Footer question

In 2 weeks I will be starting the actual build of my ICF house in SE Tenn. All excavation is done of the drive out basement except for the footers. Soil is red clay, no rocks but the clay sure is hard. House will be 2 floors of ICF 6" block with rebar both ways.
I'm planning on a 12"DX24"W footer.
My question [s] are,
What should my footer depth be?
Would pouring the slab and footers at the same time be benificial? I like the idea of working on concrete better than rocks or red clay. Will make the supports easier to attach to.
I've read about wet setting the first course, filling and pouring the slab to it before continueing up but that seems to be more for the pros.
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I would ask locally. I can only tell you how they do it around here. And, some people will undoubtably tell you how you should hire an engineering firm to draw up a 40 page set of prints. An any rate, here's my two cents:
Combining the slab and the footers is done (google "mat slab") though it isn't typical. I don't like it for several reasons: The main reason is, in clay, in the event of rain (we get a lot of thunderstorms around here) , you have a huge mess. We like to pour our footers virtually immediately after excavating to avoid this. If you have to fart around with prepping and pouring a slab, you are extending the window of exposure. Sounds like this may not be a factor in your case? Also, the footing should be poured on undisturbed soil, and the slab should be on granular fill. The cold joint between the wall and the slab seems like a recipe for a leak. Basically, you are putting this joint right at the top of slab. At least if this cold joint is below the level of the top of slab, you have another line of defense. Also, you will need to brace the ICF's to the inside--if you have your slab there, you will have to drill into it to.
Our footings are 24" X 8".
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Footing depth is 1 ft. below undisturbed ground surface and below the frost line (as determined by your local building department.) Also remember to check as to what seismic zone your in. Zones D0 - D2 will require reinforcement within the footer and between the footer and slab (also for stem walls as well).

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