In my last post I explained how wet crawl spaces pose problems to both the home and the homeowners. This post is about keeping crawl spaces dry.
My friend Bennie Marshall and I had an interesting conversation about wet crawl spaces the other day on the phone. Bennie is a crawl space specialist in South Carolina who solves crawl space moisture problems. He installs airtight ground-moisture barriers and sells his patented crawl space moisture barrier material to home performance contractors all over the country.

How the Problem of Wet Crawl Spaces Occurs

Bennie is taking a lot of calls from customers and distributors of his products about dripping wet floor joists. As most people know, wet wood rots and invites termites and carpenter ants so you don’t really want dripping wet floor joists. How do floor joists become dripping wet and why is this a particular problem this year?
The answer may have something to do with the hot summer and the continuous operation of air conditioners. The moisture problems were there in past years but the same problems are more severe and noticeable this year. The uninsulated floors are refrigerated by cold air collecting on the floor from the air conditioning. The crawl space collects moisture from the ground and from hot humid air outdoors that ventilates the crawl space. The refrigerated floor joists condense water out of the humid air and they become dripping wet.

Wet floor joists grow mold and rot.

Use a Good Moisture Barrier

The moisture barrier is only partially effective if it isn’t sealed at the perimeter and at seams. The more airtight the moisture barrier the less water vapor, humid air, and ground-polluted air  enters the crawl space.
Bennie is a dogged master of the technicalities of ground-moisture-barrier installation. Bennie’s system is to use a premium polyethylene sheeting as a skirt called the Crawl Curtain around the foundation perimeter starting about 10 inches off the ground. The premium plastic overlaps the ground by about 10 inches too and anchors the cheaper ground plastic available at most building stores. Bennie uses a strong tape to seal the plastic ground barrier to the premium plastic skirt. The most interesting feature of this system is the skirt and its bonding strip. Polyethylene doesn’t bond well to adhesives. Bennie’s skirt is a fabric that is impregnated with polyethylene. The polyethylene is removed from a strip at the top of the skirt to help the premium plastic adhere to the foundation wall.

An airtight ground moisture barrier prevents most crawl space moisture problems.

Other Ways to Help against Wet Crawl Spaces

A lot of our books, such as Residential Energy and Homeowner’s Handbook to Energy Efficiency and our field guides have chapters on preventing and solving moisture problems.  You can use them to help mitigate the problem.
Other steps you could take would be to limit the extensive use of your air conditioner.

• Open windows at night to let in the cooler night air, which will help keep your house cooler during the day without requiring the AC to constantly be running.
• Fans are also a good option for keeping cool.  Use them only in the room you are occupying, as fans keep a person cool, but they do not cool the air.  Do not leave the fans running when you are not in the room.
• Install shades or blinds over the windows of the house, cutting down on the solar heat gain.  This will help keep your home cooler and cut down on the need to run the Air Conditioner as long or as often.

 
Learn more about the Crawl Curtain at Bennie’s blog.