Retrofit – adding spray/rockwool insullation on exterior
Hello,
We’re in southern Alberta, Canada (zone 3a, now 4b), planning to replace windows and add exterior insulation to our 1972-built house. The current setup includes 1/2″ drywall, a vapor barrier (poly), 3 1/2″ wood framing with standard fiberglass insulation, fiberboard sheathing, tar paper, and a stucco exterior. We intend to attach a 3-4″ deep grid to the existing stucco, fill it with insulation, and cover it with a house wrap. We’re considering finishing this with new stucco, either applied directly to the grid and insulation or on top of an additional layer of sheathing.
Our concerns are about the best insulation choice, considering potential issues with dual vapor barriers if we opt for closed-cell spray foam. Would Rockwool Comfortboard 80 be a better option? Also, for the stucco finish, should we apply it directly to the grid and insulation, or is it advisable to install sheathing in between? Or ppossibly creating an air gap with additional wood stripping and install sheeting and stucco on top?
Thank you in advance for any advice or feedback. We greatly appreciate it!
Cyril
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Replies
Nothing particularly wrong with Rockwool but if it were me I would do: Sheathing -> WRB -> rigid foam (EPS or polyiso) -> Delta Dry Stucco and Stone (or equivalent) -> stucco coats
The delta product acts as a rainscreen. There is enough micro annulus between the rigid foam and WRB on the sheathing that you won’t need to worry about trapping moisture and both of those surfaces will be resistant to rot (WRB and foam). But since you are doing closed-cell on the interior I would prefer a vapor-open WRB. Delta Vent SA is a decent choice.