Anyplace you build a wall on the slab you need footings. Ditto on gravel under the slab, it allows drainage while maintaining hydro-static pressure under the slab. The slab won't sag.
I've been involve building a two story three car garage on my last property with an apartment up stairs. Also, two story a six car garage, three on top and three on the bottom, on the side of a hill. Yes a three car suspended garage on top with twelve foot high doors for construction equipment and lifts. Lots of steel, corrugated metal and concrete. Full disclosure, many summers when my business is slow I help my brother build McMansions. Lots of suspended garages over basements.
I would advise just drive through a new neighborhood under construction and see how they do it in your area.
You might consult the concrete finisher on whether to spray "cure" on the surface if you decide on epoxy paint. The "cure" is basically like a lacquer, you may have to strip and sand it for a good epoxy application.
The coolest garage floors I've ever seen were at European Car in Wichita Kansas, a BMW dealership. The floor was brick size terracotta tiles, no mortar, just laid very very very tight. You could eat off of them they were so clean. Frito-Lay factories have the same floors.
Last edited by MACMC; 08/02/2019 10:56 AM.
