I had my home plans drawn up by an architech, and he has in the foundation plans "contractor to field determine footings on site". This will be 2 story, 6" core. So I have one engineer telling me it has to have a footing twice as wide as the wall(slab on grade), and another who states that I can go monolithic, to keep the foam 6" above finish dirt grade. This referring to IRC320 for Florida, appling what they have learned. I live in Central Georgia with heavy clay soil. I am looking for opinions on which would be the preferred building method. Im thinking each have their pros and cons, but I just unsure.

Is the heavy clay soil the expansive type?  That is, will it expand and contract enough to crack a footer or slab?  Do you plan to have a slab or crawl space?

What type of footer did other homes in the area use?  Did they replace the clay soil with sand or gravel?

In most cases, local foundation contractors will be able to advise you.  If you can not base your decision on previous experience in the area, then you may need to ask a geotechnical engineer.

Other homes in the area use both types, ICF wise I can only find 2, both footer with a crawl space. My plans call for a slab, which is what I want. I guess my question was do I try and keep the block out of the dirt as much as possible to avoid issues with termites with a monolithic slab, or use a footer and stack my block. Both using other preventative measure, treating prior to pour and termite shields, wall coverings etc.

If you have a weak soil surface layer that you don't want to remove, you might choose a footing over monolithic (+ foam for a FPSF if required). Anyone have any other reasons not to save the expense of a footing?

The width of the footing is often determined by the width of the bucket on the backhoe doing the digging. 24" is pretty common around here.

Posted By arkie6 on 05 Jun 2011 11:44 PM
The width of the footing is often determined by the width of the bucket on the backhoe doing the digging. 24" is pretty common around here.

Another rule of thumb design criteria in my book. Makes sense if the footing is formed by the excavation and not by form boards. But footings really need to be sized properly for each job, especially if you have a two or three story high wall sitting on it. When I did my house the 13' high, 6" wall, plus the gable wall and a portion of the live and dead roof and floor loads, at one end, was heavy enough that for a soil loading of 2000 psf I had to have an  16" wide footing. If the wall had been three stories the footer could easily have needed to be 32" to 36" wide. In fact, in a couple of areas where there were corners and/or roof changes, the point load down at the footer level dictated a footer block 32" square.

Because of the weight of the concrete in an ICF wall, you can't ignore the soil load bearing capacity and the total building weight in determining footer width.

This is the foundation system we use when building ICF Passive Houses, it may be of interest.

I see FPSF, but not much bearing area (ie, not monolithic or a substantial footing).

There have been several ICF monopours with a trench footing. Take a look at the attachment.

I like it - if I interpret it correctly, it includes a slab? How well does it work practically?

That drawing specifically does not include the slab. The slab would be poured at a later date.
If a slab was wanted; the bracing would be placed on the outside of the wall, the foam would be trimmed up 4" on the inside, and extended set screws would be used.
There are about 4 jobs right now using this system. I will put some photos up once I have received them. In theory it should work like a hot dam.

Here is the attachment on monopouring the slab, footing, and wall with a horizontal ICF