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Community and Q&A

Sealing Drywall Before Blower Door Test

jvidamins | Posted in General Questions on

Starting my first house with “Pretty Good House” standards more or less. Im actually shooting for Net Zero Ready. 2×6 walls with Rockwool (r-23) and Zip R9, R -60 cellulose in the attic with 20” energy heel trusses. I’ve been reading and researching a lot in the past several months, but I’m having trouble figuring out one thing at the moment. How do you seal the ceiling drywall after rough-ins are complete? I’ll be using something like 10” Zip Flashing Tape to connect the zip R9 up, over, and down the top plate (unless someone can recommend a better solution there – I won’t be using furring strips so using osb is out). Then, I was going to use Great Stuff Flexible Foam Drywall Gasket on the sides of all the top plates prior to installing the interior drywall on the walls…. But until that’s done, won’t there be leaks at every single top plate – interiors and exteriors – causing a terrible ACH50 score? If so, what am I missing? If not, what am I missing? 😂

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  1. user-1116814560 | | #1

    Looking forward to other responses, but am wondering what your climate zone is as well as subslab insulation will be like as well as your window package…thats a pretty aggressive wall and ceiling package, will these other two important elements be consistent?

    1. jvidamins | | #2

      Ah yes… good question. R-10 rigid foam sub slab, r-5 rigid foam on interior of 9’ foundation walls, with 2x4 framed walls with Rockwool batts. I’m in north central Indiana, climate zone 5. I’m in the process of choosing windows now, but I’m guessing they’ll just be double pane.

      1. jvidamins | | #54

        Actually went with Triple Pane windows with a U-factor of .18, for what it's worth...

  2. Expert Member
    DCcontrarian | | #3

    The guy who did my blower door wanted to do it after drywall and before painting.

  3. DavidDrake | | #4

    Had the same issue. It didn't help that I screwed up and neglected to provide a means to continue the air barrier from the sheathing to the drywall ceiling before I set the trusses on the top plate.

    Basically what I did was temporarily tape the edge of the drywall to the top plate for the blower door test. That plus fixing a few other spots revealed by the fog machine left the ceiling airtight. Improvement from before and after taping was pretty dramatic. I'm reasonably convinced with the rest of the interior drywall hung, and temporary tape replaced with caulk, and drywall tape and mud, I should be able to hit a goal of ≤1 ach50.

  4. Randy_Williams | | #5

    My climate is a little different than yours, but this is how I handle an inexpensive air seal for an unconditioned/vented attic.

    You can substitute the poly with Certainteed's Membrane or one of the other variable perm products such as Intello or Majrex. Factory built trusses are common in my market. I try to design my projects so that the truss can be set before any interior walls are built, that way the air control is continuous. Drywall can also be used, but mechanical/electrical/plumbing systems will need to be thought through. Are they installed before the drywall or does someone crawl around the attic after? The latter results in very unhappy subs. If I have ductwork located in the ceiling, my preference is to use a plenum truss.

    My last blower door test when using the system outlined in the article resulted in a .38ACH50.

    One piece of advice, if you decide to use Intello for the ceiling, be aware that tape does not stick well to the backside of that membrane. With the tape run over the top plate, this is where that connection is usually made.

    1. jvidamins | | #11

      I'd prefer to just use the drywall at the ceiling to save on costs. Just trying to figure out how to seal the top plates. Every article I read says, "Just have rough-ins done, hang your drywall on the ceiling, then you're ready for the blower door test" without addressing the obvious top plate gaps you'll have at that stage. I figured I was just missing something because it seems you'd fail if that's all you did.

  5. Expert Member
    BILL WICHERS | | #6

    I think you have your blower test scheduled too early in the construction process. Normally blower door testing is done pretty late in the construction process, after all the air barrier stuff has been installed -- remember that blower door testing is intended to test the effectiveness of air barriers after all :-) Since drywall normally acts as the primary air barrier, it really needs to be in place prior to blower door testing. The usual "seal" on the drywall would then be the normal mud and tape work at the joints. You don't want to cover anything with an extra air barrier, since that will give you a false blower door test result, since the blower door test is testing the temporary air barriers and not the final home as constructed, which is what the test is supposed to be testing.

    I recommend you reschedule your blower door test until rough finishes are in, which would include all drywall being up, taped and mudded, and other basic sealing operations being complete.


