, however, several procedures that are consistent across all of the strategies and can, for the most part, be done by a typical homeowner with a little time and tenacity. Here is a short list.

Keep in mind that this list stops short of a complete job, but makes the attempt to address the big issues.

1. Eliminate any water entry into the crawl space. This may require cleaning out or installing gutters and downspouts and/or regrading the soil around the house to slope away from the house. A slope of 6 inches in the first 10 feet away from the house is desirable. If water continues to enter the crawl space after gutters are installed and the soil is regraded, you will need to contact a professional water-proofing contractor to devise a strategy for eliminating the water entry. This first step is extremely important. None of the other procedures will work if water is getting into the crawl space.

2. Install a 6 mil polyethylene vapor barrier over the crawl space dirt. If possible, you should run the vapor barrier up the foundation walls and piers and secure it with construction adhesive or pressure treated wood nailing strips. Do not go all the way to the top of the foundation wall. You should leave at least a 3-inch space of exposed foundation at the top of the vapor barrier for termite inspection.

3. Using 2-inch thick rigid Styrofoam pieces, seal off the crawl space vents. The foam should fit as tightly as possible into the interior of the foundation vents.

4. As much as possible, weather-strip the crawl space door.

5. If you have a gas burning appliance in the crawl space, like a furnace or water heater, you will need to consult with a licensed heating and cooling contractor to make sure that you are not cutting off more oxygen than the appliance needs for combustion.

6. Make sure that all heating and cooling ductwork in the crawl space is well sealed and free from leaks. Discharging cooled air into the crawl space will lower the crawl space temperature and increase the relative humidity.

7. Make sure that all vents from bathrooms, kitchens, and clothes dryers are well sealed and discharge to the exterior of the house.

For more strategies for sealing your crawl space, I recommend contacting Advanced Energy at www.advancedenergy.org or call 1-800-869-8001.