Replies

1. GBA Editor
   Martin Holladay | Apr 18, 2017 06:42am | #1

   Inger,
   What's the purpose of the housewrap? If it's not your WRB, perhaps it's your exterior air barrier? Or is it something else?

   If it's your exterior air barrier, you might consider omitting it and just taping the sheathing seams.

   If you want to use housewrap as an air barrier, you can, but you need to take care of it during installation, because it is fragile. To detail the housewrap as an air barrier, just use housewrap tape at the window bucks.

   Using rigid foam as your WRB is possible, but many people find it easier to use housewrap as a WRB (because housewrap can be lapped). For more on the use of rigid foam as a WRB, see this article: Using Rigid Foam As a Water-Resistive Barrier.

   You might also be interested in reading this article: Where Does the Housewrap Go?

   -- Martin Holladay

2. 
   PatriciaCranberry | Apr 25, 2017 03:04pm | #2

   So no harm will befall my osb sheathing if I put 1" rigid foam directly against it and then apply the house wrap over the rigid foam? I am planning outie windows so it would just require normal techniques for flashing. But alternately, you don't see a conflict with placing house wrap against sheathing, taping to the outside corner of sheathing/window buck and then applying rigid foam and flashing window as usual? kinda belt and suspenders?

3. GBA Editor
   Martin Holladay | Apr 25, 2017 03:15pm | #3

   Inger,
   Q. "So no harm will befall my OSB sheathing if I put 1-inch rigid foam directly against it and then apply the housewrap over the rigid foam?"

   A. No, as long as your flashing and water management details are well-thought-out and well installed.

   Q. "You don't see a conflict with placing housewrap against sheathing, taping to the outside corner of sheathing/window buck and then applying rigid foam and flashing window as usual? kinda belt and suspenders?"

   A. I'm not sure why this is a belt-and-suspenders approach. And I don't know what you mean by "flashing the window as usual."

   Here's the most important point: You need to know where your WRB is. You can use rigid foam as your WRB if you want, or you can use housewrap as your WRB. If you use rigid foam as your WRB, the housewrap is unnecessary but harmless.

   -- Martin Holladay

4. 
   brendanalbano | Apr 25, 2017 03:46pm | #4

   If you're using outie windows and rigid foam, it makes sense to me locate your WRB on the outside of your rigid foam. Then everything is all lined up.

   Assuming you want to use housewrap (as opposed to relying on your foam as your WRB), your wall ends up being:

   - Lap siding
   - 1x4 furring
   - Housewrap (this is your WRB)
   - 1" rigid foam
   - OSB with seams taped (this is your air barrier)
   - Structure
   - Interior finishes

   Check out the diagram called "Sidebar I: Installing Windows in Housewrap Openings" in this article to see how to integrate the flashing and the housewrap: https://buildingscience.com/documents/insights/bsi-067-stuck-on-you Note that that diagram doesn't show your 1" of foam board between the housewrap and the OSB, so you'll have to use your imagination for that part ;)

   Also note, if you choose to use your foam as your WRB, "Sidebar II" in the above article as the conceptual diagrams for how to flash your windows.

5. 
   alex265 | May 06, 2017 07:32am | #5

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6. 
   PatriciaCranberry | Jun 09, 2017 02:06pm | #6

   Brendan/Martin.Thanks. I heard the "buildings need to breath" speech last night from my builder. And today I bought a case of Sigawigluv and will be installing the tape myself, if needed. A little sweat equity.
   I will use the layout in Brendan's email above. Given that list, is there a need to also tape the rigid foam or just the housewrap?

7. GBA Editor
   Martin Holladay | Jun 09, 2017 04:20pm | #7

   Inger,
   Every wall needs an air barrier. If I had to choose between making the air barrier at the sheathing layer, at the rigid foam layer, or at the housewrap layer, I would choose the sheathing layer (as long as the sheathing is OSB or plywood, not boards). If you take my advice, the sheathing seams will need to be taped.

   Is it also necessary to tape the rigid foam? That's up to you. Taping each layer usually reduces the air leakage rate, so your decision depends on your goals and your budget.

   When it comes to the housewrap, most housewrap manufacturers require (in their published installation instructions) that the housewrap seams to be taped. To tape housewrap seams, use housewrap tape, not Siga Wigluv. (Housewrap tape is cheaper.)

8. 
   PatriciaCranberry | Jun 15, 2017 04:22pm | #8

   Tape arrived and I got started taping last night! I'm doing all seams and rough openings and I plan on applying the tape at the joint of the sheathing and concrete slab. My rigid foam goes up next. The sheathing outer edge is even with the bottom of the sill board/flush with the concrete slab outer face, sitting on top of the foam sill gasket This is a solid concrete slab-no exterior slab insulation proposed (climate zone 3). What's the minimum suggested overlap between the rigid foam beyond the concrete/sheathing line? Would 1-2" overlap be sufficient? With a flashing first against the osb, then rigid foam;housewrap/furring/insect screen/water table board. I'll just shingle from low to high two layers of 2.25 in siga wigluv tape to get a good seal between concrete and sheathing. Planning on 6" of exposed slab between end of LP smartside and finished grade.

9. GBA Editor
   Martin Holladay | Jun 15, 2017 04:28pm | #9

   Inger,
   Q. "What's the minimum suggested overlap between the rigid foam beyond the concrete/sheathing line? Would 1-2 inch overlap be sufficient?"

   A. Two inches sounds adequate to me. In northern climates, builders sometimes continue the rigid foam right down to the footing level -- below grade as deep as you can afford. But your geographical area may have enough termites to make this impossible.