Jeremy writes from Toronto, Ontario, Canada: "I live in a recently renovated 100+ year old house which was renovated by the previous owner. The walls are standard wood frame assembly. Gypsum board interior face, vapour barrier, wood stud between which there is fibreglass insulation.

"Question: I have replaced the windows and I am currently removing the exterior vinyl siding and tar paper substrate. I would like to apply a 2" thick layer of rigid insulation over the exterior face of the walls before installing new siding. I am concerned that I have 'trapped' or will trap moisture within the wall assembly between the 'warm' inside vapour barrier and exterior (impermeable) rigid insulation. Should I be concerned?"

Answer: No. Though 2" foam insulation (I recommend PINK FOAMULAR® insulation, naturally) has the characteristics of a vapor barrier, it cannot solely act as one. If you have multiple products with vapor barrier characteristics, you need to place the strongest vapor barrier nearest the warm air. Therefore, your application will work.