One thing I don't really understand with framing 1/2" away from the wall is, doesn't that mean that every 16 inches for 8 foot lengths that the insulation factor is only 1/2" (R2.5) + the 4" width of the wood stud? As opposed to 2" of insulation (R10) + the wooden stud R-value (whatever that is)?
Is 1/2" of spray foam really enough behind all of the wooden vertical frames?
I get the idea that framing first ensures the frame is sealed into the wall so no gaps but we are also reducing the amount of insulation also, correct?
Also, if I intend of putting Roxul R15 batts in the wood frame, should the framing away from the wall be 2" if I want to put R10 (2") of spray foam? I'd assume so.