"Jason Wagner" wrote in message
...
From what I have been told, the older part of the house basically needs to
be gutted (all interior walls and existing flooring removed) and then the
new foundation gets poured. Then the walls go back up.

A good friend recently added not just new foundations, but an entire
basement under his house with less trouble than that. Basically the process
was to construct some shallow footings outboard of the house, then jack up
the house until it was bearing solely on the temporary footings. Then, a
loader excavated completely under the house, new basement foundations &
walls were installed, and the house was lowered back down to bear on the new
construction. Frankly, I didn't believe it was going to work, but he's very
happy with the result.

FWIW,
Joe F.