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Whether to seal where drywall doesn’t reach the bottom plate

gfranke | Posted in General Questions on

The drywall just went up in my house reconstruction project (zone 4A) and there are places where the drywall doesn’t reach the bottom plate, exposing a small section of blown-in cellulose in the stud bay (see attached photo).

The contractor says that is normal, it will be covered up by the baseboard and the wood flooring, and the baseboard will be caulked to the wall. That may help a lot, but to me it seems a lot like to having a large bay of unsealed electrical outlets.

Around 80% of the sheathing joints are taped, so there is a pretty good air barrier at the sheathing layer.

1. Should I try to do something to seal these gaps before the flooring and trim go in?

2. If so, is there a preferred way to do so? The drywall is 1/2 inch, my thought was that if I need to seal them I might take some leftover 1/2 inch ISO boards, cut them to fit in the gaps, tack them to the bottom plate, and run acoustic sealant around the edges.

3. While I am on the topic, would it be worth the time and effort to also apply acoustic sealant where the drywall does meet the bottom plates? I don’t have a lot of time to spare but if that would be very valuable I might try to fit it in.

Thanks.

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Gordon,

    A bit more context will make any replies you get a lot more useful. What air-sealing strategy did you use? Is the drywall the air-barrier for the house, or is there a vapour retarder or membrane as well?

    Not wanting to jump on your contractor, but the industry standard here is not more than 1/2" of gap from the subfloor to the lower edge of the drywall sheets.

  2. Jon_R | | #2

    You could probably fix with flashing tape (that would get covered by baseboard). Generally, I think it would be more productive and efficient to hold builders to some pre-determined blower door result (better than code min).

  3. gfranke | | #3

    Thank you for the questions. The main air-sealing strategy was taping at the sheathing. 3M all-weather flashing tape on the sheathing seams, and Wigluv between the CMU crawlspace wall to rim-joist junction. The reason the tape coverage is not 100% was because I got the carpenters on-board with applying the tape part way through the project and was not able to get back to every single seam that had been missed.

    There is no vapour retarder or membrane and we did not intend for the drywall to be the primary air barrier, mainly because taping the outside seemed easier to either do or convince the tradesmen to do. But I figured I would still seal the electrical outlets and add on whatever drywall sealing techniques I could manage.

    Although the sheathing is mostly sealed with tape the weak point in the house is probably the second floor ceiling, since there is no membrane and the attic space is ventilated.

    1. Expert Member
      MALCOLM TAYLOR | | #4

      If the drywall isn't the main air-barrier things aren't that seri0us. I wouldn't use acoustical caulking on the interior of a house unless it was sandwiched between poly and framing. It stays soft and gets on everything.

      My own preference would be to screw a 2" strip of drywall or plywood to the open sections and caulk the top and bottom. That would be fairly quick and make trim work a lot easier.

      i wonder how your contractor is planning to lay the baseboards with no backing?

    2. Jon_R | | #9

      > taping the outside seemed easier

      But keep in mind that they are not equivalent in terms of moisture performance. So you are doing the right thing by sealing both sides.

  4. gfranke | | #5

    Thanks for the idea Jon. I have leftover 3M tape I can experiment with. I wonder if it will stick well enough to drywall and OSB subfloor.

    We're trying to get through the project with a limited budget and with the normal local contractor/trades guys so I'm not sure adding a blower door clause would have been straightforward.

    1. Jon_R | | #10

      > I wonder if it will stick well enough to drywall and OSB subfloor.
      If not, I'll bet that it would with primer.

    2. STEPHEN SHEEHY | | #21

      We used a lot of 3M flashing tape and it sticks to everything we've ever tried it on. As Jon suggests, try a section and if it doesn't stick, try a primer.

  5. gfranke | | #6

    "i wonder how your contractor is planning to lay the baseboards with no backing?"

    I had that same concern. Isn't the baseboard going to deform if I kick it? The contractor said that with the height of the solid wood flooring the baseboards are tall enough to have plenty of drywall to attach them through.

    1. Expert Member
      MALCOLM TAYLOR | | #7

      Well good luck to him. Trim is typically fastened to the bottom plate and then only sporadically to the studs as needed to keep the top tight. With a factory recessed-edge on the drywall above, and even with wood flooring a gap of 1 1/2", he must be a better finisher than me.

      1. Expert Member
        BILL WICHERS | | #8

        I think this is a “the drywall guy” isn’t the “drywall finisher” and neither of them thought about “the finish carpenter” and it’s probably the finish carpenter that will get stuck dealing with backing for the trim.

        Classic one trade not doing something simple and quick that would save the next trade in line huge amounts of headache and time. I see this kind of thing on projects all the time, unfortunately.

        Bill

  6. GBA Editor
    Martin Holladay | | #11

    Gordon,
    This is an error by the drywall contractor, and is unacceptable, for two important reasons: the integrity of the air barrier, and the need for solid backing behind the baseboard.

    You've gotten a few good suggestions for what to do now. Good luck.

    This story is a good example of why builders who are focused on energy efficiency need to have a pre-construction meeting with all of the subcontractors. At this meeting, you can discuss airtightness goals and the important principles that all subs need to understand. If a subcontractor doesn't know about air barriers, you get the kind of blunder you're discussing here.

