Minimum exterior insulation requirements
Martin, recently you published a link to the BC Builder’s Guide for Effective Walls.
In it the guide states that to achieve the minimum requirement of a R22+ wall it should have:
2 x 6 Studs (R-19 Batts) + 1 1/2″ of R-4/inch or R5/inch Ext. Ins.
The guide further states that “This is acceptable across BC and that this level of thermal performance is required by the 2014 Vancouver Building By-Law and the 2012 BC Building Code for climate zones 7B and 8”.
I will be building in climate zone 6 so I figure that this wall assembly must be sufficient there as well. However, in your article “Calculating the Minimum Thickness of Rigid Foam Sheathing” you state that for climate zone 6 you need R 11.25 for exterior sheathing on a 2×6 wall and for zones 7 & 8 you need R 15.
BC seems to require much less exterior insulation than what you advise. Which method is correct? Also, since your article on foam sheathing refers to rigid foam do you need even more insulation if you use exterior mineral wool panels (since mineral wool allows more air to pass through it than a solid piece of foam)?