Double exterior wall question
Since I already own the OSB sheathing for our new central Indiana home, I’ve been stressing over all the concerns with using OSB in a double exterior wall assembly. I’m trying to come up with a solution that keeps my sheathing on the exterior of the double-wall assembly – and prevents it from turning to oatmeal!!
Is there a concern with assembling the exterior wall as follows:
1) Frame 2x4 exterior structural walls. The sole plates would sit on top of foundation. The interior walls would rest on top of floor system.
2) Apply membrane (Tyvek, 6 mil poly or even 45 mil EPDM?) to outside of wall framing – from top of foundation and terminate above attic insulation. This would serve as the air barrier and vapor retarder – the purpose for this is to reduce the high levels of summer humidity from migrating toward air-conditioned space.
3) Install vertical 1x4 strapping to wall studs (on top of membrane). No horizontal strapping – only insect screens at bottom and top. The ¾” air space allows air flow between the exterior sheathing and the membrane/wall cavity insulation.
4) Install OSB sheathing
5) Install water barrier (Tyvek or 2 staggered layers felt paper)
6) Install vertical 1x4 strapping on top of water barrier (Again - no horizontal strapping – only insect screens at bottom and top). This allows air flow between cement lap siding and water barrier/OSB. (Also allows me to gun-nail OSB and furring rather than screw through add’l thicknesses of an exterior foam board assembly)
7) Install horizontal cement board siding.
8) Inside: Install 3” rock wool insulation against the vapor retarder and fill the remainder of the wall cavity w/dense packed cellulose. Cover interior walls/ceilings w/drywall.
I believe this technique will keep the OSB as dry as possible, but am concerned with potential for winter humidity coming from within the home and condensating on the vapor retarder. I could use insulation netting instead of the vapor retarder, but am more concerned with drawing the summer humidity into the walls.
Any thoughts on this?
Posted Tue, 03/05/2013 - 06:16
Edited Tue, 03/05/2013 - 09:25
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