I am planning an addition to the back of my house, aprox. 28' x 32'. My current house is built on wood joists and is about 14-16" above grade. I am trying to figure out the best foundation to build with it considering my constraints. FYI, I do plan to permit it and perhaps find an engineer to do the drawings, but I'm just in the early stages and would like so opinions.

I could just pour a slab, but that would make the addition drop down, which I don't want. A raised slab seems out of the question, because I have limited backyard access (no alley) so, bringing in all that fill would be a lot to do. And concrete is so expensive now, plus I like the ability to cange thins with wood floors.

So, to build on wood, seems like the solution. But, with only 14"-16" above grade it doesn't seem like I could build a stem wall 6" above grade (the requirement here) and still have room for joists (unless I used 2x8, but I'd rather use 12" or TJI). Plus I would need to excavate under the joists to give me 18", and putting that dirt around the back yard is going to raise my grade level.

A builder friend of mine suggested doing something like this, (I will try to attach a jpg.) Build a stem wall all the way up to floor height for your walls (in my case 14") and build an interior ledge for your 12" joists. Then, when you go to excavate, your stem walls are so far above grade it doesn't matter if you raise the ground level much.

Help! What seems like the best solution given these circumstances.

Thanks, Jesse