    1. jvidamins | | #9

      From what I read, the ideal time for the blower door test, at least the initial "air barrier check" one, is once the air barrier is complete, but before exterior wall insulation and drywall, since you can't easily correct any gaps once those are up. Since my ceiling air barrier is going to be drywall, my plan was to have plumbing, eletrical, HVAC all roughed in, then install the ceiling drywall. That's what all the articles say to do... but my question is how is the ceiling air barrier truly complete at that point, without the drywall being installed on all the walls, which will seal up against my Great Stuff Flexible Foam Drywall Gasket on the sides of all the top plates? It sounds like the only way would be to not use the gasket method, but rather seal it with closed cell spray foam from the top, which would be a lot more expensive. Or just not use the drywall as my ceiling vapor barrier, but rather something like what @Northernbuilt suggested (poly or a vapor open Intello or Majrex).

      1. Expert Member
        BILL WICHERS | | #22

        It really depends on what you are testing with the blower door. If your primary air barrier is the exterior sheathing (or exterior rigid foam, anything on the exterior instead of interior drywall, basically), then it makes sense to run a blower door test to test that air barrier prior to closing things off with interior drywall so that you can't fix the "other" air barrier as easily. If you have no ceiling, then you'd need a temporary aair barrier. If you are doing a hybrid assembly, where the exterior sheathing on the walls is the primary air barrier in that location, but the ceiling drywall is the air barrier "on top", then I'd use house wrap or polyethylene sheet -- something cheap -- and tape it to the top of the primary air barrier for the test. You'd then run a second blower door test when the ceiling drywall went up so that you'd be testing the finished assembly. This would be a sort of "phase 1" for the exterior air barrier and a "phase 2" for the ceiling drywall air barrier.

        If you do two tests, you don't have to worry about your drywall gasket, since it will still work when you put up that drywall for your second blower door test. It really comes down to what you want to test and when, and a drawing might help to show any specific details you're asking about around the top plate.


  6. DavidDrake | | #7

    Probably should have clarified why I did a first blower door test when I did. My primary air barrier is the sheathing and the drywall ceiling. Because I'm doing nearly all the work myself, and because this is the first time I've attempted a reasonably well-sealed building, I wanted to test while the stud bays were open and uninsulated so I could locate and fix problems between the sheathing and the framing. Good thing I did, since there were significant leaks into the attic where I'd added framing on the interior side of the gable end trusses. I thought I'd sealed them, but the blower door and fog machine made it obvious I need to do a better job. Those leaks would have been impossible to fix if I'd already insulated and finished the walls.

    In other words, I used tape to temporarily seal the ceiling to top plate, so I could find leaks in the permanent air barrier at sheathing, and in areas of the ceiling other than the perimeter (such as electrical box penetrations). Since that test, I've dense packed the walls and started hanging drywall on the wall. After taping and mudding, I'll do another blower door test.

    I assumed the OP had a similar strategy in mind.

    Of course, doing DIY project, I have the 'luxury' of being able to do some things out of sequence, and correct some mistakes without a cash penalty (just my time). Which is probably why I'm still not finished :).

    1. Expert Member
      BILL WICHERS | | #8

      If that's the case, and this is a sort of "phase 1" blower door test to verify one part of the assembly prior to closing things up more, then I'd probably use either poly or house wrap for the temporary air barrier. You would want something cheap and easy to put up, which means something like those two products. Tape and a staple gun would work for a temporary "installation".

      Blower doors don't really run particularly high pressure levels, so regular tape should hold OK as long as it has enough overlap with whatever it is being stuck to. Just try to put the sheet on the right side of the open framing so that the pressure of the blower door pushes the sheet against the framing and not away from it. With the sheet pressing againt the framing, the framing helps take a lot of the load so that the tape doesn't have to. If the entire thing inflates like a big balloon, bowing out from the framing and not pressing against it, the tape will have a much more difficult job and will probably fail.


    2. jvidamins | | #10

      You taped the ceiling drywall to the top plates? What tape did you use for this? That seams like a lot of work... (see what I did there)

  7. jvidamins | | #12

    Thinking this through a little more... wouldn't it be ok to go ahead and install my rockwool in my 2x6 walls and drywall/tape it there right along with the ceilings, just like a normal build? Since my exterior wall air barrier is on the outside via Zip R9 sheathing, if there is any leak, wouldn't the fix have to be done on the outside of the zip anyway? I guess, would there really be a benefit of not having the walls insulated and rocked in this case? If I use the pressurize/fog machine method to find my air leaks, will the fog still be able to go through the air gaps in the exterior walls if they're rocked and insulated?

