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air barrier at sheathing vs exterior insulation face

jollygreenshortguy | Posted in Energy Efficiency and Durability on

This is about where to put the wall air barrier.
Also, for this question I’m not considering the interior drywall as the primary air barrier.
Your opinion regarding the most practical approach from the 2 options presented is welcome.
The wall section consists of:
* cedar siding over 1x furring (rainscreen), over
* 2 1″ layers of EPS Type IX, joints staggered, (R10), with outer layer taped to serve as the WRB, over
* plywood sheathing, over
* 2×6 framing @24″ oc with R20 cellulose batt insulation
* Interior drywall with vapor open paint

Option 1 – The taped EPS can serve as a WRB and save a step. With a small amount of additional taping it could also serve as the air barrier.

Option 2 – Alternatively, the plywood sheathing could be taped as the air barrier.

Would you tape the EPS or the plywood? Yes, obviously both can be taped but if reducing labor is the goal and you can only tape one, which is it.

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  1. maine_tyler | | #1

    I think the general concensus is that taped sheathing is a more robust and easy to detail air barrier. Foam shrinks and tape won't stick quite as tenaciously. But if you tape the sheathing, you would be adding a wrb? A separate wrb may also be easier to detail than taped foam at window and door openings? No experience with that difference, just guessing.

    I forget what climate zone you are in. Have you checked that you don't need a class II vapor retarder, even with the R10 exterior?

  2. Expert Member


    As maine_tyler says, it's a lot easier to detail the sheathing, not only in the field, but at transitions like openings, the foundation, and to maintain continuity with the air-barrier on the roof.

    Taping foam to reduce the possibility of water infiltration makes sense to me, but I don't know how confident I'd be in relying on tape to seal flashings when it is used as the WRB. It seems to work on Zip, but that's a solid substrate with a proprietary tape.

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