We currently have a walk out basement with a 12x12 concrete slab. We are looking to increase the size of that slab/patio to go underneath our deck. We are going to get the existing slab removed.

My question is, should we get a retaining wall? Where we want to end the patio doesn't drop off to much (maybe nothing more than a foot), so do we need a retaining wall? Some companies say yes and others say no.

Also what needs to go under the concrete? All companies have quoted the rebar but some companies say do not drill into our house foundation and other companies want to drill into our house foundation to attach the rebar. We live in Ohio so we have lots of climate changes throughout the year. Should we be drilling into our foundation or not?

Finally, how thick should the concrete be on top? We are looking at doing a seating wall around the outside and one company said that part of it will be on the concrete and the back part would not. He said that the part that is on the concrete would be thicker concrete at that area. I said that I was worried about the weight of the seat directly on the concrete. What are the rules about putting paver seating on top of concrete even though it's not the full weight of the seat?