6 mil Poly and Exterior Foam Insulation
Polyethylene vapour barrier and exterior foam insulation?! I know, I know… trapped moisture, don’t do it. BUT… I see tons of walls built this way everywhere in Canada! Typically: drywall, 6 mil poly, 2×6 stud cavities with pink batts, cheap housewrap and ~R5 continuous exterior foam insulation.
And as has been previously mentioned on this topic, we do not see widespread failures of these in regular houses (without pools, greenhouses, etc.) “up north”.
I am in climate zone 6. My question is: if I have more than R5 continuous insulation, say R10 or R15, does this get more risky? Why don’t the R5 walls have more issues? Does it make a difference to your answer if I am taking the time to carefully install the materials myself (as opposed to a builder on a fixed budget) or are the risks inherent to the system as opposed to poor installation?
Vapour permeable membranes, better WRB’s, vapour open Comfortboard… these are all great products but with considerably higher price tags, so I am trying to dig in to the risks of the “cheap” products if used well.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part