concrete slab

using your words

foundations are not poured on top of patio's.

With out a LOT more SPECIFIC information , can not see it from here

what do you mean by slab foundation? foundation for what? what condition is the conrete patio in? we need more information.

Step one. Follow the code

Step two, if you don't like the code, see step #1.

I don't know about you, but I would want to know a lot more about what is under that patio slab before I used it as any part of a foundation for anything more than a dog house.

Does not matter what I think. If the inspector thinks different, you have a problem. Run it by him first. If the slab is for a 10 x 8 shed and no permits and inspection required, you may be OK. Otherwise, it will be very expensive to tear out if the inspector does not buy it.

Let me guess, your code is for a new foundation? Break up the patio an build a "slab foundation", or contact the permit department for some clarity.

Oren

"My doctor says I have a malformed public-duty gland and a natural deficiency in moral fiber, and that I am therefore excused from saving Universes."

is this for a patio or are you building a room addition. if it is a room addition you better check with your building regs. i did that, i had footers under the existing slab. i will bet if it is just 4 inches you do not have footers.