Variant 05-A
Two-layer clay oven
Wood-fired clay-and-sand dome wrapped in clay-and-straw insulation: door height, layer thicknesses and clay, sand and straw amounts for your size.
Not yet Reviewed
- Insulation layer: clay + straw, 4 in
- Heat-storing layer: clay + sand, 3.5 in
- Sand form, dug out after the first layer: 27 in across, 16 in high
- Door: 12 in wide, 10.1 in high, open through both layers
- Firebrick floor, 2.5 in
- Insulation under the floor, 4 in
- Base: non-combustible masonry, with a 16 in landing in front of the door
Cut in half through the door, to scale (the base’s height is up to you).
Parts at a glance
| Part | Amount | Rating |
|---|---|---|
| 16 | laid flat | |
| 6 buckets | reusable | |
| 7 buckets | both layers | |
| 5 buckets | 1 clay : 2 sand | |
| 19 buckets | 1 clay : 4 straw |
8 checks passed
- Inner diameter is 27 in, within the plan's 24–27 in.
- Dome height is 16 in, within the plan's 15–18 in.
- The dome is lower (16 in) than it is wide (27 in), as the plan intends.
- Door height is 63% of the dome height, within the plan's 60–66%.
- Door width is 12 in, no wider than half the floor (13.5 in).
- Heat-storing layer is 3.5 in, within the plan's 3–4 in.
- Insulation layer is 4 in, within the plan's 3–5 in.
- Your base must carry about 520 kg while you build (wet layers and the sand form) and 450 kg once dry, plus its own weight. Build it of non-combustible masonry (stone, brick or concrete), with no wood under or inside it.
Variables
in
in
in
%
Result
- Door height
- 10.1 in
- Door width
- 12.0 in
- Widest door allowed
- 13.5 in
- Width outside
- 42.0 in
- Height outside
- 23.5 in
- Space inside
- 100 L
Variables
Heat-storing layer: clay and sand
in
Insulation layer: clay and straw
in
Buying
%
L
Result
- 93 L
- · damp clay, loose
- 39 L
- · sand, loose
- 78 L
- 162 L
- · damp clay, loose
- 85 L
- · straw, loose
- 342 L
- 58.0 in × 66.0 in
- 16.0 in
- Rim beside and behind the dome
- 8.0 in
- Hearth top thickness, at least
- 4.0 in
- Insulation under the floor
- 4.0 in over 42.0 in square
- 16
- Weight while building (wet, with sand form)
- 520 kg
- Weight finished and dry
- 450 kg
- 4.6 m (15 ft)
- Ashes in a lidded metal bucket, away from anything that burns
- 0.6 m
Safety: required never skip · Recommended good practice, not a safety need · Only if needed the name says when
| Part | Qty | Your unit price (₱) | Subtotal (₱) |
|---|---|---|---|
| Base & floor | |||
| Your base: non-combustible masonry (stone, brick or concrete block) with a level top at least 4 in thick, 58 in wide × 66 in deep, able to carry 520 kg. No wood under or inside it.Safety: required | 1 lot | — | |
| Insulation under the floor, 4 in thick over 42 in square: glass bottles set in sawdust-clay, or perlite or vermiculite mixed with clay slip (127 L, with 10% extra for spills)Needed | 7 bucket | — | |
| Fine sand to bed and level the floor bricks, about 0.5 in (5.2 L, with 10% extra for spills)Needed | 1 bucket | — | |
| Firebricks for the oven floor, 9 × 4.5 × 2.5 in, laid flat over the 27 in floor (10% extra for cuts)Needed | 16 | — | |
| Sand form | |||
| Damp sand for the form, reusable (100 L)Needed | 6 bucket | — | |
| Heat-storing layer | |||
| Clay subsoil, damp and crumbled, for both layers (43 L heat-storing + 94 L insulation, with 10% extra for spills)Needed | 7 bucket | — | |
| Sand for the 1 clay : 2 sand mix (86 L loose, with 10% extra for spills)Needed | 5 bucket | — | |
| Insulation layer | |||
| Straw, loose, for the 1 clay : 4 straw mix (376 L loose, with 10% extra for spills)Needed | 19 bucket | — | |
| Door, rain cover & fire safety | |||
| Baking door to close the 12 in wide × 10.1 in high opening: thick hardwood board soaked in water before use, or sheet metal, with a handle. Take it out while the fire burns.Needed | 1 | — | |
| Rain cover: a roof of metal sheet on metal or masonry posts, open at the sides so smoke escapes, over the 58 in wide × 66 in deep hearth, or a lime plaster coat and a cover taken off and kept 4.6 m away before every fireNeeded | 1 lot | — | |
| Metal bucket with a tight lid, for ashes and embersSafety: required | 1 | — | |
| Water within reach while firing: garden hose, full water barrel or a fire extinguisher rated 4-A or moreSafety: required | 1 lot | — | |
| Total (12 parts not priced) | ₱ 0 | ||
Enter your supplier's prices to get a total.
