Buried oven in a hill

[Cgosnell3178]

So I had an idea I would like to flesh out and get opinions on if it's possible. I live in a townhouse that has 3/4 of a fairly steep hill. There is an existing retaining wall that's about 2' tall. I want to set a brick oven in the hillside that would be covered back up by dirt except for the opening and chimney. I feel that I should have a door and that it be big enough to remove ash. Thoughts?

[MarkJerling]

Assuming you could excavate the area without causing stability issues for the hillside (yes, you may need an Engineer) it should be possible to do. But, soil holds moisture, so, anything built into the ground will have greater moisture control challenges than something built above ground. Waterproofing tends to be expensive, so it may make sense to build a suitable retaining wall and then roof it over so that it looks like it's sitting in the hillside when, in fact, it's actually not. Make sure your retaining wall complies with local building codes (as I said, you may need a Structural Engineer) and consider moisture moving down the hill, both above ground and under the topsoil layer.

[Gulf]

Water intrusion is on the very top of the list of things to consider when building a wood fired oven. For an oven to perform it must be dry. Water can and will wick through masonry from the surrounding soil unless steps are taken to prevent it. Do plenty of research on this before you proceed. Below is a quick search of the site with the key words “retaining wall”. A couple of builds such as you propose may also be included in those discussions. You also may want to investigate “French drains” and “basement waterproofing” on a web search.

Some Forno Bravo discussions about ovens built into retaining walls.

[Cgosnell3178]

For clarity of the landscape, my backyard, thinking about center, just above existing retaining wall. Hill isn't super steep, you can walk up without too much difficulty.

[MarkJerling]

For clarity of the landscape, my backyard, thinking about center, just above existing retaining wall. Hill isn't super steep, you can walk up without too much difficulty.

That does not look to major! I would imagine that you could easily do a bit of excavation and have a retaining wall, complete with some sub-soil drainage behind and a small soak-hole and silt sump to handle that. You could then grow something over the retaining wall to hide it and make it look pretty.

[SableSprings]

I had the opportunity several years ago to use an old wfo buried in a hillside in Italy. As mentioned above, the moisture/water issues were obviously a big concern to me and based on the hours of firing I did, it was apparent the insulation layer had failed or was non-existent. I always thought this to be a great wfo site option, but the investment in creation of a extreme watertight insulation capsule will be high. The Italian oven had a squirrel-tail flue system but getting it anywhere close to pizza temps was a challenge and bread baking was severely limited. With my experience, if I was doing an oven in your hillside, I'd only set the back half of a doghouse style enclosure into the hillside so I could maintain a proper insulation layer above the oven and really pay attention to the base support (oven weight ) and drainage system beneath the base insulation.

I hope you do decide to build this oven as I think it could be a real show stopper! Keep us posted, it will be a worthwhile build.

[deejayoh]

Look into Xypex, a concrete additive that makes it waterproof. It is quite expensive - but works. They use it in swimming pools, concrete pipes, etc. I built my oven on top of a retaining wall, in the pacific northwest where we have plenty of moisture. I added Zypex to my base, and have had no issues in 8 years.

[Cgosnell3178]

So would an air gap work? I'm thinking basically a 3 sided retaining wall, then a 3" or so space topped with brick/stone for the upper side of the gap. We don't have much water running down the hill even in the heaviest rainfall that I've noticed in the 3 years I've lived here.

[MarkJerling]

So would an air gap work? I'm thinking basically a 3 sided retaining wall, then a 3" or so space topped with brick/stone for the upper side of the gap. We don't have much water running down the hill even in the heaviest rainfall that I've noticed in the 3 years I've lived here.

Yes, the good ol' "wet" retaining wall method works well. The trick is to drain that cavity with water outlets at each end. I've used the "wet wall" method for quite large construction projects.

[SableSprings]

As Mark noted, as long as the air gap chamber is drained and vented so the insulation layer never gets a significant amount of moisture "hanging around" the air gap will work. I'd also want to have some inspection port just to occasionally check that the chamber is remaining dry and has not been inhabited by critters. Also remember that a brick/stone top can easily develop cracks in the mortar or have other "seams" through which water may enter. The brick material will absorb water and pass it through to the air chamber, so in my mind having a heavy black plastic/visqueen layer over the top chamber bricks to inhibit moisture coming through from the top dirt layer would be a good investment.

[Gulf]

From the pic and the slope that you describe, I just don't see why the dome needs to be buried. The oven stand (partially). is a may be?. A one or two stage retaining wall could be place further back on the slope. I think that you may be creating future problems for yourself. Just my opinion.

[mongota]

From the pic and the slope that you describe, I just don't see why the dome needs to be buried. The oven stand (partially). is a may be?. A one or two stage retaining wall could be place further back on the slope. I think that you may be creating future problems for yourself. Just my opinion.

Agree. Berm the base, protect it with a foundation-type waterproof coating on the below-grade portion of the exterior.
The build a "typical" brick fire dome on top of the earth-bermed base.