More Energy-Smart Details
When it comes to control layers for managing water, air, vapor, and heat movement, continuity is key. This month, I address the air barrier specifically. Rather than illustrating a detail with the air barrier on an even plane, this detail demonstrates how to switch from the vertical plane of a wall to the horizontal plane of a ceiling without any gaps. There are many ways to go about this detail. In this case, the parameters driving the decision were cost, buildability, and durability.
Note the Zip sheathing on the wall plane; it is not only the exterior closure for the stud cavity, but also the primary exterior air barrier. In combination with the AdvanTech sheathing, it adds structural integrity as a shear panel. (The reason for using AdvanTech rather than, say, rips of the Zip sheathing is that it is dimensionally similar to the 1×3 strapping. The Zip is 1/2 in. and the strapping is 3/4 in., which means rips of Zip would require changing the strapping to something closer in size.) When working with Zip sheathing, all joints are wiped clean, taped, and rolled to provide the proper seal between panels.
On the ceiling plane, the gypsum board is installed as the primary air barrier, and the taped seams provide continuity. One of the challenges at the ceiling is interior partitions. One approach is to install the drywall prior to adding interior partitions. This ensures a wide-open ceiling plane without interruptions. With the exterior air barrier at the wall and the interior gypsum board at the ceiling, the challenge becomes creating continuity at their intersection.
Here, the wall assembly is a double-stud frame—though a similar detail can be used for single-framed 2×6 and 2×8 walls. For continuity at the intersecting planes, the air barrier is folded 90 degrees from the wall to…
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8 Comments
If you were to use this detail how would you tie hurricane straps from the truss to top plates? Truss screws?
Truss screws typically, or you could use standard truss ties prior to placing the upper Zip piece outside the blocking.
Do you specify longer screws to account for the additional osb thicknesses?
Question re the exterior detail where wall sheathing is taped to Advantech. Is the Advantech a strip that is allowing a rain screen? If so then why the tape and why not simply use strapping? If the Advantech is full sheets then why use the OSB Zip sheathing? I'm clearly misunderstanding something here.
Thanks
Richard
Richard, please understand the 3/4 inch Advantech has multiple purposes. First and foremost it seals the double stud cavity from the attic in reference to fire transfer. As part of the air barrier it is simply a bridge that connects the exterior zip sheathing to the drywall interior air barrier at the ceiling.
Hi Alexandra,
Thanks for your response. I have added a screen capture that I hope will make clear where my confusion came from. I now realize that I didn't look at the drawing close enough however if you look at the reference to the 3/4" Advantech on the right of the drawings I think you will understand where my question was coming from. It looked like the 3/4 Advantech was the 1 by 3 strapping... Thanks for clarifying.
Richard, yes, there it is calling out the tape is connecting the joint of wall sheathing to the 3/4 inch Advantech. The reason for the confusion most likely comes from the tape is shown as a faint dashed line so if you don't see the dashed line easily it looks like it is pointing to the strapping.
I’ll be using Zip R-9 as my exterior air barrier, but I won’t be using strapping between my trusses and drywall. We just don’t do that here in the Midwest, at least not here. What would be the best and easiest way then to tie the exterior zip wall to the drywall? I’m thinking there must be a way to just use some poly or Tyvek or something to wrap around the top plate, tape to the zip and caulk to backside of the drywall or something… I’ve been searching for hours and all I can find is this osb/strapping technique? Anybody have a link or info on using something like I’ve described?
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