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Community and Q&A

Cost-Effectiveness of Air-Sealing and Insulating

david_solar | Posted in General Questions on

Hello Everyone, My wife and I bought our first home two and a half years ago in MA after chatting with some people on the boards here, and since that time we had a contractor come in to address the basement. It had loose fiberglass bats in the ceiling, and we replaced that with rigid foam against the bare concrete walls and spray foam to cover the joists (I think that’s what they’re called where the top of the foundation walls meets the wood.) The basement is warmer, but not incredibly so, and it was an expensive undertaking. My wife wants to deal with our bedroom next. It’s a finished room over a garage, and it’s cold in the winter and warm in the summer. There’s loose fiberglass batts between the garage ceiling and the floor of the FROG, which could definitely be improved with some dense fill cellulose, the kneewalls of the room could use either spray foam or foamboard + dense fill cellulose, and the attic is exhausting to even think about. It’s ~1600 sq. feet with loose fiberglass, and while the roof was constructed well, we’ve got HVAC runs up there and the builders didn’t air seal anything. Ideally we would pull out the fiberglass, air seal everything (we know it’s leaky because the insulation closest to the floor is dirty as heck), and then blow in new cellulose. The main bedroom and attic are big spaces, and there’s nothing I can do about that, but the quotes I’m getting seem nuts to me. One contractor with a good reputation quoted me just north of $35K to address all the components I mentioned above, and said it was probably two weeks of work. I can’t even find a second person who’ll do things the way I want – the spray foam guys want to spray everything everywhere as thick as I’ll let them, and the cellulose guys don’t want to airseal. MassSAVE came and did an audit when we moved in, the blower door test was good enough that they wouldn’t subsidize any of the work for us. The house isn’t super comfortable, though. Are there any options besides shelling out tens of thousands of dollars? My wife and I are professionals with young kids, and even just doing the math on how many bags of cellulose I’d need for the attic combined with how much the rental blower can shoot out put it at 18 hours of uninterrupted time for that one thing alone. I don’t have time for that. Should I just go up there myself and spend 30 minutes a day in a tyvek suit, moving insulation, airsealing with a can, and moving the insulation back? I’d really appreciate any advice you all can offer. Thank you! NOTE: For reference, more than one person has told me it’s ~$2,500 a day to get a cellulose truck at your house in my area.

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  1. nickdefabrizio | | #1

    I will leave it to others on this site with more experience to discuss these options. One point I am familiar with is the garage ceiling under your bedroom floor. Code in some districts requires double 5/8 sheetrock on garage ceilings under bedrooms. This can be undertaken at the same time you air seal and reinsulate this area. Reducing air leakage between the two spaces is a good thing for health and safety as well as energy efficiency and comfort. My only point in raising this is that you should be considering this issue as well as you contemplate removing the ceiling in the garage. ....

    A family I know had a similar problem to the one you describe.... In their case, it seems that the added finished room never got enough air CFM from the main HVAC system to properly heat and cool the large bedroom. You might revisit the HVAC system to see if a stronger but more efficient system is an option. Or you could think about adding an efficient mini split for just this room. Neither option is cheap, but may qualify for a rebate under the Mass clean energy plan.

    1. david_solar | | #2

      Hi Nick - I wouldn't remove the ceiling, I'd have a contractor drill holes through the drywall in each bay and put in dense-pack cellulose that way. The cellulose just compresses the existing batts. They seal and spackle when they're done.

  2. Expert Member
    Akos | | #3

    The $35K sound like a go away price, the guy just didn't want to do it.

    Most major thermal comfort issues are from air leaks, so that is what you need to fix first, getting extra insulation in there doesn't hurt but won't help much.

    I would break the job into a couple of manageable chunks and have a contractor bid for each section. First would be to pull the ceiling in the garage and insulate the floor with spray foam. While the SPF guys is there have them spray and encapsulate your ducting and registers and lights in your attic (this means raking the existing insulation away, but not a huge job).

    If you have knee walls, you also want them to seal up your floor joist/wall intersection with SPF as well. If you can do it from the garage bellow, that is great, if not you need to do it form the attic side which is no fun.

    Once the SPF is done, re-install the garage ceiling. I would hang the ceiling on resilient channel to reduce noise transfer upstairs plus mount the motor and track onto rubber isolation mounts.

    Provided you get decent flow through the ducts, this would probably solve most of your comfort issues and you need only four subs:

    -demo/rake insulation away
    -re-install garage door hardware

    1. david_solar | | #5

      Thanks for the thoughtful reply, Akos. Are you saying I'll get much better results with removing the garage ceiling, spraying it, and reinstalling the ceiling vs. adding dense pack cellulose in the existing assembly?

      1. Expert Member
        Akos | | #6

        A good dense pack does seal things up pretty well. Not as air tight as SPF but good enough.

