Crawl space encapsulation question

Old 10-24-14, 06:35 AM
Thread Starter
Join Date: Oct 2014
Location: United States
Posts: 1
Received 0 Votes on 0 Posts
Crawl space encapsulation question

We have a crawl space under half of our house (under the addition, which we think was put on in the '60s). It's a dirt floor, not ventilated. You can squat in it for the most part, but it does slope up at one end so that it's only a few inches from the floor joists at that end (from what I understand from the estimators--I've never actually been in it that far, and there's a large bit of bedrock in the middle that blocks the view of the far end).

We've been in the house for about three years and have never noticed any water issues in it, but we're pretty sure it's contributing to poor air quality in the house, so we'd like to have it encapsulated. (Bonus: better storage area)

So far, I've had two contractors give estimates. Their prices are about the same (although one will include some mold remediation in that), and they're using the same, 20-mil encapsulation material (CleanSpace). Both also include the same commercial-grade dehumidifier (at which I'm cringing because of the cost plus the energy use).

One of them said that they'll be able to completely seal it on all sides, no problem. The other one said that they may have trouble sealing it completely on that far, narrow end, but they'd do the best they could and seal it everywhere they can. I have a concern about each, and I'm not sure which would be worse:

1) If the first one does indeed seal it but in actuality only seals it back as far as they can, that might leave some of the wooden joists sealed outside the encapsulated space. Is that just asking for rot trouble, especially since we won't be able to see what's happening? (Note: He didn't actually say this would be the case. I'm just speculating, since the second guy said it may be too narrow a space back there to do it right. But also, the second guy also didn't try to get himself all the way back in there--he just duckwalked in a bit to shine a flashlight around the boulder.)

2) If we go with the second one and they can't seal it all the way and so they only get the material back in as far as possible and seal everywhere else, is it even worth doing the encapsulation? If it's not completely sealed, what's the point?


(I'm working on getting a third opinion/estimate, but I'm not sure if I'll be able to.)
Old 10-24-14, 07:08 AM
Join Date: Oct 2008
Location: New England
Posts: 10,524
Received 37 Votes on 34 Posts
Welcome to the forum.

I don't have the number at hand but something over 50% of the air you breathe comes from your basement and/or crawlspace. So it does relate to IAQ (indoor air quality).

I read encapsulation but did not see insulation. If you air seal between the rim joist and the foundation, plus all other joints, and then fully insulate that rim and add rigid insulation down to the floor, then you simply share some of the heat from the house and no dehumidifier is needed. You also get warmer floors. What type of heat does the house have and is the rest of the basement insulated?

When it comes to covering all of the dirt floor of only the easy part, go with the skinny contractor and get it all covered. Letting them choose what they can get to opens the door to not know what you are going to get. Going for 100% takes out any confusion and really is necessary if at all possible, even at an extra expense. I'll add a link on crawlspaces.


BSI-009: New Light In Crawlspaces — Building Science Information
Old 10-24-14, 11:02 AM
airman.1994's Avatar
Join Date: Dec 2005
Location: VA
Posts: 5,795
Received 8 Votes on 8 Posts
1st 20 mil is over kill. 6mil would be standard. I would not purchase the dehumidifier at this time. I have only had one crawl space out of hundreds that needed it after we but the vapor barrier down.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: