Can Fiberglass Insulation Be Reused? – Myth #7

This week we’re continuing our myth series about recycling/reusing the insulation in your crawl space.

Reusing Crawl Space Insulation

Whether out of lack of knowledge or pure laziness, there are a lot of crawl space companies out there who will reuse the fiberglass in your subfloor. They will pull the insulation down to the ground, spray the joists with mold disinfectant, and then take the insulation off that nasty, nasty ground, after it got covered in mold and disinfectant, and shove it back up in the floor joists and say, “See you later Mr. Homeowner.”

Well, that’s a myth. We don’t recommend that you ever, ever let anybody recycle your insulation between the floor joists. Here are a few reasons why…

Why You Should Not Reuse Insulation

There’s a good chance that if the contractor was in such a hurry to complete the job that they didn’t replace the insulation, they also did not give the floor joists time to properly dry after applying the mold disinfectant.

If you place fiberglass insulation back between the joists while the disinfectant is still wet, you won’t be giving the disinfectant the time is needs to work against the mold and fungus growth properly and you will also be trapping the moisture. This could cause you more problems in the future.

How To Insulate Your Crawl Space Subfloor

Sometimes we’ll have a job where the homeowner wants to keep their subfloor insulated and not insulate the foundation walls with foam board. What we’ll do is take the insulation out and we dispose of it completely, treat the mold, let the disinfectant dry, and then install NEW fiberglass insulation that hasn’t been sitting in the dirt and debris of the crawl space floor the entire time.

Don’t recycle insulation! We call that a crawl space myth and we hope you found this helpful.

4 thoughts on “Can Fiberglass Insulation Be Reused? – Myth #7”

  1. Can I place insulation board Omer my joist bottoms for insulation. The prior owner had batts and pulled them down due to mold growing in the joists. They put down plastic but did a poor job and the water heaters leak. So I have to fix the moisture problem and want to buy a crawl space dehumidifier from you. About 3400sf floor space heater and cooled. Crawl space is mostly above ground and 4-6, high.

    1. Hi John, yes this can be done but keep in mind it can still trap moisture if environment is humid or you get a leak from above. We try to insulate foundation walls vs sub-floor when possible. Hope that helps.

  2. I just bought a home and am currently remodeling I have two vents on either side of my home from the crawlspace, no moisture issues. There does not appear to be any insulation in the crawlspace. There was also roofing paper covering the subfloor which is another issue entirely. What would be the first steps to getting the crawlspace headed the right direction?

    1. Hi Patricia, Depending on what part of the country you live in may determine the steps to follow but I would purchase a remote humidity reader to see accurately what the relative humidity is during the summer. People tell me they don’t have moisture issues but they are referring to standing water or flooding. High humidity is considered a moisture issue as well but sometimes is not as apparent. If your crawl space has high humidity, I would follow the Crawl Space Encapsulation Guide as closely as your budget allows. Focus on moisture issues 1st. If the roofing felt is above joist and below the sub-floor and it is causing harm, I think cutting it out is about the only option. Hope that helps.

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