Exterior insulation retreofit – GreenBuildingAdvisor

Hello All, 

I’m working on a retrofit of a large 1980s passive-style A-frame in coastal Nova Scotia (~5,000 sq ft). Previous siding work (on gable walls) was done poorly – new cedar shingles and metal cladding were installed over the existing siding with very little attention to window or door flashing.

The clients now want to strip the walls and rebuild the exterior properly with a rainscreen.

Current wall assembly appears to be:

• 2×6 framing

• spray foam in the cavities

• 1/2″ plywood sheathing

• 1.5″ foil-faced foam with taped seams

• siding

The windows and doors are currently set at the plane of the exterior foam.

If we strip everything back to the plywood, I’m considering two approaches:

1. Install ZIP-R sheathing to add continuous exterior insulation and a taped WRB in one step.

2. Install a separate WRB and exterior insulation over the existing sheathing, followed by a rainscreen.

My other question concerns the existing windows and doors. Ideally I would leave them in place to avoid disturbing interior trim, but that would require integrating the new WRB and insulation around the existing flanged units.

Some builders have suggested treating them as “innie” windows — cutting the old foam back to the flange and tying the new WRB into the opening, then building extension bucks for the new siding plane.

My questions:

1. For this type of retrofit, would ZIP-R be a good choice or would a separate WRB + exterior insulation assembly be more robust?

2. Is it realistic to integrate existing flanged windows into a new exterior insulation/WRB assembly, or is removing and reinstalling them the better long-term approach? My feeling is no and I should be pulling the windows and doors.

My priorities are durability and good water management in a wet coastal climate.

Thanks for your thoughts and time!