Currently my garage is 28' x 32' x 10'. I have R-13 in the walls. ceiling is trusses. I installed 3 1/2' in bottom of truss then put 9" the other way. This gives me a R-41 in the ceiling. Going to heat a additional area of 12' x 20' will use 3-1/2" in walls and thinking of using blue board for...