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31"/800mm in Eindhoven, the Netherlands: Design critique and build topic

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  • 31"/800mm in Eindhoven, the Netherlands: Design critique and build topic

    As discussed in my introduction topic I"m building a WFO on top of a 'technical space' for rainwater irrigation. The core idea is to combine a barbecue area in the gallery with a normal domed pompei style oven, kind of like Sixto has done, but probaby with a smaller gallery. Bricks will be cut using the google sheet shared here by Deeyayoh and an IT will be used. After going through the forums for some time and trying out some different brick designs in CAD I've got an 80% matured design in mind. Please find the drawings attached (using sensible units mostly, but 'freedom' units for some of the main dimensions such that the design intuitions of you guys living on the other side of the pond are also triggered ).

    Construction wise I've poured the floating slab on which the oven will sit and I'm basically at the phase of finalizing the design and shopping around for materials. I'm not sure yet if I'll start oven construction this year as (wet) winter is already coming and it might make more sense to first finalize the tech space underneath the oven. What I'm looking for by posting this is:
    - Critique/questioning of my design: did I miss things? Would you do things differently?
    - Sharing my design/build experience such that others can also learn (like I have from on all the great posts here)
    - Documenting the build

    Base design:
    My base consists of a single brick U-shape that supports a first 3"/80mm reinforced slab. On top of that is an open space of 120mm/5" to be used for tool/bbq part/wfo door storage. On top of that is the actual 5" slab that holds the WFO. The slab that will hold the WFO juts out from this significantly (see drawing). The main rebar in the floating slab is 8mmx150mm square (.3"x6") with a significant amount of local extra support welded in (see picture). According to my calculations this should all hold up fine (safety factors of 3-5x), but critique is welcome from any structural people about this as well on if the single brick U-shape should be improved. The center of gravity of the slab and the oven will still be well inside the U and therefore the foundational slab will also be loaded properly. Compressional strength of the bricks and the mortar is fine, and also buckling loads are more than 10x away from expected loads.

    Hearth dimensions:
    hearth (inner) diameter 31"/800mm
    dome inner height 16.6" / 422 mm
    Entry arch height 10.5" / 267 mm
    Entry arch width 15.7" / 400 mm
    Oven floor height wrt ground level: 41" / 104cm

    The philosophy for these dimensions are mainly that I'm quite limited in the total size of the wfo due to the side of our garden and the location of the slab. The vent arch dimensions are such that our biggest pots would fit in for a roast/stew/bread baking etc. Height is based mainly on the fact that the higher you get the more convenient it becomes to look into the oven (+ the tech space underneath also needs room).

    Gallery and insulation dimensions:
    slab: 5" /125mm with 4 weep holes underneath the hearth
    glued broken tile for water channels
    Calsil 2" / 50mm
    1.6" 40mm dense fire stone tiles for the floor

    half-size firebrick (4"x4"x2" / 105x105x55mm) cut to size + homebrew mortar
    2"/50mm insulation blanket
    2"/50mm verticrete/render finish
    Probably with a vent port on top (still to be detailed)

    22" / 560mm wide (matching a grill size that will fit in setback mortar joints)
    12" / 306mm deep ("")
    13.8" / 350mm high (this might have to be increased by one brick for slighly better viewing angles, see section B-B in the drawings)
    See the drawings for the changeover to the chimney: I'm not sure yet about this area. I'm mainly worried about the thrust since now all chimney mass is going to directly push onto the arch, instead of being supported on the sides of the gallery. I might add buttresses or widen the chimney (which would increase the weight, and would not work brick-size wise). In the end at least everything should go into a 6"/150mm inner diameter double walled chimney pipe. There's currently a WAF (Wife acceptance factor) here as she doesn't like the chimney not being 'in the middle' of the dome. I don't want to do it with bricks as it will significantly increase the weight of the chimney (and be very challenging to make), and doing it with 45 degree bends in the pipe to me seems just as ugly. I'll browse the forums more if I see any good examples here, but suggestions are welcome.
    The idea would be to have an L-shaped thermal heatbreak filled with insulating rope and high temperature kit between entry arch and gallery, not sure yet if it also makes sense to make this in the floor (like with a piece of steel like Gecko has done). But I think it makes sense to have the heat break overall: the pizza oven will be much hotter than the gallery, and when using the bbq the oven will be much colder than the gallery.
    For the BBQ inside of the gallery the plan would be to weld/order a sheet metal 'drawer/ash box' and just let that rest on the gallery floor, suspending two grilles/grates above that in setback mortar joints: the lower one to support coals, the top one to actually grill the meat.

    Still to do in this area:
    • Possible plans for a rotisserie still to be detailed, main parts should be located in the door,with maybe just an insulated bush in the inner dome wall opposite the entry arch.
    • (double) Door design --> probably a detachable handle such that the BBQ can be used without interfering with a handle. Possibly also an outside door to entrap heat in the BBQ area.
    • Possibility to add a thermocouple through one of the weep holes into the floor tiles --> IR gun is probably going to be better/easier
    • Tie-in the gallery to the dome? I'm slightly worried about the structural integrity and I"ve seen 'thermal tie-in's which allow movement (ie. with an U-shape in the middle). If these are made out of steel I'd say the heat leakage would not be significant if I add in 2 on each side of the entry arch while they would add significant mechanical anchoring?
    • Chimney design as proposed: will the arch be able to support it? Butress the sides with a few more bricks to the sides?
    • I've seen some people incorporate valves in their chimney. Is this useful/needed?
    • Trade-offs on the height of the gallery: vision vs bending vs good draw
    • Chimney pipe routing to middle of the dome?
    • Base/foundation construction: do you see issues here?
    And of course please find attached pictures of the work and the current status.

    Attached Files
    Last edited by Toiletman; 09-06-2023, 10:42 AM.
    Only dead fish go with the flow

  • #2
    And the current status:
    Only dead fish go with the flow


    • #3
      Update: formwork fully removed. Pretty happy with the result. One of the weep holes got moved though, so I have to see if I'll be able to drill it through and make it function properly, instead of as a 'concrete splitter by freezing'. I'll post a separate reply with some design pictures/questions later.
      Only dead fish go with the flow


      • #4
        And here's some 3D views for the people that didn't view the pdf drawings, or find it hard to go from 2D to 3D:
        As mentioned before, main area's where'd I'd like to get some advice:
        - heat break between gallery and main dome: does this kind of design make sense? Should I put some 'expandable' tie-ins in?
        - Should meaures be taken to lead away the thrust of the gallery arch more? Ie. add butresses somehow? (I kind of like the current elegance of a brick and a half in depth, and wouldn't know how to elegantly add a brick perpendicular to this?)
        - Depth/height of gallery ok?
        - To accommodate the grill in the gallery I'd like to user larger joints in the gallery than in the dome: would you see any risks in doing this or would the homebrew mix be able to deal with this without problem?
        Only dead fish go with the flow