Messages and Online Forum Q&A

Re: Creating a vapor barrier

From: info@builderswebsource.com
Category: Drainage/Waterproofing
Remote Name: 63.198.181.43
Date: 15 Dec 2002
Time: 12:06 PM

Comments

Due to a high water table, water nearly reaches the bottom of your floor joists in your crawl space. To mitigate your moisture problem, follow these steps:

First, download and read our technote to familiarize yourself with PRINCIPLES OF RESIDENTIAL DRAINAGE AND BASEMENT WATERPROOFING.

Next, as you have a clearly severe situation, we suspect that you may have more than just a high water table. You may also have surface drainage issues (include runoff from the roof or downspouts), which are compounding your problem. We urge you to consult with a civil engineering company who can survey your property and identify all the sources of water. While installing a perimeter French drain may be part of the remedy, you may also need a separate drainage system to divert runoff from rain, sprinklers, and other runoff.

Furthermore, with standing water in your crawlspace, you may already have signs of water damage, such as dry rot, mold or other wood-damaging conditions. Laying a vapor barrier over the raw ground under your home is generally a good practice, but only once you've identified and rectified the sources of the water intrusion in the first place. As you suggest, installing temporary fans under your crawlspace can help to dry out the area and reduce moisture, but we'd wait to do this until you're sure no more water is permeating the area. Insulation under the floor is always a good idea (keep in mind the insulation vapor barrier should face up (towards the floor), not down towards the crawlspace.

Finally, check the moisture content of the joists and other nearby wood members using a calibrated hygrometer (building inspectors or civil engineers should have such a device). Moisture content over 15% can support growth of micro-fungi, whereas 20% moisture or greater is a red alarm, and will result in wood rot over time. By comparison, I checked our home recently using a Protimeter Mini, and the moisture content of the joists in the crawlspace was well below 10% -- a good figure. Take care of your moisture problem immediately. High humidity levels will damage your home and could impact your health.

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