I am having a hard time deciding on my insulation approach to my new home. I have a chance to buy some Poly-Iso 3.5 inch foam or 2 inch foam DIRT CHEAP...like HALF price for brand new foam. Trouble is, I am not confident that this is the right approach for my location and climate region. I am very concerned with getting it wrong and creating problems with moisture in my walls which leads to larger problems like mold and rot. I have an allergy/asthma issue with my daughter and myself. Air quality is a must. I have asked this question before and received mixed answers. I wonder if I am able to just air seal the stud cavity with closed cell flash and batt type scenario that I might actually be able to get some decent performance out of my 2x6 framed walls.....please advise. We have already broken ground and our budget doesn't allow a ton of room here for extras. Adding furring strips, extra 1x material for around windows and several trips around the house for sheathing, then foam, then tape, then window boxes, then windows...is really really hurting the bottom line number on my build.

What city and state?

Ellettsville, Indiana 47460

Do it!!! We had our house resided when our addition was put on and I didnt know this was an option. I have a double studded wall going up in the addition but the rest of the house still has 2x4 construction with old 1/2 foam instead of plywood. Even if I go back and put 4 inches of foam in there will still be thermal bridging at the windows and such. Dont skimp on this. Extra R value never hurts. We would have spent maybe an extra $2000 - $5000 and easily had R20-R30 walls in the whole house if not more. Now I have to rip out drywall one room at a time and spray in open cell and possibly furr out the wall on the inside.