- Choose the spot. Keep the oven at least 4.6 m (15 ft) from buildings, fences, wooden posts, overhanging roofs, tree branches, firewood and anything else that burns, above as well as around it. Ask your local fire office: some treat a wood fire outdoors as outdoor burning, which in the Philippines needs 15 m from any structure.
- Build the base. Build a level base of non-combustible masonry (stone, brick or concrete block, no wood under or inside it), with a top at least 4 in (10 cm) thick and 58 in (147 cm) wide by 66 in (168 cm) deep: the 42 in (107 cm) dome, a 8 in (20 cm) rim at the sides and back, and a 16 in (41 cm) landing in front of the door. It must carry about 520 kg while you build (wet clay and the sand form) and 450 kg once the oven is dry, plus its own weight.
- Insulate under the floor. At the back of the hearth, leaving the landing in front clear, lay 4 in (10 cm) of insulation over a 42 in (107 cm) square: glass bottles set in sawdust-clay, or perlite or vermiculite mixed with clay slip. Without it the base soaks up the heat the floor needs.
- Lay the floor. Spread about 0.5 in (1 cm) of fine sand on the insulation, mark a 27 in (69 cm) circle (the inner floor) with the door side facing the landing, and lay 16 firebricks flat and level to cover it, cutting the edge bricks to the circle.
- Build the sand form. Pile damp sand on the floor circle and shape a dome 16 in (41 cm) high. Cover it with wet newspaper so the clay doesn't stick to it.
- Test batch. Measure clay as damp, crumbled clay subsoil (not dry powder, not runny slip). Mix a small batch of each mix, press a fist-sized ball and let it dry. If it cracks, add sand (or straw) next time; if it crumbles, add clay. Enter the parts that worked in "Layers & mixes": the amounts update.
- Heat-storing layer. Mix 1 part clay to 2 parts sand, just wet enough to hold a shape, and pack it over the form 3.5 in (9 cm) thick, pressing it firm. Keep the thickness even all over.
- Cut the door. Once the layer is firm, cut a door 12 in (30 cm) wide and 10.1 in (26 cm) high (63% of the dome height) facing the landing, then dig the sand form out through it.
- Insulation layer. Stir clay into water to a thick slip, toss it with loose straw (1 part clay to 4 parts straw) until every straw is coated, and press it on 4 in (10 cm) thick over the heat-storing layer. Keep the door opening clear through this layer too: same width and height, edges finished smooth.
- Keep the rain off. Clay melts in rain. Put a roof of metal sheet on metal or masonry posts over the oven, open at the sides so smoke escapes, or finish it with lime plaster and use a cover that you take off and keep well away before every fire.
- Dry slowly. Let the oven dry out of strong sun and rain for at least 7 days, until there are no dark damp patches and the outside no longer feels cool. Don't light a full fire while the clay is wet: trapped water turns to steam and can crack or burst the layers.
- First fires. Light 7 small fires, one a day: the first only paper and kindling (about 93 °C, 200 °F), each a little bigger, about 56 °C (100 °F) hotter, up to about 427 °C (800 °F). Let the oven cool fully between fires. Steam and fine cracks are normal; deep cracks mean slow down.
- Fire safely. Never leave a fire alone, and keep a garden hose, full water barrel or fire extinguisher (rated 4-A or more) within reach. Take the door out while the fire burns: a wooden door can catch fire, so put it back only after you rake the fire out to bake. Put ashes and embers in a metal bucket with a tight lid on bare ground or stone, at least 0.6 m (2 ft) from anything that burns, or 3 m (10 ft) if it has no lid.
No Philippine standard covers earth ovens, so this plan uses the earth-oven method of Kiko Denzer’s "Build Your Own Earth Oven", international fire and fireplace codes, and published material figures. Values marked "not yet checked" come from secondary sources; values marked "assumption" are this plan’s own estimates. Test a small batch and check with your local fire office.
Shape
- Door height63% of dome height
- At about 63%, smoke and cool air leave over the door while the hottest air stays in the dome. Higher loses heat; lower smokes and draws badly.
- Source Kiko Denzer, "Build Your Own Earth Oven" (not yet checked against the book).
