I have friends that built in Gladwin..Just a small little 5500 square foot cottage... ...Its beautiful and the 180 acres its on was left to them by thier rich gramps instead of giving them cash..
Anyways they built a garage under a living space and they now wish they would have made a few corrections..Insulate the heck out of the area between the garage and rooms above..Not only for fumes but if they are bedrooms above you hear freaking everything that happens in the garage when trying to sleep..We go out hunting before light and the women folk complain of the noise we make in the garage..Its a real issue in that home so take it for what it is..You have a beautiful place..!!