Retrofit exterior insulation over fiberglass and polyethylene interior – high performance
Hi! New member here.
I’m looking for suggestions to retrofit insulation from the outside to a 30-40 year-old home in what I think is climate zone 5b, north of Kingston, Ontario, Canada, County of South Frontenac.
The home is built with 2×6 walls and (TBC) 2×10 rafters providing a cathedral ceiling, seemingly all insulated with fiberglass and polyethylene “vapor barrier” to the interior.
We would like to re-do the exterior siding, and would like to take the opportunity to add further insulation before replacing cladding with Hardie shingle. I would like to have a long-term plan for the roof, but will be a later event.
I would prefer to go foam free, if possible, but cost is also a major consideration.
What would be an appropriate assembly for walls only? Walls and Roof? How would I tie in a later roof insulation?
Would the recommended assembly allow drying to the exterior?
It seems that slapping on polyiso could trap the moisture? Or is it permeable enough?
My first inclincation is rockwool rigid panels for the walls, for general ease, cost, availability, and vapor permeability.
I’ve never seen a rigid rockwool panel used on the topside of pitched roof sheathing, locally… Final roof is and always will be steel.
Shooting for R-40 walls, R60 roof. Seem reasonable?
But maybe that will require TJI outriggers or some such…
Any thoughts appreciated!!!
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