How to Insulate a Crawlspace

LESLIE: Eric in Alaska is on the line with an insulation question. Tell us about it.

ERIC: I have a crawlspace and I’m trying to figure out what the best way to keep the temperature a bit warmer than it is down there and to keep my floors in the home from getting so cold. I’ve got hardwood – ceramic-tile floors.

TOM: OK.

ERIC: And my – all of my plumbing is in the crawlspace. My pressure tank is down there, so I need to keep the temperature somewhat warm down there so I don’t freeze my pipes up.

TOM: OK. How much insulation do you have in the floor above the crawlspace area now?

ERIC: None.

TOM: Is it completely – oh, you have none? Well, see, now there would be a good place to start, Eric.

ERIC: Right, right.

LESLIE: Mm-hmm. And that’s going to make a huge difference.

TOM: So, what you want to do there is if you have – let’s just say your floor joists are 2x10s, then you’re going to use 10 inches of insulation. You want to fill up that entire cavity with insulation. You can use unfaced fiberglass batts. The first place you insulate is the box joists – that’s around the outside perimeter – and then you work your way in to the floor joists.

ERIC: Right.

TOM: You can use insulation hangers to hold it in place. And that’s going to make an enormous difference warming up that floor.

You may find that the crawlspace becomes a bit warmer as a result of that. Or you may find it becomes colder, because now the heat from upstairs is not getting down there. Is there a concern of water pipes or anything like that freezing?

ERIC: Yeah, that’s what my concern is if I insulate the floor there. You know, my pressure tank and all of my plumbing fixtures and drains are all down there.

TOM: You don’t have to worry about the drains freezing, OK? They’re never going to hold enough water to freeze and break. As far as the plumbing pipes are concerned, if you do have pipes that are below the insulation – if they’re in the insulation, you don’t have to worry about it. If they’re below the insulation, then you can insulate those themselves with insulation sleeves that just fit around them and get taped off.

So, insulate the pipes, insulate the floor joists and I think you’re going to find it’s a lot more comfortable as a result.