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Air sealing ceiling options & pros/cons

Nat_T | Posted in General Questions on

Not so much a how question but more bang for my buck input and any foresight into things I may not be considering.

This is new construction, vented roof with unoccupied attic, no mechanicals in attic, no can lights in 2nd floor ceiling.

Not shooting for any particular target but hoping for better than builder house so in the 1.5 ach range.

I realize that air sealing the 2nd floor ceiling and my lowest levels (sill etc) is at the top of my air sealing list. From reading on here I’ve found a few strategies for the ceiling and wondering about the best bang for the buck here.

1) Let framers put up partition walls w/nothing special, rock the ceiling, and then I try to sneak in behind them and caulk all the gyp to plate gaps before they do the walls. This seems like a good diy exercise and this option is the cheapest and least likely to ruffle the contractors feathers. Assuming I’m somewhat competent with this method how effective is this? It’s the most attractive if its reasonably effective.

2) have the ceiling rocked before partitions are up. I’d still need to come around the caulk the perimeter gaps to plates and this is out of sequence. I might be able to convince my framer to just do this rather than have the sheetrock guy come and go – but either way will take some sequencing with guys that want to go fast. This seems like it might be an ok option if I can get the framer on board and he plans for it.

3) have framers give me a 3/4″ strip of ply at the top plates and tape over may plates onto this. then have them give me 1x strapping on the u/side of trusses and 3/4″ ply strips where each partition will go. Then all my ceiling can mate up with the ply and other than a bit of sealant I’m not asking them to do anything special or out of sequence. Downside here is a decent amount of extra framing material and labor.

4) sheathe the u/side of trusses and tape the joints, strapping over this for the gyp a service chase. Clearly the most involved/expensive.

Any input on the relative merits of the above options?

From talking to framers it’s all about speed – they estimate being framed in about 7 working days, said to assume 2 weeks total to account for weather and surprises. So it seems that anything that slows them down they’ll punish me.

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Replies

  1. Expert Member
    AKOS TOTH | | #1

    I would say option 3 would be the one least likely to be messed up. It is a bit more cost but you also get the benefit of tighter spacing with the strapping for the ceiling which lets you use more blown in insulation in the attic.

    The way I've done air barrier transition from exterior sheathing to interior drywall is by putting a wide strip of flashing tape over the top of the wall. The tape overhangs the outside by about 2", this folds down over your sheathing.

    Similar overhang on the inside but you leave the paper over the tape until the drywall is about to be installed.

    The tape can than be stapled up against the rafters. Remove the paper backing, install the drywall and roll the tape from the attic.

    You can do a similar setup over interior walls.

    This only works if you do the taping yourself, option 3 is something you can get trades to do.

  2. Nat_T | | #2

    Thanks, Akos. That's the option I've been showing so far (#3) but all of the framers were unfamiliar so I was wondering if I should go another route. I may stick with this option as it seems relatively dummy proof as you said.

    Is the problem with #1 that it is not easily/feasible to seal well like this?

    1. Expert Member
      AKOS TOTH | | #6

      It is a lot of liner feet of caulk. I tried this for my home, I found that even with me trying my best to be careful it is just hard to do a consistent job. I had to touch up a bunch of areas down the road where the caulk separated.

  3. Expert Member
    MALCOLM TAYLOR | | #3

    Nat,

    My two cents:

    #1 Would work fine - especially if you have access to the ceiling from above so you can do the odd bit from there too. Another variation I've seen used here is to run gaskets at the lower top plate before any of the drywalling occurs. As long as the boarders are careful doing the ceiling, and don't mess them up.

    #2 Unhappy subs on this option should also include the electricians and plumber who have to rough-in from above travelling through a hatch, rather than work off ladders.

    #3 Does a good job of providing backing at the ceiling, but involves a lot of additional work, and all the strapping still doesn't give you a service cavity to run wiring inside the air-barrier. This option would work a lot better if you could figure out how to include a variable perm membrane on the underside of the trusses.

    #4. Doesn't yield a big en0ugh benefit to justify the work and cost.

  4. Nat_T | | #4

    Thanks, Malcolm.

    By gasket do you mean something like the canned stuff such as "Great Stuff Drywall Gasket" that comes in a can? That seems easy enough to do and would only run a couple of hundred bucks. Or is there some other type of strip gasket that you were referring to?

    The only other upside with the strapping that I saw was more support for the sheetrock to carry the insulation vs the @24 o.c. studs (assuming I strap at 16). But if I use 5/8 gyp i'm not sure it's really necessary.

    1. Expert Member
      MALCOLM TAYLOR | | #7

      Nat,

      No, a foam gasket. One production builder near me just stapled up a sill gasket folded half onto the top plate and half onto the backing above and got good results.

  5. Expert Member
    AKOS TOTH | | #5

    A better option might be to get one of the small 2 part spray foam kits and seal up all your top plates and penetrations once the drywall is up from the attic.

    The kits aren't cheap but since trades don't have to to anything extra, should be lower cost. You can do an entire house in a couple of hours. I find that the fan tips work much better for this type of work, sometimes you have to buy it separate.

    No matter the way you go, it is worth to do a blower door test before things are covered up and fix any big leaks.

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