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Which insulation is best for crawl spaces?

Answered by Jeffrey Anderson ~ March 1, 2013 ~ No Comments

I have a crawl space under my kitchen. It has an entrance, but the floor is so close to the ground that there's no way I can squeeze in to insulate between the joists. The floor of the crawlspace is dirt and has no vapor barrier, though the ground seems pretty dry. How can I insulate without pulling up the floorboards completely?

Jeremy

Jeffrey Anderson

Jeremy, crawl spaces are a bit of a gray area in many building codes in that minimum heights are often not specified. In some cases the only mention of height is that floor joists must be treated for moisture resistance when in close proximity to the ground. And even if modern code had clear and defined minimum height requirements for crawl spaces, there are many in older homes that probably wouldn't pass.

Fortunately, even the smallest crawl spaces can usually be insulated -- although it's not always an easy task. I see two issues that should be addressed with the space under your kitchen: it should have a moisture barrier installed over the dirt floor, and some type of insulation needs to be applied to the perimeter walls or between the floor joists.

The best location for the insulation is dependent on whether there are vents in the perimeter foundation walls that allow unconditioned air into the space. If there aren't any, then insulation can be applied to the insides of those walls to create a conditioned space. This is the best scenario if you have plumbing pipes or ductwork under the kitchen floor.

However, if there are vents, then the insulation should be placed between the joists to prevent unconditioned air from reaching the floor. I would think that any house in Michigan with a vented crawl space would have any plumbing lines or ductwork in the area already insulated or there would have been problems long ago. But if for some reason your home doesn't have this protection, insulation should be applied to anything of that type that extends below the joists.

As to the type of insulation, it sounds like closed cell polyurethane spray foam might be the best choice. This type of insulation provides a very high R-value per inch and doesn't require much in the way of access for application. I suggest contacting a few insulation contractors in your area that offer the product and asking them to make a jobsite visit. That should allow them to address any possible accessibility issues and also figure out how to place a moisture barrier in the space prior to providing a price for the project.

One word of caution: choose a contractor who provides a warranty for the spray foam insulation and their work. It's also a good idea to check references from past jobs that were similar in nature to yours.

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