Here's an example of what you might be looking to do. Notice in the first photo that the wall was frozen with moisture. I used heat gun to transpire the moisture away. I placed R10 2" thick closed cell foam with proper (like packing tape) at the seams held up with an adhesive especially made for foam board. Then, I stud the wall and placed temporary jigs to pressure the foam board equally against the wall until the glue dried. Then, I put a r13 in the 2x4 wall and covered it with 1/2 GWB. This is a fairly expensive project material wise. The 2x8 sheets of DOW are not cheap...nor is the fiberglass bats...