I just bought a house in New Hampshire where the previous owner had started finishing the garage built with 2x4 walls using R-19 insulation. He stuffed it in there pretty well and stapled it down, but it bulges like crazy and is ripping free in spots. He did not add the vapor barrier or drywall/plywood over it. I know he should have used R-13 insulation for the correct fit.
My question is, which is better R-13 insulation or R-19 insulation that has been compressed 2" further than it should have been? I'm trying to decide if I should remove all the R-19 and replace with R-13 or just finish the wall leaving the compressed R-19 in place and save the money. I know I'm not getting R-19, but is the compressed R-19 just as good or slightly better than regular R-13? It's a two car garage and would save me probably a few hundred dollars if I can leave the R-19 in place.