Making crawl space on home waterproof

Q. We are building a small home on an Arkansas hillside and want to waterproof the crawl space within the concrete-block foundation wall. How shall we go about it?

* Also, we installed R-19 fiber-glass batt insulation with a vapor barrier between the rafters. Would cutting slits into the vapor barrier be the right thing to do before we add additional batts? Additional batts below could be the same vapor-barrier type, but without the barrier. A reader Tulsa, Okla.

A. Crawl spaces above grade require practical means to keep moisture from migrating from outside. Install perforated footing drains to "daylight" on the upper side of the foundation. This will intercept rainwater from above.

Install gutters and downspots. which will compel the rainwater to run away from, not toward, the foundation.

To put the icing on the cake, so to speak, install 6-mil polyethylene sheets in the crawl space right on the ground. Tape the joints. Run the sheet ends up the inside of the foundation wall and tape them there. This prevents any stray moisture from coming up through the ground and into the crawl space. Then maintain good crawl-space ventilation. The upshot is that you will have licked the humidity problem there.

* Now about the roof insulation:

"Additional insulation should never be installed over a vapor barrier located in its proper position toward the warm side of the wall, ceiling, or floor," says Kenneth d. Mentzer of the Mineral Insulation Manufacturers Association, 382 Springfield Avenue, Summit, NY 07901. The phone number of the organizations is (201) 277-1550.

"The vapor barrier shoud be removed or destroyed prior to the addition of insulation," he adds.

Regarding roof ventilation, it may be necessary to provide a ventilated space between the insulation and roof deck. This will allow any moisture that may pass through the ceiling assembly a means of venting, thereby avoiding the possibility of condensation on the underside of the roof deck.

"We would recommend that your reader contact the local building department for its recommendation on this matter," Mr. mentzer concludes.

You can write to the association and ask for a free copy of a booklet entitled: "How to Save Money by Insulating Your Home."

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