Good Day from rural west central WI.

[Top of the Hill Farm]

After several years of thinking about it, I’ve started my build.
There’s a little over 200 acres here on the farm.
I have about 100 acres of hardwood available to fire up the oven.
The remainder acres are tillable farm ground and pasture.
The plan is to build a 42” oven.
I have a few questions before I get started on my build.
I live in west central WI, so I need footings.
This past summer, I built a stone retaining wall with crushed stone footings that go down 4’.
My concern is that if I dig conventional footings for the pizza oven too close to the stone wall, the wall will cave in.
Refer to the attachments. I cut the existing slab where the flags are so I have enough room for the piers.
After cutting out the existing concrete, I drilled five 18” diameter holes 4’ deep. One hole in the middle, and a hole at each corner.
I poured 8” of concrete in the bottom of each hole as a footing.
Then, my plan is to use 12” Sonotubes.
The next step is to form out the base slab that will be poured on top of the piers.
After which, I can lay the blocks that will support the slab for the oven.
Questions I have at this point:
1) Are 12” diameter piers enough?
2) I assume I can pour the piers and slab at the same time, tie the pier rebar into the slab rebar?
3) When building the rebar framework, would welding the rebar make it stronger than wire tie?
4) How thick should this base slab be?
5) Should I put 2” thick insulating foam board down before pouring the piers and base slab?
My search for information about this type of footings\piers to support the oven slab, didn’t reveal much.
I would greatly appreciate any suggestions, recommendations, ideas, or links that would direct me in the correct direction.
Thank you

[Giovanni Rossi]

As stated before, not a pro or expert, but I did a lot of research on this for my build. I think what you have is fine considering you can't excavate. The bottom of the concrete piers will be below your frost line and they all live in the small footprint of the stand. The site should get reasonable drainage considering the proximity to the crushed stone under the wall. The recommendation is to not let the rebar contact the soil at the bottom of the hole, but you've managed that with the footings. Yes, put a 90 on the bars going in the holes and tie them to the grid in the slab. Remember to leave 3" of concrete between any part of the rebar and the soil.

I worked in a rebar plant for a couple years and certainly saw a lot of welded cages and baskets for both building and road construction. I always thought that was done to improve the strength of the assembly and to make installation more efficient. I wouldn't think welding would have much of a benefit in this small application. I'm sure others on the site will chime in if they believe otherwise.

12" tubes was a sound decision. Heck, they cover a significant part of the slab area. Yes, pour the tubes and the slab in a single pour.

I wouldn't put foam board under the slab, but you could run a piece the thickness of the slab around the outside where it meets the soil. You'll also want to put some expansion joint material where the new slab meets the old. I would put 6" of compacted drainage gravel under the slab and put some heavy plastic over that for a moisture barrier...tho not quite sure it will be 100% effective since you'll need cutouts for the tubes??

Slab thickness? I aimed for 6" and probably ended up around 7". Not sure what the minimum should be. Maybe someone else will weigh in. With all the weight of the stand, suspended slab and the oven, I don't think I'd go less than 5". I had to order a minimum of 1 cu yd of redi-mix and I had about a wheelbarrow extra. I think my slab was around 7'x7' and I filled 2 10" Sonotubes. Check out my build. The calculations are pretty simple if you also have a minimum delivery. No such problem if you're mixing your own.

Good luck!

[Top of the Hill Farm]

Thank you for your reply Giovanni. That helps a lot. I have experience in welding/fabrication and woodworking, but not working with concrete.I hope to pour the tubes and pad within the next week. It's been very hot and humid here lately. Thanks for sharing your post. There's a lot of good information there.