Originally created 05/02/04

Q&A: Crawl space condensdation



Q. Stephen asks: I built my home four years ago in accordance with strict county and state energy requirements. My problem is condensation in the crawl space, along the foundation wall on the north side of the house during the winter months. The moisture is wetting my rim joist, floor joists, insulation and mud sill. I installed more foundation vents, but this hasn't helped. Do you have any suggestions?

A. The good news is that the energy-efficient techniques that were employed in the construction of your home have helped to create living space that is less drafty and more comfortable.

The bad is that whereas the home is less drafty, the crawl space is also less drafty permitting a buildup of moisture and condensation.

That you have an abundance of moisture and condensation is evidence that there is a lack of ventilation in the subarea or crawl space of your home. It sounds as if you already have employed step 1 of our recommendations - the installation of additional foundation vents at the perimeter of the home. If this doesn't work - and it sounds as if it hasn't - we suggest you install a layer of 6-mil (that's the thickness) polyethylene right on top of the ground in the crawl space.

Be sure to carefully cut around any interior piers, leaving enough excess material so you can tape a "collar" around these piers to minimize the transfer of air. All seams should be lapped a minimum of 6 inches and taped with an industrial-strength tape. Duct tape like that used by heating contractors will do. Most major hardware stores or home improvement centers will have just what you need.

If this doesn't solve the problem, consider contacting a heating and sheet-metal contractor and examine the possibility of an auxiliary fan in the crawl space, which, in combination with the other preventive steps, should do the trick.