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Air sealing specifics: OSB and WRB

Zane Bridgers | Posted in Green Building Techniques on

Hey There Folks –

Excuse me if this is a bit repetitive, but I’m working through a few details air sealing our house and had some questions come up.

1 – Any issues with sealing from the bottom of the osb to the eps foundation foam? I’m not sure the 3M All Weather 8067 will seal to the EPS, so was considering spray foam or caulk. We left an 1/8 inch gap as a capillary break below the osb, and bottom plates have sill seal and two beads of caulk, but the osb is not sealed to the bottom plates.

2 – Should we seal the edges of the window and door rough openings? They will get flashed later but integrated with the WRB, which seems like a different layer, and I take it WRB’s are not generally air barriers. We plan to use Tyvek Stuccowrap or Commercial Wrap D.

3 – Any improvement in 3M Red Tape (8087) over Tyvek Tape for the WRB?

By the way, got my hands on a really nice fluke thermal imaging camera. What an awesome tool! I’m really excited to put it to the test once the exterior foam is on, and going forward. I’ll try to post up some photos throughout the process.

Cheers,
Zane

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Replies

  1. User avatar
    Dana Dorsett | | #1

    In most places code requires Z- flashing at the transition from the wood framed wall to the foundation, which where your foundation foam meets the wall foam. It's fine to use something less thermally conductive than metal though. Six inch EPDM flashing tapes can perform that function with 2" foam, maybe even up to 3" , but fatter foam than that it's bit of a pain.

    1. Zane Bridgers | | #2

      Thanks Dana! It seems most stores carry 1/2 or 5/8” z-metal and no one local here has epdm tape. Where does this z-flashing go on a wall assembly with exterior foam. Is it supposed to go under or over the osb? - to I assume the outside of the foundation foam? Seems I would need 2” z-metal which may make ordering epdm tape the more flexible option.

  2. Zane Bridgers | | #3

    Could I politely bump the question of whether or not it is necessary to tape the around the window/door rough openings as part of the OSB seam sealing?

    In Matt Risinger’s video, it appears he does not tape the rough openings, just the seams...

    1. Malcolm Taylor | | #5

      Zane,

      As Brian says, it needs to get sealed one way or another. It depends on how you intend to install the windows whether it gets done at the same time as the sheathing or later. If the WRB is going on before the windows and folded into the opening, the intersection of the OSB and framing should already be sealed. If after, only the head probably needs to be sealed first.

  3. User avatar
    Brian Pontolilo | | #4

    Most WRBs are air barriers, in that air cannot pass through them, but they are not often used as a primary air barrier because they are difficult to detail well. It may be that Matt used sealant around the perimeter of the OSB panels for an air seal or that he will seal those edges as part of the window flashing details, or that he'll be using spray foam to air seal between the window frame and the rough opening and thinks that will do the trick. There are lots of possibilities, but the area will need to be air-tight one way or the other.

  4. Zane Bridgers | | #6

    Thanks guys! It makes sense of course that it should be sealed at some point, but I wasn’t clear if the window flashing process and spray foaming was assumed to take care of it. Will be installing the WRB before the windows so I will seal those rough openings now.

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