[kach22i]

I designed a two car garage with an elevated slab once (sloping site). The sub-contractor was complaining about how much re-bar my structural engineer put in there and that I had re-bar in spots "doing nothing". I held to the design despite his claims that he had gotten away with half as much re-bar on other projects.

Years later a builder client of mine purchased a house with a detached (elevated slab) garage. First thing I asked was, did he build it and how his elevated slab was holding up. He said; funny you should ask, first thing we had to do when we bought the house was raise up the garage and install new supporting walls and concrete floor as they were falling apart with our wood workshop in there. They ended up doubling the re-bar over what someone put in before.

I have no idea if the same contractor was involved, but it is a small world.

Having a structural engineer check the re-bar design might be a good idea. There is nothing rule of thumb or conventional about it.