Pizza Oven Planning - Foundation And Our Drywell

Over the past few years, I've dreamed about building a backyard pizza oven - both in our old house in Elmhurst and here in Downers. I've posted a few times on the potential location(s) on the blog. Here back in 2017. And, here again earlier this year and most recently just last month when I was talking about a pond. In each of those explorations, I've included a location of the pizza oven that is along the north side of our property, off of our patio, down in a lower level of our patio.

As I continue to think about the location - and I'm increasingly thinking that the northside site - that is situated down low - is the right spot.  It is low-lying, so the fireplace won't be sticking up for all of the neighbors to see - and to expose to the elements.  

I've read the Forno Bravo DIY installation instructions like six times and lurked all over the forums over the years.  One of the pieces of counsel that they give is that if you live in an area of the country where you get hard frosts, there are some additional considerations you need to take.  That includes how you would handle heaving.  Form the FornoBravo instructions:

(highlight, mine). 

They say that you would need to properly engineer the foundation to remain level.  And, for most builders, that means they do one of a couple of things:

1.  Roll the dice.  And just build on a slab.  

2.  Dig some footings and put in sonotubes at the corners and fill them with concrete.  Then they float their foundation on top of those four footings.

3.  Excavate a trench around the perimeter of your oven.  Pour in a concrete footing.  Stack block on top to get to grade.  Then pour foundation slab on top.

You can see an example of #3 here in this forums post.  Heavy excavation.  Rebar, concrete poured.  Blocks on top.  This is *the right* way to build the oven. 

It is also the most expensive and labor intensive way to build the oven.  

But, might there be another way?  The location in question turns out to be located directly on top of the drywell that we had installed as part of our house project.  The Village required us to mitigate storm water.  One of the ways was the installation of a large drywell.  Here's what the Village of Downers Grove says about Drywells:

See that typical Drywell cross-section?  That's what we have.  The bottom of which is full of large gravel and is topped with 6" to 12" of top soil.  That means, that in the area - below - I have a large gravel, well-drained base.  Here's a look at the footprint of one of our drywells:

So, now imagine building on top of that.  This article makes me think that 'gravel soil' won't heave. 

Gravel soil itself is generally considered as free from frost heaving. Therefore, it is usually used as soil base construction material in seasonally frozen regions.

I haven't dug down to see exactly where the gravel starts nor have I dug down to see how deep it really is, but I know there is a cleanout in the ground that I can peek in to and get a gauge on how deep the drywell really is in this spot. 

I'm thinking this might be a good solve: excavate the top soil to get down to the gravel base of the drywell.  Form a frame for a slab and pour it on top of the gravel base.  Build the block foundation on top of that slab and thanks to the drywell, there won't be any heaving.

Could this be the solve for #25 on my 2020 to-do list?