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
