We have a 22 x 22 exposed basement with a 22 x 44 ranch house build on top. It extends 22 foot off the basement and is supported by 2 beams and six posts sunk into the ground. Photos on the web site: www.angelfire.com/falcon/adessa. We would like to build under this existing structure and need to know how to support the upstairs so it doesn't fall in the process of putting in the new foundation and building up the walls.
That is, actually, a job for a professional. It can be done, though. The house that cantilevers off the foundation will have to be supported by beams and cribbing located outside the footprint of the structure, leaving access for excavation equipment to dig around and then under the unsupported part of the house. Your probably looking at a job that requires not only the normal trades (excavation, forming, concrete, etc.) but also one with house moving experience, as he'll have the equipment and expertise to evaluate the structure and then place the temporary supports where they'll support the house but not be in the way of the excavator.