Pompeii Foundation

[Chach]

Hi,

I have been thinking about building an outdoor fireplace along with an outdoor kitchen and pizza oven for some years now. These last few weeks I pulled the trigger on ordering all my supplies and now I'm ready for the foundation. I tend to overkill anything I make as I am in the trades and I have many professionals I can rely on except for concrete. I was thinking about the foundation for everything including my fireplace and Pizza oven as I will be pouring these together. In Chicago we get some below freezing temperatures and in my area our frost line is 42" I thought a lot about this foundation as I don't want to build something like this and have it fail. I was thinking of 12" piers in each corner of the oven and fireplace down 42" with rebar in the tube and tied into the rebarred slab and a monolithic pour with a pad 6" thick. I then talked to a landscape contractor who does these sort of builds and offers a 5 year warranty on his work and he said this is way overkill. He said 6" stone with an 8" pour is way more than sufficient for this. I came up with 8" crushed compact stone and utilizing a 2x10 as a form so I have 9 1/4" of concrete. So I will be excavating 17" for this build. I'm thinking I'm ok with this thick pad and aggregate underneath but I just wanted to hear some thoughts. I know this has been brought up many times on this forum but I'm starting this thread again. Thanks in advance

[rwiegand]

I think your contractor has it about right. If you want to overdo it I'd err on the side of making the gravel base deeper rather than thicker concrete, and ensuring good drainage under the slab. If you really want to be sure it never, ever moves then a perimeter foundation to below frostline is the way to go--but that would be really serious overkill. I have a 6" pad on about 8" of stone. It hasn't moved through four MA winters yet, I'm just about to begin building on top of it.

[purplehaze]

Chach, I overbuilt my oven and base also and live on the east coast. I built mine on a slope and didn't dig down too far, just enough to get rid of the top soil. I used about 6" of cement sand, rocks, and old bricks under the slab. I added rebar and poured about a 5" concrete. The mason I spoke with said that the base may move a bit but it would move as one large piece so as not to compromise the oven structure. He also added that I could have put a layer of hard board insulation under the slab but that it was not necessary. After 2 1/2 years I have no issues with the oven foundation or structure. Just my 2cents.
Good luck