Negative Effects of a Vented, Dirt Crawlspace

Tuesday, July 23rd, 2013

Due to the “stack effect,” the rising of warm air in a home, negative pressure in the crawlspace results in gases and moisture being “pulled” out of the ground. Since this can introduce unhealthy elements (radon) and mold growth supporting moisture to the space, it would seem logical that a dirt floor would be undesirable.

Mold and fungi need three elements to thrive: organic material, a common temperature, and moisture. Floor systems are wood  (organic), temperatures in a crawlspace average 60 degrees, and moisture is available from the dirt floors and any openings in the foundation. The easiest element to control is the moisture. By maintaining relative humidity below 65%, virtually no mold nor fungi can germinate or grow. Dust mites, whose droppings are the number one allergen in homes today, need moisture levels above 50% to thrive. So, it should be obvious that homeowners would want to transform their dirt crawlspace into dry, clean, conditioned spaces. What can be done?

Some homeowners feel pouring a concrete floor would solve the issues; however concrete shrinks when it cures so the joint at the wall may end up with tiny fissures and cracks. Additionally, concrete is not impervious to moisture transfer (wicking). And it does nothing at the walls which can be a source of moisture and gas intrusion. Plus, installing it can be extremely expensive.

For years, building officials, contractors and disinterested homeowners assumed the required installations of 6 mil plastic (vapor barrier) was adequate to control the moisture emanating from the ground. Our experience over the last 10 years of inspecting hundreds of dirt floor, vented crawlspaces proved conclusively that 6 mil plastic and foundation vents are not the answer. Due to the fact that such thinking has caused countless floor repair work, mold remediation and suspected rise in human health problems, it is a huge relief that building code officials have accepted and sanctioned the concept of sealed, conditioned crawlspaces.

While the building code still permits vented, dirt crawlspaces, in areas of the country where high humidity is present in summer, why would a homeowner still want such a crawlspace? So, if you own a home with a vented, dirt crawlspace you owe it to your energy budget and your health to seal and condition your crawlspace. Additionally, a crawlspace encapsulation will increase the value of your home tremendously.