    1. jvidamins | | #13

      Anybody have any thoughts on the above?

      1. Expert Member
        DCcontrarian | | #16

        Are you asking if the insulation will block the fog but not the air leak? Probably a question for the blower door operator.

  8. Expert Member
    Akos | | #14

    The issue with fully finished interior walls is that you can't see the leaks. You know they are there but because all those cavities, the airflow you see might be far away from the actual leak source.

    I think the simplest in your case is to use a membrane for the ceiling air barrier. 6mil poly has been used for a long time for this, unless you are in warm climate, there is nothing wrong with including poly in the ceiling with a standard vented roof. You can always substitute the poly for one of the fancier membranes or 1/2" plyiso.

    This lets you do a blower door test early enough to spot problems while keeping the build to standard workflow and moving along.

    1. jvidamins | | #15

      If all the drywall was finished and there was fog coming up through a hole in the attic, wouldn’t you just find the seam/hole and seal it from the attic with closed cell foam? Similarly, if you saw fog coming out from between 2 sheets of zip or from the sill/foundation connection, wouldn’t you just need to apply more flashing tape/caulk at the exterior? Would it matter where the air is coming through at the interior or exterior sheetrocked walls, since that’s not my air barrier anyway?

  9. Expert Member
    DCcontrarian | | #17

    I think you're asking the wrong question. You've stated that you want the exterior sheathing to be your air barrier everywhere but the ceiling, where you want it to be drywall. The air barrier needs to be continuous. So the question isn't how to tie the drywall to the sheathing for the blower door test, it's how to tie them together period.

    Is your plan to run the Zip tape over the top plate before rafters and ceiling joists? One thought would be to cut the backing tape so that 2" of the backing tape remains, and stapling that to the underside of the joists. When it's time to drywall the ceiling remove the backing and put the drywall into the exposed tape. You'll probably have to go into the attic and press the tape down.

    1. jvidamins | | #18

      Correct. I’m planning on Zip taping over the top plate to connect the sheathing to the ceiling. I see what you’re saying, but all the interior walls (which wouldn’t yet have drywall either) would all be leaking at the interior wall top plates, so I couldn’t do the blower door test at that point. I was asking, if I went ahead and applied the Great Stuff Flexible Foam Drywall Gasket on the sides of all the top plates, then installed all the interior and exterior wall sheetrock (at which point I would have a fully sealed air barrier) could I then run the blower door to pressurize the house and use the fog machine to find any leaks in my air barrier? If there are leaks in the exterior walls, I could see them from the outside still and seal them up, right? Same for the attic space…

    2. DavidDrake | | #21

      "So the question isn't how to tie the drywall to the sheathing for the blower door test, it's how to tie them together period."

      This is very good advice for the OP, I think. I wound up using a makeshift solution for my initial diagnostic blower door test because I neglected to provide a better method for tying the sheathing to the ceiling. That mistake forced me to rely on an airtight caulked/foamed connection between sheathing and top plate, top plate and wall drywall, and wall drywall and ceiling drywall.

      I taped the ceiling drywall to the top plate to isolate any air leaks in the sheathing and in the ceiling penetrations so I could fix them before insulating the attic and bays. This was a work around—not ideal.

      Connecting sheathing to top plate to ceiling drywall with a membrane or Zip tape or similar before the trusses were set would have been much simpler. I simply didn't think to do it until it was too late.

      I'm sure there's a few folks who can get these things right on the first go. For me, even after a few years of research, designing, and asking questions on this site, I still made plenty of (in hindsight) obvious mistakes. There's just an awful lot to know, even for a modest project.

      Fortunately, I think I learned enough from GBA and other sources that none of my mistakes have been catastrophic. My ACH50 number likely won't be braggable, and there's plenty I'll change on the next build, but I think I'll still wind up with a net zero building, well-designed comfortable spaces, and a solid return on investment (as long as I don't count my labor :-).

      1. jvidamins | | #25

        Yes, I’m using Zip tape to tie in at exterior top plate. And I’m wanting to use the Great Stuff or similar foam gasket to seal the interior top plates to the drywall. I’m just trying to find out if I can insulate my exterior walls with Rockwool, then install all the sheetrock (walls and ceilings), then run my blower door test with the fog machine.

        I know I’ll have a complete and connected air barrier at this point… I’m just asking if the fog machine will still work to locate air leaks at the exterior walls.

