I am in the middle of a renovation of our older farmhouse that has had bit and pieces upgraded over the years. One sections(maybe 1000 square feet of wall area) we are adding a porch to and changing opening for new windows. This section is the worst insulated with just rough sawn true dimension 2×4’s filled with blown in cellulose many years ago. The siding is poor condition pine clapboards, then 1″ board sheathing, 4″ of cellulose, lath, plaster, then newer sheetrock in good condition keeping the plaster in place. The interior of these areas we plan to not touch other than some tweaks for window openings. 

We are in climate zone 6 plan with these exterior walls was to remove the siding and then (2) layers of 2″ foam for proper dew point protection, rain screen, then new siding. However a local builder friend said why don’t you just remove the existing sheathing, horizontal strap it like a Mooney wall, have it closed cell spray foamed, then sheath it with 1/2″ CDX. This would allow the spray foam folks to get 4″ or more in most of the wall and then 1″ or so on surfaces where the Mooney style strapping would not touch the  outside face of the studs. Basically reducing the thermal bridging a lot!  It would also mean my walls would not get much thicker and allow for easy window installs, etc.

Does my idea make sense?

I have seen some examples of this with cellulose and something like a Larsen truss that is deep, but nothing like this. 

Any ideas or thoughts would be great! 

Thanks!