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Community and Q&A

Whole-House Air-Sealing and Encapsulating Crawlspaces

kieran973 | Posted in General Questions on

About a year ago I moved into a 1925 house in southern CT with zero insulation. Through a state rebate program, I had two separate companies add what I thought was a good insulation solution to the attic and basement, only to find out later that they didn’t do any air sealing: the main attic (walk-up) is R-49 but with no air sealing (half blown in cellulose under the floorboards, half fiberglass batts on top of the floor); the foundation rim joist is R-15 (mineral wool batts) but with no air sealing; and the main (larger of two) crawl space is R-11 (XPS Foamular 250) but with no air sealing. A big part of this is my own ignorance — I didn’t understand the importance of air sealing and therefore didn’t insist on it. But many on this forum educated me about its importance (ie: Akos especially) and so last spring I set out to find a contractor who could do some air sealing.

For months I couldn’t find anyone who would do this. Every contractor who I made an appointment with for an air sealing estimate kept the appointment, came to the house, and then said “we don’t do air sealing — we only do closed cell spray foam jobs, that’s our air sealing.” But finally, this month, I was able to find a company in my area that offers whole-house air sealing.

I had an appointment with them last week. They did a full energy audit which involved a blower door test (3073 CFM). They get excellent reviews and I like all the people there that I’ve interacted with. In addition to the whole-house air sealing, they’ve proposed a number of other insulation and encapsulation jobs. This proposal is the following:

1. Whole-house air sealing with a guaranteed reduction to a maximum of 2,000 CFM

2. discarding all existing attic insulation and using Heatlok HFO to insulate the walls and ceiling of my main attic as well as three smaller “side” attics over my kitchen, front door, and first-floor bedroom/bathroom (it’s a “1.5 story house” where several parts of the second floor exterior walls are not flush with the first floor exterior walls)

3. using Heatlok HFO to insulate the rim joist (and discard the mineral wool batts)

4. using Heatlok HFO to “fully encapsulate” the walls, ceilings, and floors of our two crawl spaces: the “main” crawl space underneath the first-floor bedroom, and a smaller crawl space underneath the front door entrance and an a walk-in closet.

To be honest, I’ve been trying to avoid putting spray foam anywhere in the house in any capacity, for the standard reasons: 1.) toxicity/cancer, 2.) GWP, and 3.) the possibility of catastrophic property damage if done wrong. But I’ve been getting worn down on this position, especially when it comes to the rim joist. Our rim joist is very leaky, but it’s also so irregularly spaced and packed with pipes and wires that the cut and cobble foam board method would take a really long time. I keep asking contractors if they’d be willing to use Visconn, or any low-VOC product for that matter, but I can’t find any actual real people willing to do that: they all just say no, we use spray foam. So after 15 months, it’s looking like the only realistic options for the rim joist are either spray foam or nothing, at least not anything with an air barrier. So what should I do? Just spray foam the rim joist? Leave the mineral wool batts in there? Take out the mineral wool batts and just live with an un-insulated and un-air-sealed rim joist?

As for the attic insulation proposal, I’m not ready to insulate more in the main attic yet because we’re in the process of trying to finish it off and I don’t want to do anything that we might just un-do later (like with a shed dormer, for example). In terms of the minor “side” attic insulation: are there any good alternatives to spray foam? Would blown in cellulose be a mold/wood rot issue? I don’t believe there is any insulation at all in those attics currently, though there’s no access to them, so I’m not sure.

As for the crawl space encapsulation proposal, I was a little surprised to hear this company propose encapsulating our main crawl space (under the first-floor bedroom and bathroom), since I’ve already done a lot of work in there: we paid $1800 for a 16 mil vapor barrier last summer that I thought already was an encapsulation; plus we had the foam board put in on the crawl space walls. But this current company wants to just cover all of that with Heatlok, as well as the ceiling. Does this make sense?

The smaller crawl space (under the front door and walk-in closet) is something that I do have to deal with. I didn’t even know it existed until a few months ago, and it’s a mess: dirt floor, piles of old fiberglass batts, beer cans, etc. But do I need to deal with it with Heatlok, or could I just clean it out and put down another vapor barrier plus some more foam board on the walls (I would go with EPS this time)? What about concrete on the floor instead of spray foam? It seems a little excessive in terms of GWP to put spray foam on the floor of anything, but I clearly know very little about crawl space encapsulation if I thought that a vapor barrier on the ground and few feet up the walls made our main crawl space already encapsulated.