  10. thrifttrust | | #19

    I was presented with the same issue on the gut remodel I'm currently working on. Like you I made the sheathing air tight and sealed it to the top plate. Then I simply installed the ceiling drywall as usual. As I installed the wall drywall I first applied a bead of sealant (Green Glue Sealant) to the top plate. Now the ceiling is automatically made airtight through the normal drywall taping process. My blower door test came in at .77 ACH.

    Don't forget, all interior walls have the potential of leaking air into the attic. I sealed all interior wall drywall to their respective top plates just like the exterior walls.

    Douglas Higden

    1. jvidamins | | #24

      Yes, that’s very similar to what I’d like to do. See my latest comment below… Did you do a fog machine test to try and spot leaks with your blower door after you did all of that? Did it still work with the drywall and exterior wall insulation up everywhere?

  11. Jeremiah_Sommer | | #20

    Are you required to install any sort of vapour control layer between your drywall and trusses? Or is your drywall/latex paint acting as both vapour and air control?

    It sounds like you are looking for a way to create a seal at the ceiling so that a pre insulation/drywall blower door can be performed. I’ve never installed drywall as a primary AB as you are suggesting however getting this detail correct would require that you install all of your ceiling drywall prior to framing your interior walls. That way you only have to seal around the perimeter of your exterior walls. Definitely takes some sequencing to make sure your wiring/plumbing penetrations are accounted for.

    I have always found that installing a membrane like poly or Intello with taped seams service cavity furring below to be the simplest. Requires more material but then your drywall can just be drywall.

    1. jvidamins | | #23

      No, I’m not required to install a vapor barrier at trusses, other than drywall/paint, which is my intention. I’d rather not go the extra expense adding something like Intella (it would add at least another $3,000) when the drywall/paint is already going to be there serving the same exact purpose.

      I also don’t think I’ll be installing the ceiling sheetrock prior to interior wall framing. I’m trying to make the build as normal as possible for me and my framers (this is my first Net Zero Ready home).

      My plan is to tie in my exterior Zip R9 to the ceiling drywall by taping the exterior top plate prior to setting trusses. Then once all the interior walls are framed, I was going to install just the ceiling drywall, then run the first blower door test. But I now realize I would have way too many ceiling leaks since there would be nothing stopping airflow into the attic at the interior top plates. At this point, I could air seal the top plates from the attic using closed cell foam, then I’d be tight and ready for the blower door test - but I’d rather not do that as I think there must be a cheaper option. So my thought process was, well, I could just go ahead and insulate the exterior walls and sheetrock ALL the walls using the foam gasket at the interior top plate method to seal up the interior top plates from air leaks. Of course all the rough-ins will be in already at this point like normal. So my question now becomes, if I do this, can I now run the blower door test with fog machine to test for breaks in my air barrier? Mind you, there is NO insulation in the attic yet - only the exterior walls. If I had an air leak somewhere on my Zip R9 exterior air barrier, I’d still see the fog coming outside through the drywall/Rockwool, right? If so, then I can easily seal it from the outside. Similarly, if I see fog in the attic, I can seal it from the attic with closed cell foam.

      Does anyone see a problem doing it this way? It really sounds like it would be A.)the most cost effective solution, and B.)the most traditional solution for my subs

      1. DavidDrake | | #45

        "I’d rather not go the extra expense adding something like Intella (it would add at least another $3,000) when the drywall/paint is already going to be there serving the same exact purpose."

        Wow. Does that include labor? Because the material cost I'm seeing for Intello is around $0.50/SF ($776 for 1614 SF Intello X Double-Wide), plus about $40 for 100' of Vana tape.

        I went the drywall route as well, but would consider Intello on a future build if cost is reasonable vs. ease of installation.

  12. Jeremiah_Sommer | | #26

    I totally get your desire to simplify the process for subs. I also understand that you would like to omit furring on the ceiling, however this is typically an inexpensive and straightforward detail that framers should be able to execute. By using 3/4" furring you could also use Zip sheathing over your top plates so that your drywall to ceiling connection could be sealed as you install (see sketch). You would still need to seal other penetrations accordingly but this may work as a buildable option for your subs.

  13. Expert Member
    DCcontrarian | | #27

    I still think that you want to tie the exterior walls to the ceiling and not the interior walls.

    Here's a suggestion: you can buy Tyvek in 3' rolls. Run a strip of 3' Tyvek over the top of the exterior walls with 6" hanging down on the exterior and 24" hanging down on the interior. Staple and tape on the exterior and top plate, but leave it loose on the interior. Once the trusses or joists are placed, staple the Tyvek to the bottom of the joists. Then use the drywall gasket compound on the ceiling between the ceiling drywall and the Tyvek. You'll probably still need to tape the Tyvek to the drywall in the attic, but since you left yourself 24" you don't have to go into a tight corner to get to it.

