As I keep building my "dream house" in my head I keep running into problems!  All is well and understood above the sub floor.  But getting from the footings to the top of the floor framing either adds thermal bridges or requires separate footings.
I choose not to go to the extreme of double footings.  Now the problem becomes how to economically, both thermally and monetarily support the outer wall.  The most logical place for insulation of the foundation is it's exterior this strongly favors making the inner wall load bearing.  For a single footing under the inner wall, the floor system must, somehow, cantilever to support the outer wall.  The obvious method is to use the floor's structural members and place the " rim board" under the outer wall, not very economical either thermally or monetarily.  What are the alternatives?  The best I've visualized is a "Larsen truss" pony wall with the rim board as it's inner sheathing.  Any others?  The easiest way I see to build it is use lengths of thin web " i joist" , flanges ruining vertically, cut the same length as the width of the rim board. After the rim board is in place add an I joist section outside each floor framing member using  screws through the inner flanges into the rim board.  If the costs, in heat loss and $ are tolerable, the sub floor can now extend under the outer wall.

There are ways; I've seen several at recent conferences, and you can find lots of examples on the various websites. More importantly though is that you appear to be overthinking the problem. A double wall sitting on a concrete foundation where the rim joist and sill is insulated on the interior with a few inches of spray foam is pretty well thermally isolated except for the floor joists and the plywood underlaymemt, for example. If you use TJI's, the amount of mass extending through the thermal bridge is minimal and more important, it works. The bridge does not have to be perfect, it has to be minimized.

Bob,
I want the exterior of the double wall to have it's exterior face directly above the insulation on the foundation's outer face so that above grade portions of the foundation can be clad with the same material as the foundation. I am not using TJI floor members but instead open web trusses. What I'm suggesting is to use a TJI as the stud in a pony wall that has no top or bottom plates with it's lower inner flange end end sitting on the same mud sill as the rim board and floor truss end. The sub floor can be a rather substantial thermal bridge and extend over the entire pony wall making erection of the outer wall above straight forward. Or the sub floor's thermal bridge can be eliminated if it only covers the inner flange of the vertical TJI. The second makes the outer wall's studs a bit longer, by the sub floor thickness, and makes it's erection over the top of TJI, hanging by their webs ,a bit tricky.  I lean toward the extended sub floor because it simplify s building the walls and adds a tremendous amount of stability to the outer wall in the horizontal plane.

So the PT sill will extend beyond the foundation over the insulation? I've used this detail extensively in the past and have seen since that, over time the PT will move and cup and warp over time, potentially leaving gaps, so plan for that.

I asked several experts at the last conference directly about my concern about the termite/carpenter ant/rodent infestation issue reguarding exterior insualtion (which I have used extensively). (Since so many new designs have that feature) i was hoping to hear that if I did or used XYZ it should not be a concern. No one would say that. What they -all - did say - in seperate discussions - was that they are valid concerns and to go from there.

Bob,
     I do not see the PT mud sill as needing to overhang concrete.  I think that would be undesirable.  Tentatively I have 5" exterior Roxul and 8" concrete basement walls with a PT 2x8 on them.  

I calculated how much insulation I would need to add inside the rim board to cancel the thermal loss through a 3/4" sub floor extending to the outer wall's outer stud face with my planned insulation (Roxul comfort bat).  Surprisingly it only takes r 2.3.  It is most definitely worth while to have the sub floor continue over the entire pony wall.  BTW using 9 1/2" TJI 100C for the pony wall studs, 1/2" plywood for the rim board, 1/2" fiberboard exterior sheathing, 1/4" XPS (Greenguard DC14) with 9 1/2" Roxul comfort bat (r 15+r24=r42) a 14" high rim calculates as r 43.4  with 24" OC joist.

what is under the TJI preventing the insulation from leaking out and keeping the critters out of the wall?

Bob,
A detail to be worked out! The insulation being bats is not an issue. Thank you for pointing it out!  Metal will be a huge thermal bridge but definitely keep the critters out. One quick thought of a "critter blocker" might be a strip of fiber reinforced plastic, like "Structoglass" covering both the foundation and it's insulation. This adds an air sealing challenge under the 'mudsill'

Bob,
     You were right I'm making a simple problem complicated!  I looked at a dramatically simplified solution.  My floor truss will be " Trimjoist".  They have a 1 ft section on each end that is an I with 1 1/2x 3 1/2 flanges and a 23/32 web.  my alternate solution is simply extend the trim joist all the way under the outer wall eliminate the band joist but use soilid blocking made of 3/4" OSB between all the joist s .  If I move the blocking to leave 10 1/2" for insulation I can fill it with r 45.  With wood @ r 1.25/" and 3/4 blocking,  my fiber board sheathing and XPS drainage plane the thermal resistance of the " thermal bridge" is r 16.6 and the cavity thermal resistance is 48.24  The average r value is r 43.6 with joist  24"OC.  Accounting for the thermal bridge of the sub floor reduces the average r to 39.9.  With enough spray foam to assure a proper air seal I exceed my r 40 goal. 

How about building an 8" concrete block wall with a 12" block sitting on top of the last row cantilevered to the outside. The floor truss sitting on 8" of the block with the outer wall sitting down and on the outside edge. The outer wall insulation would cover the ends of the floor truss and rim joist.

"How about building an 8" concrete block wall with a 12" block sitting on top of the last row cantilevered to the outside. The floor truss sitting on 8" of the block with the outer wall sitting down and on the outside edge. The outer wall insulation would cover the ends of the floor truss and rim joist."

As I understand this suggestion, It adds a 4" x8" cross section segment of block @ r1 atop an insulated wall in the basement replacing r 15 of insulation only to complicate the construction of the upper walls by making them different heights and requiring that the outer wall be dropped off the edge of the floor deck to be erected. In addition the shrinkage of the two upper walls is no longer close as the inner has floor joist and the outer doesn't. Certainly no better thermally, it does give a continuous rim board rather than blocking. Is there an advantage I'm not seeing?

Edit: I wrote the above assuming this thread contained my current thinking IT DOES NOT  My answer to BOB is close but I'll end the sub floor at the outer surface of the inner wall making the outer wall taller, by the thickness of the sub floor and eliminating the subfloor as a "thermal bridge".

I was thinking the outer wall would be below the floor deck thus allowing for continuous insulation. I envision 4" of sheet foam attached to the outer concrete block wall terminating underneath the cantilevered block. This would make both walls flush with each other.

"I was thinking the outer wall would be below the floor deck thus allowing for continuous insulation. I envision 4" of sheet foam attached to the outer concrete block wall terminating underneath the cantilevered block. This would make both walls flush with each other."

Are you are now saying there is NO insulation outside the cantilevered block?
Any way, cantilever floor joist or trusses, with blocking under the inner wall, no classic rim board and insulation between them equal to the walls above Are OK thermally, simple to build and have desirable shrinkage attributes.
Three layers of r 15 Roxul comfort bats in the double walls and the floor joist gives r40+ from below the floor up (with 24" OC framing).