This concern was analysed in the NRC research document, “Report on Properties and Position of Materials in the Building Envelope for Housing and Small Buildings.” Four geographical locations were reviewed that included Ottawa, Edmonton, Vancouver, and St. John’s and five types of exterior insulation with a thermal resistance of R4 were analysed that had vapor permeances of 2 ng/Pa•s•m2, 60 ng/Pa•s•m2 , 90 ng/Pa•s•m2, 300 ng/Pa•s•m2, and 1800 ng/Pa•s•m2.
The findings concluded:
- More cavity insulation increases the risk potential for condensation at the exterior sheathing interface
- Exterior insulation reduces condensation risk potential at exterior sheathing interface
- No significant difference in condensation risk potential between the five insulations
These finding resulted in the National Building Code (NBC) of Canada lowering the trigger point for the inboard and outboard calculation to a vapor permeance of 30 ng/Pa•s•m2 for any exterior insulated sheathing (i.e. continuous insulation).