    If you're not doing ceiling drywall before interior partitions, do the same thing at interior partitions. Otherwise you have to make sure your interior walls are sealed, because they provide another path to the attic, and that's a lot more surface area to seal.

    I believe this costs less and is less work than what you're proposing with Zip tape. It also works better.

    1. Expert Member
      DCcontrarian | | #28

      Basically you could take J's diagram from post #26 and substitute Tyvek for OSB.

    2. jvidamins | | #31

      I wouldn’t be using zip tape on interior partitions. I would be using Great Stuff Flexible Foam Drywall Gasket on the sides of all the interior top plates. Once the Sheetrock is hung on the walls, it compresses that gasket and seals off the top plates from air leaking through the interior walls via electrical switches, outlets, etc. It seems like the simplest way to complete this seal. If any leaks are found in the attic while doing the fog/blower door test, I’ll just seal it from the attic with some closed cell foam. Also, I believe this same gasket product applied to zip tape which is coming up/over/down the exterior top plate, will act as the ceiling to exterior air barrier connection.

      1. Expert Member
        Akos | | #32

        You want to seal the ceiling not the walls. This means if you want to use a drywall gasket you need a flat surface to seal against. This can be done if you strap out the ceiling and have a strip of 3/4" OSB over the wall top plate that overhangs the interior and exterior walls.

        What I have done is use the same idea as for the exterior walls for any interior partition. Instead of a wide piece of tape, what works better is two narrow ones with a split release seam. This way half the tape can adhere to the top plate and half overhang with the backing in place. Once the walls are all framed up, the backing is removed and the air barrier (6 mil poly) is adhered to these pieces of tape.

        Installing the ceiling air barrier is the last step after all the electrical havc and plumbing is in. Once the ceiling air barrier is up, the place is ready for blower test before any insulation on drywall goes in.

        This only needs a couple of extra steps to install the tape during framing and it follows standard workflow.

        Instead of smoke machine, it is much easier to find air leaks if there is a temperature delta between indoors and outdoors. Not an issue for a good part of the year up here in the great white north. I have a heater that connects to a stove plug that puts out about 20kBTU/h, it does a decent job of getting a reasonable sized place up to temp. Once it is warm inside, pull the place to negative pressure and look around with a thermal camera. Even small leaks are visible right away and can be sealed before any drywall goes up.

        After all this, install the drywall in an air tight manner to help seal the place even better.

        1. jvidamins | | #35

          I have read many places that say you can effectively seal up the inner wall cavity air from leaking up into the attic by sealing the wall Sheetrock at the side of the top plates using the spray foam gaskets guns. I believe this, along with drywall portion above the gasket, then tape/mud at the corner, also allows the red pen not to lift from exterior zip to the ceiling. Unless I’m missing something…

  14. user-1116814560 | | #29

    The assumption is airtight drywall will still be vapor permeable right? Is that assumption still true is using 5/8 drywall in ceiling?

    1. Expert Member
      DCcontrarian | | #30

      Half inch drywall is about 50 perms. If the vapor resistance is in the gypsum you'd expect 5/8" to be 40 perms. If it's in the paper you'd expect no difference.

      In either case the permeability of the primer and paint is going to be the defining factor.

  15. user-5946022 | | #33

    I have not read all of the response, but I think you are on the right track to test at the stage you want to test...I say this as the occupant of a house where the drywall basically functions as the air barrier. That is great for the day of the blower door test.

    HOWEVER - every time I hang a photo, or the electrician cut the gyp because he lost a box, or the radon guy cuts the gyp to install the manometer, or...or....or. There are so many times in normal occupancy and finishing of a home that the gyp may get cut and having it as the main air barrier is nerve racking. I soooooo wish I had insisted on air sealing with blower door testing BEFORE insulation, and the wall gyp were the secondary air barrier. Having the ceiling gyp be the primary air barrier is not such a big deal as there are far fewer times ceiling penetrations are made.

    There are two main approaches:
    1. Hang the ceiling gyp before the wall gyp, and air seal the gap at the edge of the gyp to the plates by spraying a bead of canned foam from the attic. Any that expands down you can easily trim before hanging the wall gyp. Contractors do not want to do this because it causes the gyp crew to have to come out twice, which is somehow far more objectionable than the insulation crew having to show up twice. I get this, because the guys hanging gyp make a mess, so there are two messes to clean up, etc. and the wall insulation crew is probably different than the blown in ceiling insulation crew. If doing it over I would still pay for this though.... and if you are hanging the gyp yourself definitely do this.

