EPS as continuous insulation in above-grade, rainscreen cavity walls
We are building a house in Toronto, Canada. By code we need interior poly, so our walls need to dry to the exterior. The assembly is:
6 mil poly (vapour retarder)
2x6 wood studs @ 24" o/c w. R22 Roxul in the stud bays
1/2" plywood sheathing
Tyvek (drainage plane / air barrier)
1" continuous rigid insulation
1x4 PT wood strapping (fastened through rigid)
marine grade plywood or painted hardie board panels as cladding
My question is- because the exterior rigid will be continuous, I am concerned about limiting the exterior drying potential by using XPS. Conversely, I am also concerned that the EPS will be crushed when we fasten the battens through it, and would prefer XPS for that reason. I have located a high density EPS (Atlas XGrade), but even that product has a pretty tight vapour transmission rate, and its much more expensive. Because our air barrier is at the Tyvek, I don't plan to have them tape the rigid.
- Has anyone had success fastening battens through EPS?
- I have a consultant up here that tells me that local builders have used 1" continuous XPS with success for years, and that only if the exterior rigid was thicker would we start trapping moisture in the walls. What do you think about that?
Posted Jun 24, 2014 7:29 PM ET
Edited Jun 25, 2014 6:36 AM ET
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