Crawl Space Moisture
Crawl space moisture is minimally managed by ventilating with outside air. But why is this so important? Whether or not your goals are crawl space insulation or crawl space barriers- crawl space moisture barriers are more complicated than simple venting can address. Without adequate measures to control moisture in crawl spaces, there exists the danger for such things as bacteria and mold spoors being created. These things along with chemical vapors and radon can migrate into the home from damp crawl spaces.
Even building code authorities recognized that the previous codes did not address the issues properly. Unfortunately, even though recent changes in The Standard Building Code specifications have increased the required amounts for crawl space ventilation to one square foot of opening per one hundred fifty square feet of crawl space, the revision does little to address the situation sufficiently. Here is why:
- The majority of moisture in crawl spaces is not because of ground moisture. There is some, however, and it should be addressed. Rainwater must be directed away from the foundation with a gradient.
- Air flow left on its own to move in and out of a crawl space through foundation vents is minimal- inadequate to control crawl space moisture.
- The amount of moisture in a crawl space is dictated by outdoor atmospheric conditions.
- Regardless of whether or not the vents are opened or closed, the moisture in a crawl spaces fluctuate simultaneously with the water vapor content of the air outside of the home.
Simultaneous Fluctuations
Humidity inside a crawl space fluctuates in proportion to the outside atmosphere. It is not feasible that the moisture will instantaneously move down through the ground to travel to the footers where it is then delivered through a vapor barrier to move above the ground again.
Consider the Reverse
Consider also the reverse direction of water flow when it is raining. After a significant amount of rain falls the ground is saturated. The crawl space moisture however, declines immediately after the weather front moves on. Yet the dampness in the crawl space changes even during subtle changes in weather conditions because of vapor diffusion which occurs through open foundation vents as well through closed ones. This also is occurring through block wall foundations and through every opening in the deck framing of the home.
Certainly there needs be more action than simple foundation venting to address these issues. It is certain as well, considering the implications to one’s health, due to the moisture inside crawl spaces that is created, venting and moisture barriers must be put into place to address the moisture inside the crawl space.