    2. Hang something like intello onto the underside of the trusses and have that be your air barrier. Staple it to the top of the inside corners then tape it to the top plate.

    1. jvidamins | | #34

      Holes in interior/exterior Sheetrock does not affect air barrier, unless your using the “airtight drywall” approach as your sole air barrier. My exterior wall air barrier is not the drywall - it’s the Zip R9 sheathing on the outside of the exterior wall.

      1. user-5946022 | | #39

        I believe you may have misunderstood my post
        - You asked about blower door testing before gyp, indicating you intend your air barrier to be the exterior sheathing at the vertical walls, and the gyp at the ceilings.
        - I replied that as the owner of a house in which the drywall basically functions as the air barrier because the house was NOT tested without drywall, I encourage you to do all you can to get your blower door test to the number you want before the vertical wall interior gyp is installed. That will help ensure your house is tight before the gyp. Otherwise you will never know, and every hole in the gyp MAY impact your air barrier, even if the gyp is not your sole air barrier.....that hole in the gyp might just be exactly where the gap in the exterior sheathing air barrier is - if you don't test before gyp you will never know and your chances of catching those leaks in the sheathing dramatically decrease...

        1. jvidamins | | #41

          I hear you, but how can a hole in the gyp be where the gap in the exterior sheathing air barrier is?? The performance of the zip as the air barrier has nothing to do with the drywall inside. I don’t plan on doing any “airtight drywall” practices on the exterior wall, so there will be all kinds of “holes” there. I don’t care because that not my air barrier - the Zip is. If there’s a leak somewhere in the Zip, then I’ll tape the Zip with more flashing tape and that will be that. I’m not planning on installing siding yet, so I can still view leaks in my Zip and fix them at the intitial blower door test, even if the drywall is up. I just hope the fog machine will still work to show me any gaps.

          1. user-5946022 | | #46

            I believe you have misunderstood my post.
            - You asked about blower door testing before gyp, indicating you intend your air barrier to be the exterior sheathing at the vertical walls, and the gyp at the ceilings. You asked how to seal at the inevitable gap between the ceiling drywall and the top plates, prior to the vertical wall drywall being installed.
            - I replied that as the owner of a house in which the drywall basically functions as the air barrier because the house was NOT tested without drywall, I encourage you to do all you can to get your blower door test to the number you want before the vertical wall interior gyp is installed. This is also what you posted you are intending to do. I then further answered your question with "Hang the ceiling gyp before the wall gyp, and air seal the gap at the edge of the gyp to the plates by spraying a bead of canned foam from the attic."

            This should address your concern about getting your house as airtight as possible before wall gyp. You should then also attempt to create a secondary air barrier with your wall gyp, as a good practice, and to further increase the tightness of your house, because it is cheap & simple. But you don't want to, fine.

            To answer your follow up question of "how can a hole in the gyp be where the gap in the exterior sheathing air barrier is?? " because you might have an exterior electrical box roughed into the same stud bay that an interior electrical box is roughed into, and either the electricians who finish your house, or an electrician who works on it in 75 years when you are long gone may defeat whatever air sealing measures you took at the box, so there is now an air leak in that stud bay.

  16. jvidamins | | #36

    For everyone saying the gasket has to be touching the ceiling drywall… see the attached. Is this detail incorrect then?

    1. jvidamins | | #37

      Here’s another picture from an article written by Martin stating to use the gasket between the wall Sheetrock and the side of the top plate…

  17. jvidamins | | #38

    Here’s another from Building Science Corp…

    1. user-5946022 | | #40

      @jvidamins - everyone is saying to install the gasket to the side of the top plate because in most typical construction that is the only continuous surface - there is no continuous surface on the ceiling. So you install the gasket to the continuous surface, and then tape the wall and ceiling gyp inside corner and you have an air barrier.

      That is why I suggested instead of messing with the gasket, install your gyp, tape & bed the abutting seams, then get some canned foam or even better a froth kit, and go in the attic and spray the perimeter of every room. This will get you a decent air barrier.

      There are also other ways, which include taped membranes to which gyp will be applied later, or installing a piece of plywood at the perimeter to get yourself that horizontal continuous surface onto which you can install a gasket.