    1. Expert Member
      BILL WICHERS | | #12

      I have always advocated weekly construction meetings with a representative from each trade and the owner to discuss any issues that have come up during the week. I find this helps to limit how many small issues become large issues later on the job. Communication between all the trades is important and tends to be lacking on many jobsites.

      Bill

    2. Expert Member
      MALCOLM TAYLOR | | #13

      On multi-family residential and all commercial jobs that makes sense. For a single house build, I don't think I'd manage to get half the subs to attend, and they wouldn't typically be the same ones as did the work. To me the onus is on the GC to understand the implications of the build, how each phase of work affects the next, and communicate these individually to the subs as they come on-site. That's one the weaknesses of houses built without GCs.

      1. Expert Member
        BILL WICHERS | | #17

        I do mostly commercial work and I know what you mean. With no GC, I’d hope the homeowner has some kind of construction background. There is a lot going on on any build. In this case, The owner would need to visit the site frequently to make sure stuff doesn’t get missed.

        Honestly, with all the project screwups I see (I’m frequently acting as a combination of owners representative and an integration expert/consultant), it always amazes me construction projects ever get done right.

        Bill

        1. Expert Member
          MALCOLM TAYLOR | | #18

          Bill,

          The most common thing I find with no GC is that whoever is overseeing the work often makes assumptions about that a trade will do that are well outside of their scope of work - like assuming the kitchen installer will also put in and duct the range hood, or the siding sub will be happy to put on exterior foam.

          1. gfranke | | #19

            Just to clarify, there is a GC on this project, I am not acting as the GC. No way I would have been able to pull it off, for the reasons you describe.

  7. walta100 | | #14

    Generally framers use a 92 5/8 precut stud so with 2 top and bottom plate puts you at 97 1/8 less the thickness of the ceiling drywall ending up at 8’5/8” so the framers was wrong unless the plans called for an 8’ 2” ceiling or the drywall installer went out of his way to cut all the sheets short.

    The drywall installer should have seen the problem and installed the sheets sideways with a 2 inch gap in the center so he would have 1 joint to finish. Some would have changed their bid because it is more labor than planned.

    If Gordon has 2 ½ inch base board Do you think the wall will flex and crack the paint line every time someone bumps into the base with a vacuum cleaner?

    From here I would add the strip of drywall to leave a 1/4 gap one thin coat of mud for air sealing and consider selecting a tall base board.

    How tall will your base trim be?

    Walta

    1. Expert Member
      MALCOLM TAYLOR | | #15

      "The drywall installer should have seen the problem and installed the sheets sideways with a 2 inch gap in the center so he would have 1 joint to finish"

      Or used five foot sheets for the bottom boards.

    2. gfranke | | #16

      The walls where the gaps appear are topped by scissor trusses, so the ceiling is angled upward from the top of the wall. I also furred out the 2x4 studs using foam and wood strips (method discussed here). Both of those things meant that the drywall on the wall actually intersected the ceiling drywall an inch or two above the top plates. I'm sure that is the cause of the gap.

      It is disappointing when you hire supposed professionals who should know how to do things right, and then they don't. But it must be the human condition because that problem seems to ubiquitous and I have encountered it with just about every trade. It is surprising that the workmen have a supervisor checking their work, a GC checking over the work, an inspector checking over their work, and yet we the owners still discover problems that were missed by everyone along the chain. There is a reason why the inspector exists, and why everyone has bosses, people seem to just always be messing things up. That's why I'm terrified to visit the doctor.

      I give most of the guys leeway because I'm not aware of all the problems the chain of command DID catch and correct without me having to know about it, and I am not aware of the particular challenges they may have faced on our project. I also don't have the monetary leverage to be very demanding.

      Thanks for all the suggestions. I tested the tape today and it stuck, so I'm still figuring out what to do but tape will probably be involved.

  8. JC72 | | #20

    The 1/2 inch gap at the bottom is common practice in my area. I was told it's done so that carpet/hardwood installers can insure a well attached and/or hidden edge underneath the baseboards.

    What's funny is that whenever carpeting is used the edge of the carpeting becomes discolored because outside air is pulled in through this gap.

    1. Expert Member
      MALCOLM TAYLOR | | #23

      J0hn,

      Pre-cut studs for both eight and nine foot walls are sized to leave a 1/2" at the floor so you can get the drywall into place and allow for any uneven conditions. Less than that and boarding would be much harder.

  9. user-2895420 | | #22

    We have this EXACT same issue on a 20’ length of an interior basement wall. We just noticed it yesterday. The only difference is that we have mineral wool in our stud bays. We have 9’ high walls in the basement and it appears that they cut the top 1’ wide drywall sheets too narrow.

    I believe I can use canned spray foam to seal this small gap at the bottom of each of the stud bays, and simply cut off any excess that cures/protrudes outside the plane of the drywall – so it doesn’t interfere with the base trim.

    1. Expert Member
      MALCOLM TAYLOR | | #24

      Nancy,

      Do you know why they didn't just use five foot wide boards for the bottom of the walls? It's the standard practice and eliminates one taped joint.

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