- Door width12 in, at most 50% of the floor (13.5 in)
- A door no wider than half the floor keeps the heat in and leaves enough dome to stand over it. Make it wide enough for your peel and pans.
- Source Kiko Denzer, "How wide a door?", handprintpress.com/tech/how-wide-a-door (the author’s website, not the book; not yet checked).
- Dome shape16 in high, 27 in across
- A dome lower than it is wide keeps the hot ceiling close to the floor: faster heating, even baking.
- Source This plan’s design.
- Plan rangesfloor 24–27 in, height 15–18 in, door 60–66%, heat-storing layer 3–4 in, insulation 3–5 in
- The sizes this plan is designed for. Outside them the checks warn and say which way to go.
- Source This plan’s design. Door ratio: Kiko Denzer, "Build Your Own Earth Oven" (not yet checked against the book).
Layers
- Heat-storing layer3.5 in of 1 clay : 2 sand
- Dense clay and sand store the fire’s heat and give it back during baking. Sand stops the clay shrinking and cracking as it dries.
- Source Kiko Denzer, "Build Your Own Earth Oven" (not yet checked against the book).
- Insulation layer4 in of 1 clay : 4 straw
- Air trapped in the straw keeps heat in the heat-storing layer instead of losing it outside, and keeps the outside cool enough not to burn.
- Source Kiko Denzer, "Build Your Own Earth Oven" (not yet checked against the book).
- Clay is measured damp
- Mix parts count damp, crumbled clay subsoil, not dry powder or runny slip. Clays differ: the test batch tells you whether to add sand or clay, and the amounts follow the parts you enter.
- Source This plan’s design.
Base and hearth
- Non-combustible basetop at least 4 in thick
- Hearths are masonry or concrete on non-combustible supports, strong enough for their own weight and the load, with no wood left under them.
- Source International Residential Code R1001.9–R1001.10 (masonry fireplace hearths), written for indoor fireplaces: the nearest code rule. R1001.9.
- Landing in front of the door16 in
- Embers and hot tools come out of the door: they need masonry to land on, and you need a shelf to set things down.
- Source International Residential Code R1001.9–R1001.10 (masonry fireplace hearths), written for indoor fireplaces: the nearest code rule. R1001.10 (16 in in front of openings under 6 ft²).
- Rim beside and behind the dome8 in
- Assumption: borrows the code’s 8 in beside a fireplace opening, so the dome’s edge, drips and stray embers stay on masonry.
- Source Assumption: this plan’s estimate. Based on International Residential Code R1001.9–R1001.10 (masonry fireplace hearths), written for indoor fireplaces: the nearest code rule. R1001.10.
- Insulation under the floor4 in
- Without it the base soaks up the floor’s heat and the bottom of the bread stays pale.
- Source Secondary sources, not yet checked: Denzer’s ovens use about 4 in of bottles in sawdust-clay (handprintpress.com, thefreshloaf.com); Forno Bravo’s oven plans use 4 in of vermiculite concrete.
- Firebrick floor9 × 4.5 × 2.5 in, about 3.6 kg each, +10% for cuts
- A hard, flat floor that stands the fire and the peel. Extra bricks are an assumption for cutting the round edge and breakage.
- Source Standard 9 in firebrick, about 8 lb (manufacturer and retailer listings; not yet checked: weigh yours). Extra: assumption.
Fire safety
- Distance from anything that burns4.6 m (15 ft)
- Sparks and heat leave the door and the dome. Keep buildings, fences, roofs, branches and firewood this far away, above too. The Philippine fire code asks 15 m for outdoor burning: ask your local fire office which applies.
- Source International Fire Code 307.4.3 (portable outdoor fireplaces) and 307.5 (attendance and extinguishers). Fire Code of the Philippines, RA 9514 IRR 10.5.4.4 (outdoor burning). Not yet checked with the Bureau of Fire Protection.
- Water at hand, never alone
- A fire must be watched until it is out, with a hose, water barrel or extinguisher (4-A or more) ready.
- Source International Fire Code 307.4.3 (portable outdoor fireplaces) and 307.5 (attendance and extinguishers). Fire Code of the Philippines, RA 9514 IRR 10.5.4.4 (outdoor burning).
- Ashes and embers0.6 m in a lidded metal bucket, 3 m otherwise
- Ashes stay hot for days. Keep them in metal, lid on, on bare ground or stone.
- Source International Fire Code 305.2 (hot ashes and embers).
- Door out while firing
- A wooden door next to the fire can catch fire. Put it in only to bake, after raking the fire out.
- Source This plan’s design.
