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Lower ground floor court yard

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  • Lower ground floor court yard

    Hi everyone,

    I want to build a pizza/bread oven in our garden.

    The problem: We don't have a big garden (we live in a town house in central Brussels) so I don't have anywhere to put it.

    The solution (or the only solution my wife has agreed to yet): At the back of the house, the ground is level with the ground floor, but there is a small courtyard to the lower ground floor or 'sous-sol' as it's called here, see photo. Towards the garden, the small courtyard ends with a wall 150 cm high and 30 cm wide. Behind it I have my bbq area, Weber, small kamado, dustbin tandoor, etc.

    My plan: Break through the wall for the opening of the pizza oven and dig a hole behind it, build the oven in the whole and fill it up, put back tiles and then I would have a oven that hasn't taken a single square cm of space in my garden.

    My questions: Has anyone done this? What advice do you have for me?

    What shape? Dome or barrel?

    Thermal mass? Brick thickness?


    Supportive concrete layer? Above and not below, or both?

    I'd be ever so grateful for any help on this!


  • #2
    Look at david s ovens, he has done a numberbof small diameter cast dome ovens. Small foot print but enough size to do pizzas and roasting.
    Google Photo Album []


    • #3
      You may have a problem if your oven is below the level of your garden. Ovens will pick up moisture easily because of the nature of porous refractory materials. Most oven owners find that moisture is their enemy and find it reduces the ovens efficiency. Your plan would also mean a very low working height. I think you may find a better plan would be to buy a small oven kit and mount it on top of that low wall with some extra support behind it.
      Kindled with zeal and fired with passion.


      • #4
        You can can use xypex in your hearth to waterproof the concrete if you want to do something on grade/sub grade. you need to basically build a water proof box - and as david points out you will still have an uncomfortable to work with oven.
        My build progress
        My WFO Journal on Facebook
        My dome spreadsheet calculator


        • #5
          Thanks for great answers!

          The image is maybe a bit misleading. The wall is 170 cm high so with a dome height of 50 cm for example would give an oven floor at almost normal kitchen top level.

          Waterproofing the bottom slab is a great idea. I also thought of putting a few inches of gravel under bottom slap for drainage (I used this very successfully to insulate the lower ground floor, dug out, 10 cm gravel, on top a floating construction of extruded styrofoam, fiber plaster boards (like Knauf Brio) and then tiles on top)

          I will of course also have to see when I dig out if it is dry. It's generally sand under the top soil and quite dry, but you never know.

          It's also a question of size, People here seem to build quite large, but I've seen that you are happy with your 21' David.

          Last edited by HenrikK; 02-06-2018, 12:30 AM.


          • #6
            I also thought of putting a few inches of gravel under bottom slap for drainage
            You may also want to include gravel on the sides.
            Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build


            • #7
              Yes, Gulf, that's a good point, any humidity would drain down the edge of the soil and not reach the WFO which would lower the pressure on any water-proofing

              On shape: The wall is 40 cm thick so the entrance before the chamber would be 40 cm or 16''. What shape should I choose for the chamber given that?


              • #8
                The hemisphere shape is the easiest to build. Also, with a deep entry, the barrel vault design wold make for an even farther reach imo.
                Think, and rethink any and all ways of keeping ground moisture from getting to the oven and it's insulation. I did a french drain around my oven stand which is built into a retaining wall. I'm glad that my oven is not also under grade.
                Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build


                • #9
                  A lovely sunny day here in Brussels. I started digging. At - 60 cm gravel mixed with what remains of older buildings (our house is from 1886). First 20 cm sand, then soil for another 20 and then the gravel mix. Its humid but not wet. I definitely need to waterproof the edges before building an oven in it.


                  • #10
                    The ground level must have been lower at some point. 12-15 cm below current ground level there is on each side what remains of a 10 cm thick concrete slab. This opens interesting possibilities for the construction as I would have absolute stability in the both sides of the oven that are 90 degrees to the opening.


                    • #11
                      An update. I'm trying to make a waterproof box to build the oven in. First step, gravel in the bottom and on top perlcrete with SIKA waterprofing agent . Talked to someone at SIKA who said it ought to work, but let's see. Plan to let it sit until the weekend to harden before trying to make the sides of the box. Do you think this would work?


                      • #12
                        What are your thoughts of placing perlcrete below grade?
                        Google Photo Album []


                        • #13
                          I really think you are asking for trouble. See previous comment.


                          i use an additive (Xypex) to make my supporting slab waterproof, but have found using the recommended additions that it is only partially effective. Remember that even if you made it totally waterproof to prevent moisture getting in, it will also act to prevent moisture getting out.
                          Dry insulation like cal sit board is preferable to vermicrete because it is already dry but costs considerably more. Look at my experiment on attachment re drying vermicrete

                          If you could maintain an airspace of around 100 mm surrounding the sides of the insulation it would be better, but it will fill up with all sorts of rubbish from your garden and you'll be back to square one. Moist insulation is not very effective as it will conduct heat.

                          Vermicrete insulating slab
                          Attached Files
                          Last edited by david s; 02-21-2018, 04:18 AM.
                          Kindled with zeal and fired with passion.


                          • #14

                            it's not an option to leave any open space around the oven. The agreement is that i must seal and put back the tiles afterwards so that the top looks like it did before I started.

                            deejayoh said above that i would have to build a waterproof concrete box and put the oven inside it. That's what I'm trying to do. As the ground provides structural support, I thought I might as well try to give the waterproof box insulating properties too.

                            One more reason for going the route of a waterproof box is that I dont want to drain the ground in this area of the garden too much


                            • #15
                              In that case don't use vermicrete or it may never dry in there, just use the cal sil board.
                              We just give advice based on our knowledge and experience here and that does not always mean we agree with each others opinions. I can't be sure that your plan won't work, but I am sceptical. I guess the only way to find out is to build it and report back, good luck.
                              Last edited by david s; 02-21-2018, 04:31 AM.
                              Kindled with zeal and fired with passion.