      1. jvidamins | | #42

        I was originally going to do that (seal the top plates from the attic with closed cell foam) but that’ll be more expensive, and harder, than the gasket approach (in my mind anyways… lol) I was going to save the closed cell from the top method to seal any leaks still there after the drywall is hung, before the R-60 is blown in the attic, at which point I hope to never see the top plates again.

        1. user-5946022 | | #47

          Why don't you try hanging a small room of ceiling gyp using your gasket approach to determine if you think that is easier than hitting the perimeter of the room from above with spray foam (either from a can or a froth kit).

          1. jvidamins | | #49

            Because I'm not hanging the sheetrock. My sub will come in and would like to do the entire house all at once. With the foam gasket method, I'll do that around the top plates the day before they come in and that's that. If there are any air leaks into the attic while doing blower door/fog, I'll seal those with closed cell foam from the attic.

    2. Expert Member
      DCcontrarian | | #50

      In that one the drywall is definitely the wall air barrier. In the two earlier ones it's hard to say but no wall air barrier is shown.

  18. thrifttrust | | #43

    I like that you found those articles. The resistance to drywall used as an air barrier baffles me. It's about the only air barrier that is always available for inspection and repair. The wall is sealed to the top plate and drywall tape perfectly seals to the ceiling. With a simple bead of sealant to ALL top plates you've guaranteed that little air will escape to the attic. One disadvantage is that it doesn't work until the drywall is up, but with careful exterior sealing you shouldn't have to worry. However, with a little more sealant and airtight electrical work, per the Building Science Corporation article, you can make your wall drywall a secondary air barrier. I think using the DOW drywall gasket foam would make the process easier and less prone to drywall installation error. However, a good method to prevent smearing the sealant bead is to screw a couple wood blocks to studs 48 1/4 inches from the ceiling, then rest the drywall on the blocks and pivot it toward the top plate. It's a good idea to do a test fitting before applying the sealant bead.

    1. jvidamins | | #44

      Awesome! Thanks for affirming my assumptions! :) I believe I'm going to go this route as it just seems the easiest by far... I just hope the fog will be able to make it through any leaks in the exterior assembly once it's rockwool'd and sheetrock'd. I'm sure it will... just haven't done this before so wanted some reassurance that I'm ok to do the "air barrier" blower door test at this point. Since I'll still have the ability to seal any holes via outside and in the attic, I'm hoping it'll be fine.

    2. Expert Member
      DCcontrarian | | #51

      There's no resistance to using drywall as an air barrier. The resistance is to using interior drywall along the top plate to bridge the union between a ceiling air barrier that is drywall and a wall air barrier that is the sheathing.

  19. user-5946022 | | #48

    "I just hope the fog will be able to make it through any leaks in the exterior assembly once it's rockwool'd and sheetrock'd."
    It won't. The gyp is a secondary (or when testing from the inside, primary) air barrier, and if it is working you won't get air leaks at that initial test.
    You will however get air leaks after you side, move in, and begin living there, hanging pictures, making changes, etc.
    Test before installing wall gyp.

    1. Expert Member
      DCcontrarian | | #52

      He wants to test before installing the wall gyp. However, he also wants to use part of the wall gyp as an air barrier. Something has to give.

      1. user-5946022 | | #53

        Yeah. Then he says the gyp sub wants to hang the ceiling & wall boards all at once. I imagine that subs finisher also wants to finish the ceilings & wall all at once. So he won't get an opportunity to test with just the ceiling gyp....

        People go to all sorts of lengths to install a separate air barrier on the ceiling. The material & labor costs for that seem to far exceed whatever the cost is to just pay the gyp sub for one extra mobilization.... and you can also then save by paying the insulation sub for only one mobilization.

  20. jvidamins | | #55

    Sorry to resurrect this thread but I'm about a week away from setting trusses and wanted to see what you all thought of this plan...

    Use 3M 8067 12" flashing tape to attach to exterior Zip R9 2" down, then over top plate/zip (7.5"), leaving 2.5" hanging over inside with the backing still on the tape. Then once trusses are set, staple the tape to the bottom chords of trusses, but leave the backing on still. Then a day or 2 before drywall, come in and apply great stuff pro flexible foam drywall gasket to all the INTERIOR wall top plates. Then, have the drywall hangers ONLY install the ceiling (removing the backing of the 3M tape first of course) and interior walls (creating that interior wall top plate air seal), but NOT hang the exterior wall drywall yet. I spoke to my dry waller and he said that's not a problem. Then, have my drywall finisher come in and finish the ceiling and interior walls. If I'm not mistaken, this should complete my air barrier envelope so that I can do a blower door test and use the fog machine to check for leaks. Once any holes are located and buttoned up, I can then install exterior wall insulation and have the dry wallers come back to hang and finish the exterior walls.

