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Evaluating Crawlspace Insulation

May 25, 2013 | Posted by Mitt Jones

It’s easy to conclude that you need crawlspace insulation if the joist bays above your ventilated crawlspace are empty. How do you make the choice when there is already some insulation installed? How do you know if what you have is good enough?

Cold Feet

One easy test is how the floor feels. If the floor feels colder than it should, chances are your insulation isn’t performing well. Especially if your floors are carpeted, however, you may be losing lots of heat without noticing a difference.

If you’re up for an adventure, slip into working clothes, grab a flashlight (a headlamp works well), put on a dust mask or a respirator, and head into your crawlspace to take a look for yourself.

Scary Things

First things first: If you see or smell animals, dead or alive, close up the hatch and call a pest control company—especially if you can see where animals would be getting in through torn vent screens. Raccoons, especially, can be aggressive when cornered.

Now to the insulation. If the fiberglass batts are sagging badly or falling in places, you know you have a problem. Your insulation can’t do its job if it’s not in place or if unconditioned air can flow freely around it.

If the insulation looks shredded in places and you see holes burrowed into it, you may have a pest problem. Depending on the extent of it, replacing the crawlspace insulation might be in order.

Batts and Gaps

Let’s say the insulation looks pretty good and you don’t see any obvious signs of pests. Slip a hand between a batt and joist to see if there is an air gap above the batt. If there are two batts running side by side between beams, slip a hand between the batts.  

Ideally, the fiberglass batts will be held snug against the wood subfloor above them, but having an air gap above the insulation doesn't make it completely useless. In fact, as long as the insulation fits fairly tight between the joists or beams, having an air gap might make the floor feel warmer. On the other hand, if ill-fitting batts are hanging inches off the floor, your insulation probably isn’t working very well. 

If your crawlspace insulation isn’t being held snug against the floor, it may be practical to push it up into place by adding more insulation below it. This only works if the existing insulation is well supported, though, and adding more insulation can be a trying task even in the best of circumstances.

If the existing insulation isn’t working well, we generally recommend removing it and installing new insulation from scratch. This allows the installers to provide the best-quality installation. It also allows clear access for air sealing. 

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