Crawl Space Mold Remediation

What to do when water damage to crawl space creates a big mold problem.

by Thad Godish, Ph.D

We have a crawlspace problem. We noticed that the insulation and wood is wet. The plumber detected no leaks and said it was due to condensation. We had two different mold removers tell to us two different remedies: (1) a house and crawlspace dehumidifier (Humidex) and (2) a new drainage system for removing moisture under the existing plastic vapor barrier.  It seems they disagree about the source of the wetness (ventilation vs. drainage). We did not have any problems for 7 years in this home. I am confused as to how they seem to diagnose the problem and how do we trust that they know the source from just looking at the crawlspace ( which makes a big difference in the treatment once the mold is removed).  We think that the excessive moisture is due to a leak in our dryer hose as a mouse chewed a hole in it under the house last year. In repairing it perhaps we did not connect it tightly enough.

INFO LINKS Dehumidifiers Overview - view all Dehumidifiers sold by AllergyBuyersClub.com Dehumidifiers Comparison Chart - a comparison with pluses and minuses of all the best dehumidifiers Mold Solution Guide - a quick buyers guide of the best recommended products to solve mold allergy problems Mold Learning Center - FAQs and Mold Prevention and Cleaning articles

The mold contractors do not agree. We want to remove the mold and prevent it from returning. The contractors seem to be interested in selling their remedy systems and dismiss our theory. Our concern: once we treat the mold, how dry does it need to be once the mold in the crawlspace has been removed/treated?  If the dryer hose was the problem, and that is cured, do we need to make the crawlspace drier than it was before the mold occurred - or is it more mold -sensitive, that is, once mold has grown requiring even dryer conditions than before.

- Dawn, New Jersey.

If your theory is correct then there should be a very localized pattern of condensation and mold growth in the area of the dryer vent hose leak.  The condensation should also come and go as you use the dryer.  The problem could then be easily resolved without major expense and competing remediation theories.

Based on your description, however, I think the two remediators don't think that the damaged dryer vent could cause such extensive condensation and mold-related problems in your crawlspace.  The fact that you didn't have a problem for seven years may or may not be significant.  Many homeowners rarely go into their crawlspace and as such have little or no knowledge of its condition.  Seven years could easily pass without a homeowner having a sense that he/she had a moisture problem in the crawlspace.

If one does have a moisture problem in a crawlspace, it will typically require some combination of improved drainage and ventilation to resolve. Remediation will also require the treatment of the crawlspace timbers with a polyborate-containing paint to both inhibit mold growth and to "lock" mold spores in.

Mold requires high humidity of liquid water to grow.  Scientific studies indicate that little or no mold growth occurs below relative humidities of 75%.  As such, your goal should be to maintain humidities below 75% with values not to exceed 70% as your target.

Each individual remediator has some sense of the need to reduce humidity levels.  They are suggesting different approaches.  Each has some potential to work by itself but it is likely that a combination of drainage and ventilation will be needed.  If your house is near a coastal area, the crawlspace problem may be even more complicated.  In coastal areas, high crawlspace humidity may actually occur as a consequence of outdoor air moving into your crawlspace and then condensing.  In such circumstances, one may not have a drainage problem and ventilation is a major part of the problem.  In such cases closing crawlspace vents is recommended. 

First Published: Late-August, 2004
Updated: February 2007

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