I have read through your articles and watched the videos on using polyiso for exterior sheathing and insulation. After spending quite a bit of time researching this issue, I would like to know your comments on the following.

I live in the Seattle area and have spoken to a company in Portland with a similar weather environment about the best way to accomplish the above. They recommended using polyiso 1 1/2″ over my existing 1/2″ CDX sheathing on the exterior (I am doing a remodel with new siding) by Hunter (no foil or material on it) followed by a housewrap for a water barrier.

They claim their research shows any dew point to fall withing the polyiso outside of the sheathing and recommend the housewrap to allow moisture to escape, but as a rainshield. My siding is 1/2″ T&G cedar, but it will be vertical oriented, so the furring strips will have to be horizontal. I would like to have space behind for air movement.

Your video shows placing plywood around the interior of the framing for the windows which helps with taping the edges for polyiso boards to seal that edge. The Andersen windows I am considering purchasing have a 1-3/8″ flange setback. It seems to me that I would need to fur around the window opening to allow for attaching the flange.

Also, since the T&G siding is vertical, the strips would need to be horizontal to place the siding. Any problems with that as water trapped behind would catch on the strips rather than free flowing down to the ground? Probably would need some drain slots.

Is this a viable plan or do you disagree with the application in this scenario? I apologize for such a lengthy inquiry, but several details are needed to install properly.

Thank you for you comments.
Sincerely,
Steve Dorsey