Patio question.. Overkill or not?

[lmelso]

My home is 11 mos. old. My plan: a 16d x 25w patio off the back of my house. We are in Quakertown, PA., clay soil lots of shale, 36" frost line. The house sits on 10" thick by 9' high poured concrete walls. The excavation area for the foundation was about 4 feet wider than the foundation, so there's a good amount of backfill. I've had 3 contractors for estimates and all say to rebar into foundation of house: drill in 3", w/ 1/2" rebar spaced every 2' , running out 3'. My problem is when the backfill settles, the first 4' under the patio will be basically unsupported. They say it won't matter b/c it will be rebarred into the house, plus the settlement will be minimal b/c the builder used a vibratory roller to compact the backfill, but I have no idea if this is true. In the 11 mo. we've been here, there has been lots of rain and snow and I DON'T see any significant settlement. One guy on the internet told me to auger down and use concrete sonotubes as a foundation every 6' o.c. and 3' deep. (think of a table w/ 15 legs under it), plus rebar the patio every 2' each direction, along with dropping some into the piers. This sounds like overkill to me but what does anybody here think? What the contractors want to do here is use a 4" bed of gravel, wire mesh, 3500psi conc. 4" thick, and rebar the patio to the house out 3'. Except one guy told me he uses fiber mesh instead of wwm. They are very confident that settlement wont be a problem, and slab on grade will be fine. If anyone wants to touch this question with a 10' pole I'd appreciate it. Thank you! -Len

[Rich]

I wouldn't say it's overkill to do the sonotubes. The home I am building right now has over 200 caissons (piers) under it. With over 2000lf of grade beams. So 15 legs - not a big deal :). But honestly a 3' post hole would work just as good. The nice thing about the sonotubes is that you don't have to rely on just the surface of the ground to hold anything up. The piers will do all the work by way of friction.
None of the solutions will guarantee that the patio will not pull away from the foundation or crack. They will only prevent it to the greatest extent possible.
The structural "hanging" slab will probably be the easiest but I've seen it crack where the rebar goes into the foundation. The reason being that one end of the rebar isn't moving and while the new slab is curing (expanding, contracting) it's moving. At that time the concrete is not near what it's strength should be - therefore cracking.
I know that didn't you a definite answer - but the best I could come up with.

[mfinley919]

Why wouldn't someone do the slab as stated here but not attach it to the house? Just let the slab float separate from the house? Just curious? It is just against code to start with? I know an addition would need to be anchored into the existing foundation, but a patio?

[Rich]

It's totally feasible to have it floating seperate from the house. That's why I recommended not doing it because I've seen it crack at the rebar dowels.

[lmelso]

I know it sounds like a bad idea, but if it's not done, the patio could possibly tilt toward the house as the backfill settles. At least that's why the contractors that I've talked to do it. This very problem is the reason why I posted my question in the first place. So.. what options do I have?

[mfinley919]

The back fill to your house has been there for 11 months? Is that correct? It has already gone through a complete calendar cycle of freeze thaw?

How long do you think it will take for the majority of settling to occur? I was under the impression that you were wanting to do this after just a few weeks after the back fill had been completed.

I think 11 months is plenty of time for the majority of settlement to occur.