Azek PVC sheets goods over 1 1/2 foam board as siding
William Campbell| Posted inGreen Building Techniqueson
Looking for some feed back on a wall system i would like to assemble on an addition with very little wall space, Mostly glass windows
Wall system: From in to outer ,
1/2 blue board
2×4 wall 16 in OC
R-15 batt insulation with in wall cavity area
1/2 plywood sheathing
Outie windows installed on 1x material applied to sheathing
Tyvek house wrap
1 1/2 foam insulation installed, taped and foamed seams and edges
Tyvek house wrap applied over Foam and tapped seams and tapped to window nailing flange
Azek sheet goods as sheathing and trim around doors and windows
Looking forward to hear some feed back on this wall assemble
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Replies
William,
Your proposed wall assembly appears to have an R-value of R-7.5 (if you use XPS) or perhaps R-10 (if you use polyiso foam). As far as I know, such a wall assembly won't meet minimum code requirements anywhere in the U.S.
Even in Florida, the code requires framed walls to have a minimum R-value of R-13.
From a moisture standpoint, the wall assembly would work as long as it can dry to the interior. That means you should never install interior polyethylene or vinyl wallpaper. As with any type of siding -- but especially with a vapor-impermeable siding like Azek sheet material -- a wall assembly will be less risky if you include a rainscreen gap between the siding and the sheathing.
Oops forgot to list the R-15 bat insulation in the wall cavity
William,
What is your location or climate zone?
Climate 5a
William,
Your assembly will work in Climate Zone 5. But I still strongly advise you to include a ventilated rainscreen gap between your siding and your sheathing. Because your siding is vapor-impermeable, the exterior of your wall assembly is unforgiving. The rainscreen gap is cheap insurance to limit the risk of moisture problems.
Thank you Martin, Good advise i will definitely add a rain screen between behind the Azek Material