Exxterior wall improvement....

[mrcaptainbob]

The 30x30 house addition is close to fifty years old by our estimation. It is, from interior to exterior: knotty pine verticals above wainscotting with horizontal below, followed by pink fiberglass insulation, followed by Celotex fiberboard, followed by vertical cedar board and batten siding. The insulation is very poor condition. The Celotex has been compromised, as has been the boards, by woodpeckers of the years. There are many, many air leaks.
The plan is to remove the board and batten, all of the messed up Celotex, and remove the poor insulation. This leaves only the knotty pine interior boards. New insulation is the first, of coarse. But that's where my dilemma is at. Go with 3.5" fiberglass? (not a fan of it, ... how do I secure it properly? Ideally it should be flange stapled to the studs. Can't do that in this situation.) 2nd option is to spray foam. I really, REALLY like that idea. But....the closed cell spray foam claims an R value of 7/inch. Preferred wall insulation in Michigan is minimum R19. Rolled fiberglass is R13, batts is R15. So....2" of spray foam should equal R14. But...it will be airproof. So, should I fill the studs level to their surfaces, there by giving an R value of 24.5? Would one inch of foam at R7 be equivalent to ?x of any other insulation?
The remaining plan is to then cover with 7/16 OSB, followed a Tyvek type material, followed by vinyl siding.

Any opinions or suggestions?

[adnadeau]

There are several issues to consider here: air leaks, R-value, type of insulation. I believe the spray foam is probably the best insulation. I don't believe you can get it applied to less than the full thickness (3.5" ?) of the wall studs. Some of the videos I've seen show the excess is scraped off level with the studs after a few days of drying. This stuff is normally applied by some company with the proper equipment. The technician is encased in a Tyvek suit with an external air supply.

If you go with the spray foam it will be airproof, as you say. You had air infiltration before with the fiberglass insulation. If you spray foam the entire house, you will most likely have to install a mechanical air exchanger such as those made by Venmar. Without normal air infiltration, any inside moisture created by bathing, cooking, breathing has no place to go and will condense on the windows.

[mrcaptainbob]

Thanks for the quick response, Adnadeau. Air exchange in this old house won't be an issue. The main house is a two story brick, circa 1863. Not the best insulated. Although not air tight, it's far better than the board/batten addition. My wife tried having candles in the living room, only to have them actually blow out on windy days! This is the year to repair that and a few other issues. The addition was a great idea and a great design, just poorly applied. I think I'll be going with the spray foam. Yes, I have seen programs on how the foam is cut smooth to the stud surface. I really like the idea.