I'm designing a stacked duplex, with one apartment on the main floor and another in the basement.   The basement portion of the dwelling is divided into 2 sections. One section of the basement is part of the main floor and includes a family room and garage, and the other section serves as an autonomous apartment.   The basement is 54 inches below ground level, and the finished floor to ceiling height is 9 feet.   I'd like to have a sloping driveway leading down to the garage. The slope sho