Our family lives in Vermont and recently bought and dismantled a 24’x30′ one story timber frame house built in the in the mid 2000’s.  We are moving it to our land and milling out timbers to make it 24’x40′.  It was orginally on a slab but we plan on building a walkout basement with one full foundation wall on the north side, pony walls or whatever a half foundation wall that transitions to a full stud wall about half way to 2/3 of the east and west wall.  The south side will be a fully framed wall.  The basement area will be our master bedroom/bath, a laundry, kids bedroom and kid area.  Upstairs will be mostly open kitchen, dinning and living room with a bathroom and kids bedroom.

Before we started excavating  we knew there would be a chance of hitting ledge on the southside of the house.  There is some exposed 10-20ft away from the house site.  We ended up finding ledge mostly on the south east side that covers most of where the foundation wall will site and along 3/4ths of the south wall.  The north wall i has plenty of depth for a footing and full size wall.  The south east corner roughly a 8’x10′ area is 2′ lower then the ledge.

We are planning on putting foam under and around the foundation.  I’m wondering the best interface for the ledge footing interface.  And maybe having to drop a stem wall where the ledge falls off.  Is there a best practice for filling in that low spot?

Any help would be great as I wanted to get some ideas before I started talking to concrete contractors.