Seems like there are some experienced foundation contractors with business in MN/WI here who would be willing to share some advice.

I’m building an addition onto a cabin in SE Minnesota (Fillmore County).  The 24X20 cabin is built on treated posts and beams, with all 5X4 posts dug down to a layer of limestone 38″ – 42″ below grade, and backfilled with gravel.  Floor platform out of 2X8s with OSB on the bottom and 3/4″ T&G ply for subfloor. FG insulation in the joist spaces. Been there for 5 years with no signs of heaving or settling.  Sloping site, grade drops about 4′ in 20.

The addition(s) will be three wings, 20X24, 34X14, and 10X22, surrounding the existing cabin on three sides.  Excavation sub who also put in the 6 foot deep water line trenches and septic drain field says OK to removing silt/clay topsoil down to the limestone and pour footings OR place 6- 8″ compacted gravel for PTW crawl space foundation directly on the limestone. The foundation will be designed and installed by a pro who has done many wood basements in this area…some stretching back 25 years, and this will be done with consideration for loading and drainage with an engineered back-fill, vapor barrier and probable rat slab in the crawl space.

Do you think I’ll be risking uneven frost action between the cabin and additions, considering that this will be a somewhat unusual excavation and foundation?

Would appreciate your input on this before I plunge ahead.