        The reason I suggested SPF is it sounds like there are a lot of complicated shapes, making sure that all nooks and crevices are dense packed properly and sealed would be a challenge. With the ceiling off, you can see these issue and deal with them directly plus you can get the spray foam guy to touch up the questionable areas in the attic where dense packing won't work.

        A nice bonus is that you'll get a much better air seal between the garage and the rest of the house as well as usually no attempt is made to air seal above garage partition wall and the bonus room floor joists.

        I usually try to avoid SPF, I think in this case it makes insulating and air sealing much easier.

        Since your utilities are not that expensive, the lower cost option would probably be to throw more heat at the problem as suggested earlier. Either see if you can bump up the air flow on the existing ducting or install a dedicated wall mount mini split.

  3. Deleted | | #4


  4. david_solar | | #7

    Bumping this as I've received a few quotes from different vendors. I'm not sure what to do with the numbers because the quotes aren't directly comparable.

    Vendor 1 - $5k just to remove the loose fiberglass & batts in the attic. Their thinking is that by doing that, I would fail the blower door test which my home passed three years ago (it's a very low standard) and then the MassSave program would subsidize all the air sealing and new cellulose in the attic. This is basically fraud from what I can tell, plus there would be some period of time where I would have zero insulation in my attic in Massachusetts in wintertime.

    Vendor 2 - $12.5k to remove attic insulation, spray foam roofline of attic to R-38, spray foam kneewalls and end gable walls of the bedroom over the garage to R-28, and block off the roof soffits with some proprietary thing they can foam directly over

    Vendor 3 - $3,100 to add 5" of cellulose to the attic (no air sealing), add 2" of foamboard to the kneewalls where there's currently batts but no vapor/air barrier, and dense-pack the ceiling above the garage (the bedroom floor)

    I'm not sure what to do here, honestly. It seems like dealing with the non-foam guys to air seal where there's existing loose fill fiberglass is just really pricey, which is why they don't want to do it - or are being sketchy about it. The spray foam came in lower than I expected, but turning the attic into conditioned space makes me nervous about moisture issues.

    Any more words of wisdom as to how I should proceed? In other news, we are closing on a piece of land up in Maine and you can bet I'll be airsealing the heck out of that slab-built, one-story, superinsulated house :)

    1. Expert Member
      Akos | | #8

      Loose fill fluffy insulation does almost nothing for air sealing. Removing all of it will barely budge your ACH@50Pa.

      None of the options really fix all the issues with a leaky bonus room. The SPF option comes to closest but that is a lot of money for something that can be potentially fixed with a couple of sheets of rigid insulation, canned foam and a lot of elbow grease.

      It doesn't sound like this is your forever home, I would not spend a lot of money fixing a comfort problem. I would say an in-between solution would be to just dense pack the floors and bump up the HVAC feeds to the room. You can try just dense packing by itself as it might get the place to good enough comfort for the short term.

    2. Trevor_Lambert | | #9

      Even if you could make the house fail a blower door test, won't they question why the house got worse from the previous audit? Not just fraud, but obvious fraud. Terrible suggestion.

    3. Expert Member
      BILL WICHERS | | #10

      I agree option #1 is bad news. It's definetely fraud, and you really don't want to open that can of worms. The other two options are honest options, so I'd go with one of those or something completely different.

      Spray foam is good when you have to seal something you can see but you can't reach. This might include confined spaces out near the eaves, for example. This isn't one of the niche applications where I would normally recommend spray foam, but in your case it may actually be the best option. I would use closed cell here, and the reason for that is you get a better air barrier with a thinner layer of closed cell, and you're likely to have a hard time getting a good application in a confined space. My crew has had issues before in areas like this because they can't maneuver the foam gun and hoses to get a good angle to spray some areas, which makes it very hard for them to get even applications in some spots.

      Cellulose is much better at acting as a bandaid for poorly air sealed attic floors compared to other forms of loose fill insulation. If Akos is correct, and you're not planning to stay in this home long term, option 3 might be your best bet since it will probably help, although it won't be optimal, and it's a lot cheaper than the other options.

      When you get ready to build your new place in Maine, come ask us Q+A people lots more questions :-) It's a LOT easier to do a good job of air sealing when you're planning it from the beginning. Just make sure your PLAN includes the air sealing and envelope stuff -- don't try to do it after framing starts. Plan to build a tight home from the beginning and everything will be easier, and also cheaper, to do right.


      1. david_solar | | #11

        Thanks to all three of you for your thoughts - I think we're going to go w/ option #3. The guy who came to the house was the owner, a licensed ME, and seemed like a straight shooter. I expect that adding more insulation beneath the floor and putting an air barrier on the kneewalls will improve comfort a reasonable amount without a huge expense. I'll update the thread later and let everyone know the outcome!

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