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Exterior insulation over existing fiberboard & CCSF

asinger | Posted in Energy Efficiency and Durability on
As part of a whole home renovation we’re replacing the siding of our 1986 built house in Southern Ontario, climate zone 6.

Existing wall, outside -> in is:
– Aluminum siding
– 1⁄2” fiberboard sheathing
– tar paper weather barrier
– 2×4 studs filled with close cell spray foam
– 6mm poly vapour barrier

We’re looking to add exterior insulation and improve our air barrier. Our builder gave a couple options:

Option 1:
– Everlast composite siding
– 1x strapping rain screen (3⁄4”).

– R5 ROXUL Comfortboard 80 (1 1⁄4”) OR R5 XPS Rigid (1”)- joints not taped
– Blueskin VP100 (Air & WRB)
– Existing fiberboard sheathing
– 2×4 framing w. existing CCSF 

Option 2:
– Everlast composite siding
– R3 zip sheathing (Air & WRB)

– Existing fiberboard sheathing
– 2×4 framing w. existing CCSF 

For Option 1– the builder is concerned about the condition of the fiberboard sheathing and if the Blueskin VP100 will adhere, even with a primer. Has anyone used Blueskin VP100 over fiberboard and had problems with sticking?

For Option 2– this is the builder’s preference but i’m concerned about the sheathing not being able to dry out between the existing CCSF in the studs and R3 zip.

Do either of these options seem feasible or is there another approach to recommend for adding exterior insulation while using closed cell spray foam in the studs?

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