Sorry for all the questions. I’m a little overwhelmed by all the different aspects of this proposal (the best way to insulate small side attics; the best way to encapsulate a crawl space, etc.). Any guidance on any (even just one) of these issues would be appreciated.

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  1. brian_wiley | | #1

    Hi Kieran,

    What type of foundation (concrete, stone) do you have? And how deep is the crawlspace?

    1. kieran973 | | #3

      It's a fieldstone foundation. The crawl space is about 4 feet deep. Thanks.

      1. kieran973 | | #5

        Sorry, I should clarify that the main crawl space (under the first-floor bedroom/bathroom) is about 4 feet deep while the small crawl space (under the front doorway and walk-in closet) is probably 2 feet deep.

        1. brian_wiley | | #6

          I asked because i feel like there’s something I’m missing. I can understand why they may want to spray foam the fieldstone foundation, but I don’t quite understand the logic behind spraying both the floor and underside of the subfloor (crawlspace ceiling).

          My understanding of things could be wrong, but I would assume that Heatlok on the walls (and rim joist) to a thickness commensurate with your climate zone along with a vapor barrier on the floor with taped seams would be sufficient. The floor foam would be optional, but not necessary I believe. Then, some sort of conditioning strategy as per the code (dehumification, exhaust + makeup air from the living space, or HVAC return/supply) and you’d be set. No need to spray the crawlspace ceiling.

          Hopefully one of the more experienced members and confirm (or totally blow up) my assumptions.

  2. Patrick_OSullivan | | #2

    Couple of things:

    - Demilec Heatlok HFO uses Honeywell Solstice as its blowing agent, which has a GWP of 1 (

    - You could consider AeroBarrier as a way to get air sealing, and eliminate/minimize use of spray foam:

    1. beedigs | | #7

      Is AeroBarrier paired with open cell spray foam for cavity wall insulation @ exterior wall be overkill? climate zone 2

  3. kieran973 | | #4

    Yes, I was glad to learn that about Heatlok HFO. I did contact the only AeroBarrier dealer within 100 miles last spring, but they said they only use it in empty houses with no people or furniture. Anyway, thanks for the tip.

  4. user-7837250 | | #8

    So did you go with any of this? How did it turn out?

    1. kieran973 | | #9

      Haven’t done anything yet, no. I got frustrated and moved onto some other projects - mini-splits, solar battery, roof repair, etc. All of those are done so I’m just now returning to the rim joist issue. I’d prefer to do Visconn + mineral wool + vapor barrier, but can’t find any contractors willing to do so. And the rim joist is irregular/annoying so I get why. Plus the small crawl space is so short I’m not even sure someone would have the room to do a good job laying a vapor barrier on the ground or carefully applying Visconn to the rim joists - the only solution might be just standing on a ladder outside the small opening and spraying the short walls and rim joist with a long spray foam gun.

      Currently, all I have is what the insulation company did in spring 2021: mineral wool batts in the rim joist bays, no air sealing, no vapor barrier.

  5. user-5946022 | | #10

    Are both of the crawl spaces relatively dry?
    Is there a discernable comfort issue in the house? (leaky, drafty, other)

    I might be inclined to address those two issues, but beyond that, the work probably won't pay for itself. So another approach is to address organically as you do projects such as you mentioned for the attic. The fundamental problem is many workers just don't care much about quality, so you spend all this money and get a 1/3 it does not do what you really intend.

    Tell the Aerobarrier folks you will make your crawl spaces empty with no people or furniture, and you want a quote on sealing...

  6. mdhomeowner | | #11

    Your reasons for staying away from spray foam are good ones, don't give up that position.

    It's unfortunate that you haven't found a good contractor yet that will do air sealing. I've seen it done effectively with caulk and foam boards, which you can get low-VOC versions of.

  7. kieran973 | | #12

    So the Visconn specs say the thickness is only 1/8 inch. But I thought you needed an air barrier of 1-2 inches (I’m in climate zone 5). So would it work to air seal/insulate the rim joist this way: 1/8 inch Visconn air barrier, 2.) mineral wool batts over the Visconn, 3.) Drywall over the mineral wool batts?

    1. Deleted | | #13


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