    Am I missing anything? Does this sound feasible?

    1. scottohara | | #56

      I build Net-Zero spec houses and my process is more like what @thrifttrust does in post #19 and it's worked well to get to the .95 ACH without stopping to test and check with fog before installing the wall drywall. I've not been willing to send the drywall guys away once they're on the job.

      Have you tried to peal the backing off of the 3M tape after it has staples through it? It seems like it could leave pieces of backing that the drywall guys most likely aren't going to take the time to address. It also seems like someone would need to be on top rubbing the tape to make sure it's thoroughly adhering.

      I may have missed something but are you planning on taping the seams in the drywall and sealing the penetrations before you test?

      It sounds like you're going to have some days between the ceiling and wall drywall installations. You may want to hold off on the Great Stuff until after the ceiling is installed to put it on. It will prevent it from being damaged when they're lifting the ceiling sheets.

  21. jvidamins | | #57

    I'd probably be the one to take the backing off the tape the morning of drywall install day, just to make sure it's adequately done. I'm hoping it'll stay sticky while they're cutting drywall and the drywall dust isn't going somehow stick to it and cause the 3M not to stick anymore. After the ceiling is installed I was planning on rolling it from the attic.

    Yes, the seams would be taped and finished prior to blower door testing.

    Not positive on the timing of the install. It's 2,600 SF on the main level and 2,150 SF finished in the basement (of which they can hang both ceiling and walls down there). I'm guessing it'll take them 2 days to do all of it?? They have a pretty good sized crew. I'll have to double check to make sure they can just do main level ceiling and entire basement on day 1 (so I can apply the gasket to the interior top plates after the ceiling is up), then come back on day 2 to hang interior walls on main level. He definitely didn't have a problem coming back at a different time to install the exterior walls, though.

    Side question... do you apply that gasket to the bottom top plate, or the top (double top plate) or does it not even matter?

    Maybe I'm overthinking this, but since this is my very first Net-Zero Ready home, or anything even in the same ballpark, I'd like to get that verification that the air barrier was actually done correctly and I didn't miss something big before it's all buttoned up and inaccessible.

    I haven't heard of anyone approaching it this way though (leaving exterior wall drywall hanging/finishing for later) to be able to test their air barrier. I've only heard of not drywalling anything and just using something like Intello or something on the ceiling... so just want to make sure this will work.

    1. Expert Member
      Akos | | #58

      You'll need to add blocking between the trusses or rafters beside the wall top plates for the tape to sit against. The blocking can be fastened to the top plate, this is especially important with interior walls where you want to decouple for truss lift.

      I've only done this with 6mil poly as the air barrier in which case you can roll the joint to seal it. If you want to use drywall only I think the simpler is to stick a foam gasket to the tape. Once the drywall is screwed in place, it will compress the gasket for the air seal. Maybe one of the standard drywall gaskets will work for this (ie BG32) or one of the foam sill gaskets.

      Make sure the drywall crew fastens at the perimeter to compress the gasket.

      P.S. You don't want the rest of the ceiling in (main and basement) so you can find and fix any leaks in the rim joist area.

      1. jvidamins | | #60

        I spoke to my framer about this and he actually said he thought the 12" tape with the split backing would be too hard to handle and implement and actually like my 2nd option, which was OSB/Advantech on the top plate overhanging 2 1/2", to which I'd just apply Great Stuff Drywall Gasket to the bottom of for the the drywall ceiling to mash up against. We'd then have to use 3/4" strapping/furring strips 16 oc. But then the interior wall top plates would also need the same OSB/Advantech treatment, right? Maybe an 8" strip so it would overhang each side of the wall by 2 1/4"? That would also be a great solution to prevent truss lift, right? Maybe this will kill two birds with one stone. Thoughts?

        1. jvidamins | | #61

          FYI... this is what I ended up doing.

          1. Expert Member
            DCcontrarian | | #62

            Have you done the blower door? How did it work out?

    2. scottohara | | #59

      I hope it goes smoothly. It will be a good test and learning experience for you.

      The gasket goes on the top, top plate. If you ever do BIBS in the exterior walls make sure they staple the netting to the bottom, top plate and cut the netting off between the two plates giving you room for gasket above.

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