By Walter Jowers

JUNE 22, 1998:  Building a house "high and dry" has been the prime directive of homebuilding ever since our knuckle-dragging forebears moved out of the caves and started building their first shelters out of rocks and sticks. But even now, some builders haven't gotten the message. Just last week, I saw a brand-new house that had been constructed on a swampy lot. There were several inches of standing water in the crawl space, and the backyard was a shallow pond. A few more hard rains, and the builders might as well put in a boat ramp and stock the place with catfish.

A wet crawl space is a bad thing for a whole lot of reasons. Here are just a few:

• When water runs into your crawl space, it can cause erosion, which can slowly destroy your foundation.

• Damp crawl spaces make a dandy habitat for wood-destroying fungus. Given just the right temperature and humidity--and enough time--fungus can eat the wood that holds up your house.

• High humidity in the crawl space can make wood-strip flooring inside the house curl up at the edges.

• Humid air from the crawl space can leak into the house and cause your air conditioner to work longer and harder.

In our part of the world, the cure for a wet crawl space is usually a "positive drain." I've been in new houses during the buyers' final walk-through, and I've heard the builder's rep say these very words: "Don't worry about that water under the house. We'll put in a positive drain."

The buyers just nod, like that's the best idea in the world. It's a drain, right? That's good. And it's positive to boot. Heck, what could be better than a positive drain?

Wet-crawlspace victims, listen to me: A positive drain is not some foolproof, high-tech system. It's a hole in your foundation wall. It doesn't keep water out of your crawl space. It just gives the water that's already there a way out. Sometimes--shoot, most of the time--it doesn't even do that.

When you hear that a house has a positive drain, it means the lowliest, least capable worker on the job site was ordered to crawl under the house and dig some little trenches that lead to the lowest spot in the crawl space. At that low spot, he knocks a hole in the foundation wall to let the water out. If it's a really classy job, he'll dig a little trench from the hole out into the yard. Then he'll stick some plastic drainpipe in the trench, throw some dirt over the drainpipe, and plant grass over it.

Assuming that all this is done right (which it usually isn't, because no skilled people ever check the work), a positive drain can do some good. It does let some water out, so the humidity in the crawl space might be lower. Fungus won't be so likely to grow, floorboards won't be so likely to cup, and the air conditioner won't have to fight the excess humidity.

But a positive drain doesn't address the erosion problem. Even with a positive drain, water will still seep under--or through--the foundation walls. Slowly but surely, this seeping water will weaken the foundation. Consider this: The Grand Canyon was caused by erosion. And the Grand Canyon has a positive drain, namely the Sea of Cortez. Clearly, a positive drain does not give good long-term results.

Over time, the little trenches that make up a crawl space drainage system collapse or fill up with silt. When that happens, the drain isn't so positive anymore, and the crawl space fills up with water again.

The fix for a wet crawl space is to build the house right in the first place. Simply put, this means building on a high spot rather than a low spot. In some new developments--like the one I saw last week--builders run out of high spots but keep building anyway.

Of course, this country wouldn't be what it is today if we couldn't build houses on swampland. We can do it, alligators be damned. But the trick is to do the prep work up front and fill the swamp before you start building. Trying to get the water out from under the house after the fact is a lame idea, and I've never seen it work.

Visit Walter's Web site at http://www.nash-scene.com/~housesense. Or e-mail him at walter.jowers@nashville.com.

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