Drying and first fires
- Slow dryingat least 7 days
- Clay shrinks as it dries. Slow, even drying stops the surface shrinking faster than the inside and cracking. Water trapped inside turns to steam in a big fire and can burst the layers.
- Source Kiko Denzer, "Build Your Own Earth Oven" (not yet checked against the book). Wait time: Forno Bravo oven-curing guide (community.fornobravo.com), a pizza-oven maker’s schedule applied to an earth oven: not yet checked for earth ovens.
- First fires7 fires, 200–800 °F
- Small fires that grow a little each day drive the last water out gently. Letting the oven cool between fires keeps the stress low.
- Source Forno Bravo oven-curing guide (community.fornobravo.com), a pizza-oven maker’s schedule applied to an earth oven: not yet checked for earth ovens.
Quantities and weight
- Dome volume
- Each layer is the difference between two half-ellipsoid domes, one inside the other. Real domes are hand-shaped: the amounts are estimates.
- Source Geometry: volume of a half-ellipsoid = ⅔ π r² h.
- Packing: clay and sand1 L loose makes about 0.8 L of layer
- Assumption: mixed and pressed, sand and clay fill each other’s gaps, as in mortar, where loose parts are about 1.27 times the finished volume.
- Source Assumption: this plan’s estimate. Based on the mortar dry-volume factor 1.27–1.33 (common building practice). Not yet checked.
- Packing: straw1 L loose makes about 0.35 L
- Loose straw squashes a lot: about 36 kg/m³ loose, while light straw-clay holds about 107 kg/m³ of straw.
- Source Loose chopped wheat straw 36 kg/m³ (Oak Ridge National Laboratory, osti.gov/biblio/984788); straw in light straw-clay 6.7 lb/ft³ (IRC Appendix BI, table BI103.2.3). Not yet checked for oven insulation.
- Packing: clay in the insulation1 L damp clay makes about 0.5 L
- Assumption: the clay becomes slip that coats the straw and fills part of its gaps, so it adds less volume than it takes up in the bucket.
- Source Assumption: this plan’s estimate. Not yet checked.
- Extra for spills10%
- Assumption: some material is always spilled or left in the bucket. Packing down is counted separately, above.
- Source Assumption: this plan’s estimate.
- Weightsclay-sand 1,900 kg/m³ wet, 1,800 kg/m³ dry; clay-straw 1,000 kg/m³ wet, 800 kg/m³ dry; damp sand 1,905 kg/m³; under-floor insulation 800 kg/m³
- Used for the load on the base. Wet weights are while you build; earth materials vary, so the figures lean heavy.
- Source Wet sand 1,905 kg/m³ (Engineering ToolBox); cob without fibre about 1,900 kg/m³ (Materials, MDPI 2024); light straw-clay 160–800 kg/m³ (IRC Appendix BI). Dry clay-sand, wet clay-straw and the under-floor layer: assumptions. Not yet checked.
- Clay slip
- Clay stirred into water until it is like thick paint. Coats the straw in the insulation layer.
- Door height ratio
- Door height as a share of dome height. At about 63%, smoke escapes over the door while heat stays in the dome.
- Earth (clay) oven
- Wood-fired dome oven of clay, sand and straw. Burn a fire inside, rake it out, then bake in the stored heat.
- Firebrick
- Dense brick made to stand fire without cracking. Used for the oven floor. Sold in hardware and kiln shops.
- First fires (curing)
- A few small fires, a little bigger each day, that drive the last water out of a new oven before full use.
- Hearth (base)
- Raised, level platform of stone, brick or concrete under the oven, with insulation and the firebrick floor on top and a landing in front of the door.
- Heat-storing layer (thermal layer)
- Dense inner shell of clay and sand. Soaks up the fire’s heat and gives it back slowly during baking.
- Insulation layer
- Light outer shell of clay and straw. Air trapped in the straw keeps the heat in.
- Landing
- The part of the hearth in front of the door, where embers, tools and hot pans land. Masonry, never wood.
- Non-combustible
- Can’t catch fire: stone, brick, concrete, metal, clay. Wood, bamboo and plastic are combustible.
- Parts (mix ratio)
- Amounts by volume, measured with the same container. "1 : 2 clay : sand" = one bucket of clay to two of sand.
- Sand form
- Temporary dome of damp sand shaped like the oven’s inside. Build over it, then dig it out through the door.
- Slow drying
- Drying wet clay gently over days or weeks, out of strong sun and rain, so it doesn’t crack.
These numbers are estimates. Check them against your own measurements and product labels before you build. Clay, sand and straw vary: test a small batch of each mix first. Never build where sparks or heat can reach anything that burns, never leave a fire alone, and check your local fire rules.