Crawlspace Mold

Crawlspace Mold Inspection

Crawlspaces are notorious for mold growth. These areas are usually hard to access and evaluate since they tend to be very damp, cramped, and, like attics, are neither really inside nor outside. Many people are reluctant to check for crawlspace mold for fear of snakes and other varmints. Truth is, it’s the potential for mold growth here should be giving them the heebie-jeebies! The EPA claims that crawlspace mold can pass through cracks in walls and floors to infest the interior of a building.

Detection of crawlspace mold is a combination of basement and attic inspection procedures. Look for:

  • groundwater leaks.
  • wall leaks and dampness.
  • overhead leaking pipes.
  • the HVAC unit
  • a vapor barrier over the soil.
  • all framing members

Crawlspace Mold Abatement

If mold is present in these spaces, the materials that it’s growing on should be replaced or thoroughly cleaned to remove the mold spores. Dirt floors should be covered by a heavy-duty vapor-barrier material.

crawlspace mold on wooden joistsThere are several important issues about dealing with crawlspace mold. If macrofungi are present, it’s extremely important to replace as much of the severely decayed wood as is feasible; otherwise, should the relative humidity increase sufficiently or the wood get wet, any fungus that is living will spread to any newly installed, unprotected wood that is in contact with the decay.

For crawlspace mold, follow mold removal guidelines discussed on this site.

To minimize future growth of micro fungi, rather than spraying a crawlspace with bleach solution, after cleaning the framing should be sprayed with a borate mildewcide. This leaves a residue to protect the wood. After the mildewcide dries, a light coat of spray paint can be applied to the entire wood structure (joists, subflooring) to seal in any loose mold spores. When water-based materials are used, the crawl space must be allowed to dry out before being closed up. If the weather is dry, use an exhaust fan. If the weather is humid, use a dehumidifier. If solvent-based compounds are used, the crawl space should be ventilated at least until the odor is gone before being closed up.

Ventilation and Crawlspace Mold

Ironically, permanently increasing the ventilation may actually worsen a crawlspace mold problem by introducing more humid air. If you live in an area where the relative humidity is regularly or seasonally high, I recommend sealing a crawl space from the exterior and using dehumidification to keep the area dry (relative humidity at no more than 50 percent). Building codes in many regions mistakenly require crawlspace ventilation. Many homes with crawlspaces have mold problems, caused by the high relative humidity of the ventilated crawlspace itself.

Crawlspace floors

Dirt floors in crawl spaces  should always be covered. If you have a dirt floor, cover the soil with heavy-duty vapor-barrier plastic. Get rid of all debris before installing the plastic and place mildew-resistant planks on top of the plastic to allow access to mechanical equipment or pipes. You may see water droplets under the plastic, which is telling you that the vapor barrier is doing its job. You should never see water on top of the plastic, however, because that indicates a problem: either a plumbing or foundation leak, or condensation due to excess relative humidity that must still be controlled.  A concrete floor is preferable to a vapor retarder alone. Painting the concrete after curing (drying) acts as a further guard against crawlspace mold.