JFYI, through the 50s and 60s we built to two standards, for most homes we built a monolithic pour for garages, for anyone who was getting a FHA loan we built a stem wall around the garage and recessed a slab later at least 6" below floor level. To this day I still put vents around the garage, a few years ago I had an inspector ask why I did that? Heaters, water heaters, and gas dryers were always raised up on platforms at least 18" above the garage floor.
On another subject but related, last week Berkeley passed an ordinance banning gas lines into all new buildings.
BTW, on homes built for FHA loans we had two inspections, local and Federal, I remember a retaining wall that passed local, then the FHA inspector made us tear it down and rebuild it, then the local inspector made us tear it down again and rebuild it his way.