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Community and Q&A

Airtight drywall

Zampano77 | Posted in Green Building Techniques on

I want to caulk and foam all joints in my framing prior to hanging drywall. Is there a difference in latex caulking and is there a best one when it comes to providing an airtight seal for air barrier? I will be hanging glued and screwed OSB on the interior side of the studs for stiffening an old house, will the same caulk and or gaskets be fine to install the OSB as it would on drywall.

When construction adhesive is used on the drywall or OSB, will that effectively act as an air seal on the faces of the framing or should one use gaskets and if so, what is recommended. I have used Denarco gaskets years ago, are these still advisable? Recommendations of sealants that have good value and performance would be great.

Lastly, when a INSULATED service cavity is used on the interior of the the sealed exterior walls ( mine have a OSB layer to stiffen a squeaky house, should the Intello or such be against the OSB and the service cavity built on top of it or should the smart wrap be directly behind drywall.

Attached is a drawing from:

Thanks for all past help.

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, here are two resources of information on the Airtight Drywall Approach:

    Airtight Drywall

    Video: How to Hang Airtight Drywall

    In his video on GBA, Myron Ferguson shows how he uses ordinary latex caulk when installing airtight drywall. If you can afford to upgrade to Denarco gaskets (or gaskets from Conservation Technologies), you won't regret the upgrade.

    If you want to use a layer of OSB as an air barrier, you might want to use tape, not caulk, to seal the OSB seams. High quality tapes include Siga Wigluv, 3M All Weather tape, or Zip System tape. (For more information on tapes, see Return to the Backyard Tape Test.)

    Finally, you might want to consider the fact that some brands of OSB are not airtight. For more information on this issue, see Is OSB Airtight?

  2. Zampano77 | | #2

    Thanks for the info. I did not know about all OSB not being equal in AT respect, great info. I have previously watched the AT drywall video and I was wondering if he indeed was using latex caulk. My question is there a reason to have a more flexible caulking than latex ( Sika Sikaflex-201 US, Tremco Dymonic FC Polyurethane, both $6.00 a tube or CONTEGA HF $13.80 tube= ouch! ) on the framing and connections.?? Just curious from your experience.

    I also want to glue ( and air seal if possible) the interior structural layer of OSB on the inside of the existing wall and wondered if you could make recommendations to an glue that could do both? I will definitely tape the OSB joints after install with one of your recommendations- thanks.

  3. GBA Editor
    Martin Holladay | | #3

    Ordinary construction adhesive will work fine for gluing the OSB to the framing.

    In general, more expensive caulks will probably be more flexible and durable than less expensive caulks. Whether expensive caulk is needed for airtight drywall is a judgment call. The information below comes from a Fine Homebuilding article called "Caulk This Way."

    Often the least expensive
    choice, these water-based
    caulks cure by evaporation.
    Consequently, they can shrink
    by a quarter to a third of their
    volume before they’re fully
    cured. They hold paint well and
    usually can be painted within
    four hours. Most aren’t as
    flexible as many other sealants,
    but they’re a good choice for
    filling small gaps between
    interior-trim pieces.

    The original modern sealant,
    butyl dates from the 1920s. It
    cures through the evaporation
    of organic solvents, shrinking a
    quarter to a third in the process.
    Butyl is sticky and can be harder
    to tool than other sealants,
    but it can be used in freezing
    weather. Best used outdoors
    because of its odor before
    curing, butyl is less common in
    residential construction than
    other sealants.

    So-called STPE (silyl-terminated
    polyether) sealants are similar
    to and sometimes superior to
    polyurethanes. Relatively new
    to the U.S. market, STPEs have
    been used in Japan for decades.
    Based on polypropylene glycol,
    they cure by reacting with water.
    The cure rate is much faster
    than that of polyurethanes, and
    STPEs can be painted sooner.
    They can be used on damp
    surfaces and in below-freezing
    temperatures, making them a
    good choice for outdoor use.

    Although urethane cures by
    reacting with moisture, it
    shouldn’t be applied to wet
    surfaces or when rain is in the
    immediate forecast. An excess
    amount of water can cause
    a reaction that releases an
    undesirable amount of CO²,
    which can cause the sealant
    to froth and compromise its
    ultimate strength. Although hard
    to tool, polyurethane sealants
    are paintable, long lasting, and
    abrasion resistant.

    These SPUR (silyl-terminated
    polyurethane) hybrids have
    characteristics similar to STPEs.
    Like STPEs, SPURs rely on
    groups of a long-chain polymer
    (in this case, polyurethane) for
    the backbone of the sealant,
    and groups of a second polymer
    (silyl or silane) for the ends. The
    long-chain polymer provides
    both elasticity and cohesive
    strength, while the silyl endcaps
    provide adhesion.

    Early versions of silicone caulk
    had a so-called acid cure and
    released a vinegar smell. Modern
    silicone cures by reacting with
    moisture and gives off very
    little odor. Silicone bonds at a
    molecular level with glass, making
    it a good choice for frameless
    shower doors and tile. It doesn’t
    take paint, and not even silicone
    sticks to where silicone has been
    used before, so recaulking usually
    requires mechanically removing
    some of the previous substrate.

  4. dankolbert | | #4

    You also might want to consider EPDM drywall gaskets from Conservation Technologies. No mess, can be installed long before drywall installation, permanent flexibility.

  5. GBA Editor
    Martin Holladay | | #5

    I made the same recommendation, and provided a link to Conservation Technologies, in my first response. (I'm glad we agree.)

  6. Zampano77 | | #6

    Thanks for the information. Can anyone give me a response on the last part of my submission if possible.

    "Lastly, when a INSULATED service cavity is used on the interior of the the sealed exterior walls ( mine have a OSB layer on the inside surface of the studs to stiffen a squeaky house?"

    Should the Intello or such be against the OSB and the service cavity built on top of it or should the smart wrap be directly behind drywall?

  7. GBA Editor
    Martin Holladay | | #7

    OSB is a variable-permeance vapor retarder. It's already a "smart" vapor retarder.

    If your only source of information about the need for the Intello vapor retarder comes from people who sell Intello vapor retarders, you may want to ask others for advice. The OSB can be your air barrier (as long as you don't choose a leaky brand of OSB), or the drywall can be your air barrier -- and the OSB can be your smart retarder. In other words, you probably don't need any Intello.

    For more information on service cavities, see Service Cavities for Wiring and Plumbing.

  8. dankolbert | | #8

    I'm much better at advice than reading.

  9. LenMinNJ | | #9

    You might also consider using a spray foam to seal the sheetrock to the framing. That seems to be what our modular home manufacturer did for the double-framed four main module walls in our northern New Jersey passive house. We passed our blower door test with no problems.

    The insulation in the cavity is densepack cellulose. The outer sheathing is Zip System. And we have 2-inches of Type 1 EPS foam over the Zip System.

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