We used 6' walls for the garage. This was done to minimize the number of stairs between the house and garage. It also allows us to build an "ADA" compliant ramp. The fill in the garage had to be compacted, so the slab won't crack. The concrete is only 7 days old, not nearly enough time to cure. So, on the exposed walls we added pea gravel to keep the pressure of compaction off the walls. It must have worked, no cracks in the walls.
