The
Ventilation Controversy
You will probably hear from many sources that ventilation is
important to remove humidity from crawl spaces. However,
studies from a Building Science perspective show that crawl
space ventilation actually adds humidity and offers pathways for
the introduction of mold spores. The old school of thought
assumes that air enters one CS vent and exits another taking
humidity with it. The actual dynamics in the typical CS
show that air, outdoor pollutions and humidity enter
all
the vents simultaneously because of the "STACK
EFFECT." The "STACK EFFECT" occurs in
all buildings where air will exfiltrate from the upper areas of
the home, which forces infiltrations into the lower areas.
This effectually turns your crawlspace into a giant vacuum
cleaner drawing in wet and dirty outside air and then this
contaminated air is sucked up through the living space via
by-pass pathways. RK
Mold/Mildew
You
should view the mildew as a symptom... if there is mildew
growth, there is also the chance of moisture damage occurring in
the wood framing. Taking the appropriate steps will not only
minimize or eliminate the odor but also preserve the value of
your home.
Moisture
must be reduced to effectively control mildew in a crawlspace.
To
that end you must be absolutely certain there is no surface
water entering the crawlspace. Look into the crawlspace after a
heavy rainstorm for evidence of water. If you find any surface
water at all, the following steps will be futile. You must
eliminate it first. Check the gutters and leaders for breaks and
blockages. Check the drainage around the house, and make repairs
as necessary. Repair cracks in foundation walls and if
necessary coat with a below-grade cement-based waterproofing
paint.
Lessen
the overall amount of water vapor entering the crawlspace from
the ground...
This
is accomplished by laying a heavy plastic tarp... 5 mil or
thicker...over the entire floor. If multiple sheets are
used, they should be folded together at the seams and/or at
least overlapped at least 3 feet. Use stones to hold the
plastic down. This plastic acts as a vapor barrier and
will eliminate much of the movement of water vapor from the
ground into the crawlspace, with the added benefit of lessening
radon infiltration
Automatic
Crawlspace Venting
It's
important that a crawlspace be as dry as possible.
Wood-destroying fungi thrive in dark and damp conditions, as do
subterranean damp-wood termites, and musty crawlspace odors can
rise into living areas. Most crawlspaces have vents that are
supposed to help reduce humidity, but in fact are moisture
entrances and in many cases bring the mold spores into the crawl
space. The crawl space should be sealed including all vent
openings and any other infiltration entrances. Sealing the
infiltration entrances and using an exhaust fan will cause the
crawl space to go slightly negative. see
ref. Ventilation
Controversy above.
A
sophisticated way to accomplish this in a crawlspace is with the
PREVENTILATOR. The system consists of a fan, a dial-operated
HUMITRAK control in the living area and an adjustable remote
sensor in the crawlspace. The beauty of it is that you don't
have to enter a crawlspace to adjust the sensor's humidity
level. You dial the HUMITRAK to the desired setting, and the
remote sensor turns on the fan when the humidity level is
reached. A light on the HUMITRAK tells you the fan is running.
The
manufacturer calls its fan the PREVENTILATOR. It has a
motorized and insulated cover made weather tight with a rubber
gasket. The PREVENTILATOR is sold directly from the manufacturer
and costs about $249 plus shipping. Contact Tamarack
Technologies Inc., 11 Patterson's Brook Rd., P.O. Box 490, West
Wareham, MA 02576; 800-222-5932. www.tamtech.com/newpage12.htm
