Our home has blown-in insulation on the foundation block in the crawlspace. I've never seen this before. The other homes in the area I've seen had foam board glued to the wall. There doesn't appear to be a vapor barrier between the block and the insulation, so I'm worried about it holding moisture. Is the blown-in stuff acceptable?

I live in Middle Tennessee where we have a lot of humidity and 90-100 degree temps through summer. In the winter we have several periods of freezing weather with a few snows.

  • 2
    Vapor barrier goes on the warm side: if you put it on the cold side, the warm inside air will condense on it, and get the insulation wet, reducing its insulation value and potentially allowing mold to grow. On the warm side, the insulation prevents the warm and cold air from meeting directly, and no condensation forms.
    – gregmac
    Commented Aug 28, 2011 at 3:20
  • Is the crawlspace conditioned (heated/cooled by your house's HVAC system)? Is it accessible via an interior door/wall to the living space of the house? Are there vents to the outside in it? What is the floor made of?
    – gregmac
    Commented Aug 28, 2011 at 3:22
  • Crawlspace is not conditioned. There is an access door from the outside and several vents. The floor is plywood. Some of the block is below grade which is why I'm concerned.
    – Josh Bush
    Commented Aug 29, 2011 at 0:52
  • 1
    By "blown in" do you mean spray foam or loose fill? Commented Aug 31, 2011 at 15:10

1 Answer 1


Since it's vented outside, the humidity level in the crawlspace is generally going to be equal to the humidity level outside. You should not have any vapor barrier on the walls, as this will actually prevent drying and hold the moisture in (though because it's vented, it will still eventually equalize).

What you should have though, is a vapor barrier and insulation on the roof of the crawlspace, before the subfloor of the floor above. This is an area where cold (air in the crawlspace) meets hot (from the conditioned room above), and so there needs to be a thermal break (insulation) and a vapor barrier on the warm side of the insulation.

I suspect the insulation in the crawlspace itself is just to help slow the temperature changes in the crawlspace, because that's about all it's doing. Considering it's open to the outside, it will eventually get to the outside temperature. Expecting it to add any insulation value to your living space is about the same as leaving your front door wide open and expecting the insulation in the rest of your house to keep you warm.

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