Moisture Control
The hot and humid summer months of the deep south take a toll on your home, not only your family! David Horne shares his wisdom on the art and science of moisture control.
Moisture in a home is not uncommon. In fact, it is normal for the moisture content of wood in a crawl space to be 15% to 18%. When the moisture range exceeds this and begins to evaporate up into the home, noticeable problems may occur such as buckling of hardwood floors.
Lines of Defense
- Foundation Vents: help to move moist air out
- Vapor Barrier: plastic barrier that keeps moisture in the soil
- Ventilator Fans: forcibly ventilate the crawl space
Why would you need this third option? Forcibly ventilating a crawl space works for two reasons:
- The primary reason is that moving air can hold more moisture than stagnant air and moving air will carry moisture away.
- Warm air also holds more moisture than cooler air. This phenomenon is associated with the term relative humidity. If the outside temperature is 100% and the humidity is 95% – then the air is almost saturated. When the temperature drops, the air molecules cannot hold the moisture and condensation appears. This is where the morning dew comes from after a cool night. Crawl spaces are cooler than the outside temperature. By warming the crawl space you increase the airs natural ability to hold the moisture and thereby remove condensation.
The difficulty comes into play with extremely hot months. Today’s air conditioners blow colder air than those of old, and people keep their thermostats set at lower temperature than they did 20 or 30 years ago. As a result, crawl spaces are cooler and thus more susceptible to condensation buildup. Because of this condensation build up, we occasionally need to install dehumidifiers or encapsulate the crawl space. As a result of the condensation buildup, it is not unusual for wood moisture contents to spike a little in the summer.
it is very rare for crawl space moisture to affect interior moisture. Wood moisture content in a home is usually lower than that under a home. Generally if there are issues with excess moisture in a home’s interior one should look at the air conditioning system and the attic ventilation. There are a great many homes that need improved attic ventilation. This is especially true with older homes that have had insulation added, primarily because the insulation company covers the soffit vents with blown insulation.
