Crawl Space Moisture and Mold Control

One of the top three areas where mold can be found in a dwelling is a crawl space.  For the most part, mold in a crawl space is a direct result of outdated building codes.   The historic common building practice was to insulate the floor above the crawl space and to leave the crawl space’s wall vents open, for ventilation.   The idea of installing vents was the belief that any moisture buildup in a crawlspace would vent to the outside, a seriously flawed design.   Instead of expelling moisture (at least in areas with humid summers), the open vents allow moist air into the space that would mix with the cool surfaces of the crawl space, allowing condensation. The mixture of hot and cold are allows moisture to drop out of the air.   The proof of this is drooping insulation in a crawl space and mold on the exposed wood ceiling.

The vented design of a crawl space allows the space to draw humid air into a cold crawlspace in summer. A  crawl space will, by nature, be cool in summer and less humid than outdoor air, so moisture and humidity will be drawn to the space allowing the humid air to condense on the cold surfaces of wood and concrete in the crawlspace. This provides a continuous source of moisture in the crawl space.

Example of a remediated, vented crawl space. 

On a basic level, humidity is a real driver of mold growth in a crawlspace, but you can also have other sources. Physical water intrusion, gutters, plumbing leaks as well as improper exterior management can be contributing factors to creating an ecosystem conducive to mold growth

The historic design of a crawl space creates a perfect environment for mold. It has oxygen, it is dark, there is ample food (dirt, wood, insulation, animal waste), and as discussed the temperature humidity level creates the perfect ecosystem for mold growth.

Remediation of a crawl space will have the benefit of removing existing mold and future proofing the space with the application of a fungistatic coating on the wood in the space, which is the food source for the mold

Some more modern crawl spaces or crawl spaces that have been upgraded, can include conditioning of the space. Basically, sealing the space, insulating the walls and heating and cooling the space. Typical conditioned crawlspace improvements can average $5,000.00 plus or minus depending on specific site conditions. Not a huge fan of conditioned crawl spaces since you are heating and cooling an area that is not habitable. Also no one is going to compliment you on the crawlspace.

Alternate approaches to conditioned spaces is moisture management, which can take many forms both within and outside the footprint of the area including outside wall insulation.

Crawlspaces can be affordably sealed to manage humidity levels including proper operation of a dehumidifier to keep humidity down. Dehumidification should operate continuously with a drain hose, so manual emptying is not necessary