[Greenbuilding] Managing Sheathing as an air barrier.

[Clarke Olsen]

If you are prepared to go to the effort of sealing horizontal joints between osb sheets, you could put a dab (or run a bead) of construction adhesive 
and skip the clip. Or run the furring strips horizontally to back-up the joints.
I feel that structural sheathing should be installed horizontally: the grain of the panels (the "O" in OSB) should be perpendicular to framing.
The danger of redundant barriers is that a failure (harsh term, but you know what I mean) of one can mean moisture is trapped between.
Clarke Olsen
clarkeolsendesign.com
373 route 203
Spencertown, NY 12165 
USA
518-392-4640
colsen at taconic.net




On Jan 26, 2013, at 11:09 AM, Eli Talking wrote:

> As described in previous messages, I am planning on installing 12” eps foam boards on top of 7/16”osb roof sheathing with 2x4 furring strips at 2’oc for nailing corrugated roofing to.  The exterior walls are similar with 2x3 furring strips aligned with studs over 6”eps over 7/16 osb. 
>  
> I am planning the osb and eps rows to be perpendicular so that only at the intersections will there be a continuous potential leak.  I want to manage both the eps and the osb to be a continuous air barrier.  Only one is required to achieve performance.  However, the vulnerability to execution flaws, even when you are trying, makes me want to manage both layers to provide a redundant continuous air barrier. 
>  
> The osb would be installed conventionally with plywood clips between rafter top chords.  This creates a continuous gap the thickness of the metal clip.  Can someone recommend a tape that will not give up in time?  Would sealing it with acoustic caulk be practical, maybe from the top side?
>  
> The foam will be air sealed at the seams with acoustic caulk.  As a third air barrier, I might consider tape at the foam seams on top.  I am going to put a dab of caulk on the bottom of the furring strip where the pilot holes show where the screw will penetrate the full thickness to seal that potential leak.  Another potential air barrier is to cover all the foam with a plastic or tight building wrap before installing the furring strips. 
>  
> If I am able to achieve to my satisfaction the air barrier in osb and eps layers, I should not need the membrane layers. Since the foam is 6” and 12” thick, the nails from installing finished materials penetrating .5” or so into foam should not threaten the air barrier if it does not fall at a seam. 
>  
> You comments, as always will be appreciated. 
>  
> Eli
> www.conservationarchitect.net
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