footing issues for a new 2story house

[VALENT]

Building new house 2 stories 30ft deep by 50 ft wide..
I am located right out of Houston Texas and have to elevate for flood control about 3.5 feet. I am planning on a concrete footing around the outside edge of the house and down the middle |(at 15 feet) that will be 36 inches wide and 16-18 inches deep. Then i will build up above the flood elevation with concrete block and start framing from there. So here are the questions? 1 what do you'll think of this? 2 are any of these figures way off? 3. How much rebar is needed and where? Oh, by the way, I just found this forum and have been overly pleased. In fact, this is the first forum which has actually coerced me into posting.

[Rich]

1. It sounds good to me but I'm not an engineer.
2. I'm not an engineer.
3. I'm not an engineer.
Those 3 answers will probably change that last statement. Honestly it does sound like it's a good plan but without knowing soil information, exterior and interior materials, roof loads, wind loads, etc..etc.. I couldn't even make a good guess what would be required. And even if I had the information it would take a fair bit of time to come up with an answer.

[VALENT]

Thanks for the reply. I certainly do not expect any person on the forum to make engineering decisions but was asking mostly on an experience basis of others. In this area about 95% of the houses(if not more) are built on concrete slabs. However because of my need for elevation above the flood zone, I am looking at other options. This footing with a block wall seems to be the best alternative i can find.

[mjpliv]

I am assuming the larger than normal footings are for additional bearing for the soil type?

Are you using an engineered floor system? The reason I ask is that with 15' span to the center, a 2x10@16" OC floor is pretty much maxed out.

[VALENT]

I am actually waiting on the prices for the I-joists now. Otherwise, I will be using syp#2 2x12 @16oc. Actually, it is the 3 ft width of the footings that I question also. But my father-in-law and his buddy(engineer of some sort) feel that it is necessary. The soil is actually a pretty decent mix of loam and clay. There will be some shrink-swell issues but not as bad as many places. And, I must admit that the foundation is somewhere I would rather overdo than underdo.

[mjpliv]

I would hazzard a guess that the engineer involved may be attempting to build a grade beam (normally built on grade) with that size of concrete footing. A grade beam provides support in the event that bearing soils can no longer support parts of the footing due to errosion or settlement. If this is the case, the rebar size and locations should be designed by an engineer.

[VALENT]

Actually grade beam is definitely something that was said. But, unfortunately, it meant very little to me until now. Thanks for the insight.

[VALENT]

well, the footing or grade beam has been poured. The bottom of the footing is about 24 inches below grade (ranges from 20 inches at front to 28 inches in back).The concrete is 16 inches deep and 32 inches wide. We used #4 rebar in four lengths for the entire perimeter with cross pieces every 18 inches and laid this grid about 3 inches from the bottom. The next step is the concrete block wall. It will only be 4 courses high.

[Timothy Hampton]

Most of the house foundations I've done in the Houston area have consisted of poured concrete piers and grade beams. I've also done slab on grade foundations incorporating void forms and grade beams. Your design should work out ok as long as the footings are wide enough for the loamy soil. The clay soil down there is notorious for shrinking and swelling. Mudjacking is a thriving business in the area.