Is Crawlspace Mold Causing My Health Issues?

Dear Jim:  I have noticed recently what looks like mold in the crawlspace under my home. What is causing this and how can I get rid of it?  Is it possible that this could be causing health issues for me?  I have noticed lately that I have had a lot of allergies and breathing issues I did not have before, and they seem to be getting worse over time.

Mold is a common problem under Bay Area homes, and something I see frequently when I’m inspecting crawlspaces and basements.  I’m not a mold expert, but the 3 most common types we see are black mold (most toxic), yellow or orange mold (house eating mold (fortunately rare), and white mold. White mold is fairly common. Fortunately, it is the least toxic of the three, but can still present problems for those that are sensitive to it and can cause symptoms that develop over time if you have a chronic low-level exposure that you are unaware of. Mold spores can infiltrate through floors, ductwork, etc. and make their way into your living spaces from down below.

Black mold is more common in basement walls and bathrooms.

What causes this mold?  Primarily it is drainage issues that have not been addressed, with water infiltrating through and under old foundations and getting into the dirt areas, and occasionally into walls and floor structures.  Less frequently there are leaks in walls around poorly sealed windows and doors, siding or stucco, roofs etc., but it is mostly the subterranean moisture that is the culprit. You may also see a white substance on your foundations known as efflorescence. This is caused by water migrating through the concrete and depositing salts on the surface. Efflorescence is harmless, but it does indicate there are water issues that can lead to mold.

Efflorescence on Foundation Walls, (Not Mold)

So how can I solve my mold problem.? There are a few different approaches. Some companies will put in plastic in the crawlspace to encapsulate the soil, along with other measures to control the humidity.  From our perspective, this is not ideal as it doesn’t address the source of the problem and mold will continue to grow under the plastic.  Proper drainage is the best first-line defense, consisting of French Drains and downspout drainage along with appropriate ventilation, keeping the water away from your building and improving air circulation.  Over time these spaces will dry out and willnow longer be breeding grounds for mold. We have had clients report back that their health issues have improved significantly after appropriate drainage is installed, which makes us believe we are on the right track.

Crawlspace Mold Developing in Moist Soil (A Lack of Proper Drainage)


Conversations with Your Local Contractor is a feature by Jim Gardner of Jim Gardner Construction Inc. (with articles finessed by Lisa Gardner).  If you have residential, homeowner questions OR ideas for an article you’d like Jim to highlight, please send an email to

 Jim is a long-time Piedmont resident and has been doing structural repair and basement renovation in your neighborhood since 1983.  To schedule an estimate or for more information please go to our website at

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