Q: We live in a 50-year-old home that we purchased last year. Before moving in we removed the carpet and refinished the hardwood floors that had been covered for many years. We also put in fiberglass insulation wherever we had access to open walls and installed it in the attic when the roof was replaced. The only place we have not insulated is the crawl space.

The floor is quite cold and we are afraid that a lot of our heat is lost or diffused from it.

After reading your answer to the homeowner with the soggy crawl space, I would like to lay down the heavy plastic tarp as you recommended. I also plan on installing insulation in the crawl space.

I have been doing some research and have found companies that sell expanding polyurethane foam insulation that can be sprayed. Our crawl space is tight with less than 3 feet of space. I was dreading having to staple or nail fiberglass insulation in such a tight space. However, with the polyurethane foam insulation, it would sure make my job a lot easier besides forming an additional moisture barrier between the crawl space and subfloor. What are your feelings on foam insulation?

A: You’re on the right track. The first thing to do is apply a vapor barrier of 6-mil plastic over the entire crawl space.

If the soil in your crawl space is damp, that means ventilation in that area is probably insufficient. Consider punching a few more vents to ensure that crawl space ventilation is adequate. Finally, insulating the floor joists with R-11 to R-19 fiberglass batts will reduce heat loss through the floor.

We’d be a little leery about trying foam insulation between the floor joists.

Applied to exterior walls in new construction, it’s a good choice. Although foam costs about 20 percent more than conventional insulation, foam gets in all the nooks and crannies, creating a formidable barrier to air and moisture migration between indoor and outdoor spaces. This said, we’re not sure how successful it would be in a crawl space application.

Applying foam insulation is not a do-it-yourself project. It’s sprayed between framing members in liquid form using a high-pressure sprayer powered by a compressor. It’s a job for licensed, bonded and certified professionals. We think attempting to spray foam overhead in a tight crawl space risks creating a gooey mess — although the stalactites that form as the foam expands and dries might create some interesting art.

Rather, we’re more comfortable with the tried and true — especially when doing it ourselves. We suggest you install fiberglass insulation backed with a vapor barrier of either paper or foil between the joists. Installation is easy, if a bit uncomfortable.

Merely unroll the insulation, push it — vapor barrier side up — toward the floor between the floor joists and secure it either with wire or special plastic stays manufactured for retaining insulation overhead.

Q: How do you measure humidity in your house?

A: Humidity is measured with a device called a hygrometer. We found a British Web site with extensive information on these instruments. Go to www.testo.co.uk and type “hygrometer” into the search field.

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