"J. Clarke" wrote The sheetrock per se doesn't have much R value, but it serves to seal the inner surface of the wall, thus creates a closed air cavity in which convention is suppressed by the fiberglass, so by not using it you may lose more than you would expect just from the R value of the sheetrock.
It's interesting you should say that. It's been explained to me that in fire-resistant safes, such as gun safes, that several layers of sheetrock are used to protect the interior of the unit.
Now, exactly what kind of sheetrock it is, I have no idea. Don't even know if it's true.
If it were my garage I'd insulate it AND sheetrock it all the way around using a double layer of sheetrock between the garage and the dwelling for fire retardation. As I recall it's required in Callyfornee.
My garage is NOT insulated but is finished on all the walls and ceiling with masonite type siding. It's colder than a witche's tit out there right now. I wish it was heated and insulated. Maybe someday we'll pull it down and do just that.