Vertical Rain screen wall in climate zone 4C

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Vertical Rain screen wall in climate zone 4C

I am an architect designing a house on Salt Spring Island which is in Climate Zone 8. The code mandates rain screen and the client desires vertical red cedar ship lap boards. The house has very high ceilings at 14' and 12' which requires a fire break at 10'. My questions are to do with how to best design the wall to mitigate humidity inside the house and create the most energy efficient house possible for the owner.

My current wall build up is:

1/2" Wallboard with latex paint
2x6 stud wall construction with R21 Owens Corning fiberglas insulation
1/2" OSB sheathing (also to create the required shear walls)
2" rigid insulation taped acting as a Class II vapor barrier.
7/16" Cor-a-vent attached at 24 inch centers horizonatlly as a nailer for the vertical boards
3/4" vertical siding.

Total roughly 9 3/4"

My concerns are with the rain screen strategy using the cor-a-vent. It seems a strong enough product to use but certainly doesn't comply with recommended 1 1/4" to 1 1/2" nail depth for the siding. Also will 2" rigid insulation be enough in climate zone 8 to bring the dew point outside of the structure? I have read in some blogs that it should be more like R15 vs the R10 which I have.

Also I am not including an interior poly on the studs as I am assuming the wallboard/primer and latex should suffice.

I would very much appreciate any comments/suggestions to the above. Thank you!


Asked by Marcus Springer
Posted Thu, 12/06/2012 - 16:26
Edited Fri, 12/07/2012 - 10:40