Excess moisture, introduced by way of unsealed, vented crawlspaces, contributes to wood rot, mold growth and increased pest activity. Moisture in crawlspaces often migrates to the upper levels of the home through a “stack effect.” In essence, whatever air is below the house is also in the house. As warm air rises and escapes through the upper levels of the home, new air finds its way into the home to replace what’s been lost. Intake air comes in at the lower levels – through unsealed crawlspaces. This may lead to costly problems such as cupping of hardwood floors, mold growth, increased air conditioner loads, and swelling of millwork/cabinetry. Air infiltration from the crawlspace often carries odors and may contribute to poor indoor air quality and uncomfortable humidity levels.
Excess moisture in crawlspaces has also been associated with contributing
to increased energy consumption. Wintertime ventilation cools the
crawlspace contributing to heat loss from the home. In the summer,
introducing warm outside air under the home contributes to heat gains,
increasing cooling loads. Ventilation of a crawlspace to control
relative humidity only works consistently in an arid climate. In
most climates, ventilation can actually add significant quantities
of moisture during humid times.
Why Vented Crawlspaces Can Make Humidity Worse
Venting a crawlspace will either add moisture to,
or remove moisture from, a crawlspace depending on the moisture
content of the ventilation air compared to the desired conditions
of the crawlspace. Venting with dry air reduces moisture levels
in the space, while venting with moist air contributes moisture.
It is false to assume that venting will automatically bring in
“good” air and push out the “bad” air. If the outside air is humid
and the crawlspace air is humid, you’re not making any improvements
by venting. Since venting either wets or dries the space depending
on outside conditions, there is no way to guarantee a specific
moisture level in a vented crawlspace.
A Better Solution.
The solution to this dilemma is to close the crawlspace.
One of the objectives of closing crawlspaces is
to reduce sources of moisture entering the space. Even when done
meticulously, closing a crawlspace will significantly reduce the
moisture but not eliminate it. Active conditioning of the space may
be necessary to maintain proper humidity levels. A dehumidifier can
provide long-term, active moisture control and ensure humidity levels
are maintained at a specific level which is adjustable by the home’s
occupant.
It is important to note the areas of concern when
taking steps to responsibly convert your vented
crawlspace to a sealed and conditioned space. Those
include, but are not limited to: assuring proper water drainage,
installing vapor barriers, consideration for combustion and carbon
monoxide and sealing outside vents and controlling moisture with
a crawlspace dehumidifier.
