Q & A – Crawl Space Insulation

Hi Philip,
Our home has a crawl space underneath it with deteriorating fiberglass insulation that needs to be replaced. Can we use a “green” insulation in the crawl space?
— Geoff & Barbara, Oakland, California

If your fiberglass insulation is deteriorating, make sure you have adequate crawlspace ventilation. Mold and bugs do not eat fiberglass, so the deterioration is likely caused by moisture accumulation that has collapsed the air spaces between the fibers — your insulation is probably getting wet. If that’s the case, your new insulation will soon deteriorate as well.

Building codes require that you have a certain number of square feet of ventilation for every square foot of crawlspace. Find out what the code ratio is for your area by calling your local building department.

Then measure your basement vents and compare them to the square footage of your crawl space. You should have at least as much ventilation as is required by code, and ideally more — especially if you live in a moist climate.

Cutting holes into an existing house to add ventilation can be expensive. One easy trick is to replace your crawlspace hatch door with a screened door. (Double screen layers work best —one based on _-inch wire mesh to keep animals out, and one regular window screen to keep bugs out .) Building and hanging a new hatch door is simple and cheap compared to cutting in vents, and a typical hatch door is as big as four to six typical foundation vents.

Also, it’s a good idea to place a heavy layer of black plastic on the floor of your crawlspace to reduce moisture and make it easier to crawl .

One “green” insulation that would work in a crawlspace is made from remnants of the blue jean manufacturing process — parts of the cloth that can’t be used to make clothes. Although the cotton from which the product is made is water-and-pesticide-intensive, the insulation itself is made from a “post-industrial” scrap that would wind up as landfill if it weren’t used as insulation. Also, it’s 100 percent nontoxic — you can put your toddler in a pair of blue jeans.

Blue jean insulation is available in batts, so it is appropriate for installation in crawl spaces. (Cellulose “powder” insulation won’t stay in place, and although foam insulation will stick to the subfloor and joists, it is very expensive.) To find out more, google “green insulation.”

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