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Tape seams of exterior sheathing on double-stud walls or not?

user-6865122 | Posted in GBA Pro Help on

Logging in–for the first time–from Schenectady, NY (5A)

We’ve already put up ship lap (reused and new) or 1/2 plywood on exterior of our double-studded wall first floor addition. I had imagined the next step–before putting on house warp, furring strip rain screen, and (the original) cedar shake siding–would be to tape the ext. seams, perhaps with Siga Wigluv or like product. But then, upon reading on GBA more about double studded walls, particularly the importance of using vapor permeable sheathing, wondered if taping the exterior walls would create a problem in terms of moisture build-up in these walls.

I look forward to the responses of those with experience in the construction of double studded walls!

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Replies

  1. STEPHEN SHEEHY | | #1

    We may have gone overboard, but we taped the sheathing seams as well as the housewrap seams on the exterior walls of our double stud build. Mostly we used 3M 8067 flashing tape on the sheathing.
    Instead of airtight drywall as Steve Knapp suggests, we put a membrane (Siga Majpel) on the outside of the inner stud wall. I think either option works.

  2. GBA Editor
    Martin Holladay | | #2

    User-6865122,
    First of all, can you tell us your name?

    There is a difference between vapor permeance and airtightness. While there is certainly an advantage to vapor-permeable sheathing (especially for a double-stud wall), there is no advantage to sheathing that has air leaks. Airtightness is always good.

    If your sheathing consists of 1/2-inch plywood, it makes sense to tape the plywood seams. For more information, see Airtight Wall and Roof Sheathing.

    If your sheathing consists of re-used shiplap boards, you can't really tape the seams (because there are so many seams). With board sheathing, you are better off trying to make the housewrap layer as airtight as possible rather than trying to make the sheathing layer airtight.

  3. user-6865122 | | #3

    Thanks for your prompt respective replies, Steve, Stephen, and Martin. Very helpful, indeed.

    To respond to Martin's question, my name is Daniel Carlson. And bit more about our project: my adult sons, wife, and I are building--with the generous help of more experienced friends--a long anticipated south facing addition that includes a new car port and covered porch, a reoriented mudroom, a new kitchen, all over a basement that we anticipate will be a pottery studio. Its a combination of double studded walls (interior) and hemlock timberframe (carport and covered porch).

    I just ordered several rolls of Wigluv 60 from Sigatapes and the primer that can be used with it (for the concrete - plywood connection), plus a sampler pack for further consideration of use of their products.

    Thanks again!

  4. user-2310254 | | #4

    The 1/2 ply is vapor permeable, and you definitely want to tape all seams. The objective is to prevent water and air infiltration from the exterior. You also want to install the drywall in an airtight fashion to prevent conditioned air from entering the wall from the interior.

  5. user-5574861 | | #5

    Daniel,

    I have been using both Wigluv and Fentrim from Siga on my current project. I prefer to use Fentrim on the concrete to sill/sheathing connection or any area that may wrap around edges because it sticks extremely well to rough surfaces, without a primer, and will not tear. The Wigluv will tear/puncture, so I use that on areas that are less likely to tear, like wall seams.

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