Thick Polyethylene can Help Prevent Condensation in Crawl Spaces

By on May 20, 2014
crawl space vents

Question

I built my home four years ago in accordance with strict county and state energy requirements. My problem is condensation in the crawlspace, 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?

Stephen

Answer

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 news is that while the home is less drafty, the crawlspace is also less drafty permitting a build-up of moisture and condensation.The fact that you have an abundance of moisture and condensation is evidence that there is a lack of ventilation in the sub-area or crawlspace of your home. It sounds like you have already employed step one 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, then we suggest you install a layer of six-mil (that’s the thickness) polyethylene right on top of the ground in the crawlspace. You’ll want to 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 six inches and taped with an industrial-strength tape. Duct tape like that used by heating contractors will do just fine. Most major hardware stores or home improvement centers will have just what you need.

If this doesn’t solve the problem, then we suggest you consider contacting a heating and sheetmetal contractor and examine the possibility of an auxiliary fan in the crawl space, which, in combination with the other preventative steps, should do the trick.

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