October, 2004
CRAWLSPACES AND MOLD
Are
crawl spaces always a problem with respect to mold?
Mold can always be recovered from crawlspaces. Many are dirt-floored, and
the soil is filled with fungi and bacteria. The pleasant odor associated
with freshly turned soil is the result of volatile organic compounds
released from these normal soil components. These odors could penetrate into
the occupied space, but cannot be considered a significant health threat. As
long as the soil and the crawl space surfaces remain dry, however, mold
contamination should not be a problem.
Are crawl space molds
different from those that grow on surfaces in occupied spaces?
The usual damp surface molds (species of penicillium and aspergillus, among
others) can be common on crawl space surfaces. In addition, persistently wet
crawl spaces can support the growth of wood rotting fungi that not only
destroy the wood, but may produce fruiting bodies that release billions of
potentially allergenic spores.
Under what conditions do crawl spaces become "moldy"?
Any time water enters a crawl space, mold can become a problem. Some
crawl spaces are penetrated by ground water. The soil then becomes wet
enough to allow amplification of some of the molds, leading to production of
volatile organic compounds that cause unusual odors. Wet soil can also lead
to condensation on other surfaces within the crawl space. Another source for
water that can cause condensation is outdoor ventilation air. In the summer
the crawl space is generally cooler than the outdoors. When humid outdoor
air enters a crawl space, condensation is almost inevitable.
If the mold is only in the crawl space, why do we have to worry about it?
Other than the potential for wood rotting, you may not need to worry
about the mold if the ventilation patterns in the house are such that air
consistently moves from the house into the crawl space. If this is not the
case, then odors and spores will penetrate the occupied space whenever air
from the crawl space enters the home.
Does ventilation of the crawl space help prevent mold?
If the ventilation air is dryer than the air in the crawl
space (i.e., if entering the crawl space is not going to cause the water in
the ventilation air to condense on surfaces) then ventilation can be
effective. Thus in desert environments, ventilation can be a useful method
to keep a crawl space warm and dry. However, in hot humid climates,
ventilation of a crawl space with untreated outdoor air is likely to make
the problem worse.
Can crawl spaces be built (or remediated) so that they do not become
"moldy"?
The key to preventing mold in crawl spaces is to make absolutely sure
that no water will enter that can either lead to wetting of the soil or to
condensation on surfaces. If this is not possible, then crawl spaces should
be avoided. For existing crawl spaces, sometimes changing ventilation
patterns can help remove water. If all the water is coming from the soil,
the crawl space can be sealed so that no soil is exposed within the space.
This should prevent condensation on surfaces, but mold will still grow
beneath the sealant. If the sealant is not impermeable to volatiles, odors
may remain a problem.
Information based on the
writings of Harriet Burge Ph.D. posted in the Environmental Reporter.
Click here to learn more about Mold on the
U.S. Inspect Web site.
Contributed by David Kreider
Senior Network Manager
U.S. Inspect, LLC
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