Insulating crawl space walls and floor keeps out cold and damp


Q: I want to insulate the crawl space under my house and am confused about several points. The crawl space has a dirt floor. Should I cover that? What other advice can you give me?

A: Two systems can be used to insulate crawl spaces. If the space has tightly constructed walls and contains heating ducts or water pipes, the walls should be insulated. In this system, blanket-type insulation generally is fastened to the wood rim joists on top of the walls and draped vertically over the walls. The insulation should extend across the floor for about 2 feet.

In the other system, used in crawl spaces more open to the weather, the insulation is installed between the wood joists of the ceiling over the crawl space. Strips of blanket-type insulation are tucked between the joists and generally are held in place with wire.

Unfaced (no vapor barrier) insulation is used for walls. For ceilings, the insulation should have a vapor barrier attached. The vapor barrier should be turned toward the top or heated area.

Regardless of whether the wall or the ceiling is insulated, most experts recommend that the floor of the crawl space be covered with a moisture barrier of heavy plastic. This is especially important if the crawl space has a dirt floor. The purpose of the plastic is to help keep ground moisture out of the crawl space and living areas of the house, where it can cause such problems as condensation and mildew.

Q: I recently bought an antique oak dresser that has a musty smell inside. All the wood inside is unfinished. I've tried washing the wood to remove the smell, but it hasn't helped. Any ideas?

A: I'd remove all the drawers and put them and the dresser outside for several days. Put the parts where they get lots of air and filtered sunlight, such as under a tree. Bring the wood indoors if rain threatens, of course.

After the sun-and-air treatment, I'd seal all the bare wood surfaces with a couple of coats of varnish or shellac. The sealer will help keep any remaining odors in the wood.

Q: We had a cedar deck built last year and were told by the builder to treat it with Thompson's Water Seal. We applied the seal with a spray tank, once in July and once in September. The whole deck became very sticky, and in the spring we had to clean it with a deck cleaner. What went wrong?

A: The stickiness was no doubt caused by application of too much sealer. Thompson's recommends a first coat of Water Seal at the rate of 200 square feet (a 10-foot by 20-foot area) per gallon. The second coat should be applied in 24 to 48 hours at a rate of only 300 square feet per gallon.

If sealer makes a deck sticky, the best treatment is to wipe it immediately with mineral spirits (paint thinner).

There are many sealers and sealer-preservatives available at home centers and paint stores. Typical sealers are basically water repellents; they help protect the wood against splitting, warping and other water damage. Ordinary sealers do little to help retain the original color of the wood.

If you want a coating that will help preserve the cedar's color, Thompson's recommends its Wood Protector rather than Water Seal.

Q: I have an attic ventilating fan in the roof of my house and several vents in the gables of the attic. Recently I had new roofing installed, and a continuous ridge vent was installed at the peak of the roof. Do I still need the gable vents for the fan to work properly?

A: Ridge vents generally work best in combination with soffit vents, located under the eaves or underside of the roof edge. If you have soffit vents, you might not need either the attic fan or gable vents now. The installer of the ridge vent should be able to advise you. If not, find out who made the ridge vent and write the manufacturer for advice.

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