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Community and Q&A

Taping OSB sheathing AND EPS?

ken_o | Posted in Energy Efficiency and Durability on

Hello,

House project:  Zone 7, 2×6 walls with R-19 fiberglass, then 30 lb. felt WRB, (3) 2″ layers of EPS, 3/4″ furring strips and cedar siding.

Questions in regard to seam taping:
1) Should I tape the seams on each EPS layer?
2) Should I also tape the OSB sheathing seams? 

Thanks.

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Replies

  1. jwolfe1 | | #1

    Great question. I'm curious as well.

  2. Expert Member
    MALCOLM TAYLOR | | #2

    ken_o,

    What were you planning to use as your primary air-barrier on the walls?

  3. Expert Member
    Akos | | #3

    You need a solid air barrier, sheathing is the easiest to detail and tie into the foundation and ceiling, so I would tape the OSB.

    The layers of foam don't need to be taped as long as you stagger the seams. Once you stagger the seams the air paths are so long that you won't get much convective air flow between layers. Taping doesn't hurt but I don't see it being worth the time.

    The one change I would make is to use a 1.5" layer of EPS in the middle and embed some 2x3 or 2x4 on flat. The simplest would be to get 2' wide foam and run the 2x horizontally between them so you don't have to do much foam cutting. This would let you use much shorter screws and a 2x on flat is a much easier target to hit for your rains screen strapping. Trying to hit 1.5" wide target through 6" of foam with 10" screws is possible but not fun. Plus 5" screws are much cheaper even if you need more.

  4. ken_o | | #4

    Thanks for the thoughts. Very interesting idea with the 1 1/2" layer of EPS and the extra 2x4s (or ripped 2x6s). I would be losing about R2 all around and a bit more at the studs. However, I can see the value of having an easier target to hit with the screws. We built the garage this summer and even though we only used a single 2" layer of EPS there, we missed the studs several times! (Yes, we plugged the holes). Going through 6" of EPS would be a challenge.

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