Wednesday, February 1, 2012

Fiberglass Insulation In Your Crawl Space???

I have inspected many crawl spaces over the last ten years, and the question comes up more often than not. Should I install fiberglass insulation in my crawl space? The answer to this question is not a simply yes or no. A lot of it depends on where we are talking about installing this fiberglass insulation and what the conditions of the crawl space are. If we are talking about installing fiberglass insulation on the foundation walls of the crawl space than my answer for that is always no. Foundation walls in a crawl space tend to seep moisture or water. This moisture or water is then soaked into the fiberglass insulation like a sponge. The fiberglass insulation installed all the foundation walls can also allow moisture or water to wick upwards towards the structure wood components of the house in the crawl space. This in return can lead to mold growth or possible wood rot. Now if we are talking about installing fiberglass insulation under the sub-floor, between the floor joist in your crawl space than my answer is yes, but only if certain conditions are meet. Fiberglass insulation installed between the floor joist can also work like a sponge and absorb moisture and hold it between the structure wood. But if the crawl space is conditioned right so that moisture is no longer a problem in your crawl space than fiberglass insulation between your floor joist can be beneficial. In order to make sure moisture is not a problem in your crawl space before you consider any type of fiberglass insulation you might want to consider some type of encapsulation system for your crawl space first. An encapsulation system in your crawl space would be the best method of eliminating any moisture before you install fiberglass insulation. To find out more information about crawl spaces please visit


  1. I know great crawlspace insulator contractors in Durham that use spray foam. It is great for waterproofing.

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  3. After reading your article, I have decided to install fiberglass insulation in my crawlspace. I can understand why you wouldn't want it on the foundation walls, but that is not my intention. I want to place it under my sub-floor. I carefully considered your warning, but I think I have the moisture under control.

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