Add foam board to outside of existing walls.

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Replies
Part of the answer depends on where ya are--where are ya?
Southeast Michigan. Brighton
Hi driopel
I think that the thickness you have to use to make it work properly depends on where you live (temp). I just talked to a contractor friend who did a reno just like you discribed with 2 inch foam. I know that here (coastal BC) they recomend 1-1/2" to 2". I have no idea what your climate is but I would imagin that it is colder there so thicker foam would be needed to avoid the condensation problems in the wall.
If you eliminate the 2x2s in your proposal you will would have far less thermal bridging which is one of the main advantages to adding foam on the outside. My friend hung the vinyl back on with three inch roofing nails right through the foam said it worked great.
There is some discussion about where to put the moisture barrier in the green building adviser web site.
I am interested in doing this here on our next new build,
Angus