Stone and earth building

Each stage has to be right before the next one covers it. A footing out of level makes a wall out of level, and a wall laid wet cracks under its roof. Treat the right-hand column as a gate: do not start the next stage until the check passes. The earth house gives the numbers for one real building.

Use what the site gives you. Three things decide the method, and each can be checked in a day: what the subsoil is (the tests below), whether there is stone, and whether there is straight timber. Then the climate and the local earthquake history narrow the choice.

• Clay-rich subsoil, little stone or timber: adobe or cob walls, on whatever stone you can find for the plinth.
• Sandy, gravelly subsoil with some clay: rammed earth.
• Plenty of stone: stone walls, dry-laid for field walls and in mud or lime mortar for houses.
• Plenty of straight timber: a timber frame with wattle-and-daub or plank infill, or a log building.
• Earthquake country: a light timber frame with light infill is safest. Build adobe there only with the ring beam and the reinforcement in the earthquake section.
• Most real buildings are hybrids: a stone footing and plinth, earth walls, and a timber ring beam and roof. That is the worked example.

Earth walls are heavy work. A 0.40 m adobe wall holds about 0.4 m³ (roughly 0.7 t) of earth per square metre, all of it dug, mixed and lifted by hand.

Hand tools only, and most can be made on site. The two tools that decide accuracy cost almost nothing. A water level is a clear tube filled with water: its two ends always show the same height, over any distance and round corners. A 3-4-5 cord is a 12 m loop knotted at 3 m and 7 m, which, pegged out tight, gives an exact right angle.

Choose the site.

• High ground that drains on every side. Stand on it after heavy rain: water must not lie anywhere within 3 m. Ask whoever has lived there longest where the water went in the worst year, and build above that.
• Firm, undisturbed ground. Not fill, not an old pit, not a slope that has slipped, not the foot of a scree.
• Clear of big trees by at least their height. Roots undermine footings, and branches fall through roofs in storms.
• Fire separation: thatched buildings about 10 m apart, and any forge, kiln or smokehouse at least 20 m away and downwind.
• Orientation: long axis east–west, and main windows toward the winter sun (south in the northern hemisphere, north in the southern). Put the storerooms or the back wall toward the prevailing wind, and the door on the sheltered side.
• Water within carrying distance: a one-room earth house takes 6–8 m³ of water to build.

Set it out.

1. Mark the outside face of one long wall with two pegs and a string.
2. At one end, peg out a 3-4-5 triangle: 3 m along the string, 4 m out from it, and pull the 5 m diagonal tight. The 4 m side is then square to the first wall.
3. Measure the other two sides and peg the last corner.
4. Check the diagonals. The two diagonals of a rectangle are equal. If they differ, move the last corner by half the difference until they agree within 10 mm.
5. Set profile boards (a horizontal board on two pegs) about 1 m outside each corner, and transfer the lines to them with nails or notches: one for each wall face and one for each trench edge. Then pull out the corner pegs. The boards survive the digging and re-set the strings at every stage.
6. Fix a datum, one height marked as a notch on a stake that nobody will disturb, and take every level from it with the water level.

Subsoil — the layer below dark topsoil — is the material. Topsoil never goes in a wall: its organic matter rots and it never holds.

The jar test — what is in it. Fill a straight-sided jar one-third with soil, add water to near the top and a pinch of salt, shake hard for two minutes, and set it down. Gravel and sand settle in a minute, silt in an hour, clay over a day or more. Measure the layers.

The ribbon test — how much clay. Squeeze a moist ball of soil between thumb and finger into a ribbon. A ribbon over about 5 cm before breaking means a lot of clay.

For adobe, the EERI/IAEE adobe tutorial gives three field tests that settle the mix:

• Dry strength: roll five balls about 20 mm across, let them dry for 24 hours, and try to crush each one between thumb and forefinger. If none breaks, the soil has enough clay. If any crushes, it does not.
• Roll test: roll a thread of moist soil about 20 mm thick and let it hang from your fingers. If it breaks between 50 and 150 mm long, the soil is right. Shorter than 50 mm means too little clay; longer than 150 mm means you should add coarse sand.
• Sandwich test, for the mortar: join at least four pairs of blocks with mortars of soil and coarse sand (0.5–5 mm) in proportions from 1:0 to 1:3 by volume. Open them after 48 hours, and use the mix with the least sand that shows no cracks.

The drop test — right moisture for ramming. Squeeze a handful hard into a ball and drop it from about 1 m onto hard ground. It should shatter into a few pieces. If it flattens without breaking, it is too wet; if it will not hold together when squeezed, too dry.

Make test blocks before anything else. Mould five blocks of your chosen mix and dry them for three weeks. A good block dropped from 1 m onto a corner loses the corner and nothing more.

Earth buildings almost never fail from load. They fail from water: rain on the wall face, splash at the base, damp rising from the ground, and water running onto the site from uphill. Each has a fixed defence, and the defences only work as a chain. A good plinth under a roof with no overhang still erodes.

1. Roof: steep enough for its covering (table in the roof section), so water runs off before it soaks in.
2. Eaves: an overhang of at least 0.45–0.60 m, more in wet climates, so rain falls clear of the wall.
3. Drip strip: gravel under the drip line, about 0.8 m wide and 0.15 m deep, so drips do not splash mud onto the wall.
4. Plinth: stone at least 0.30–0.45 m above the ground, above the splash.
5. Damp-proof course on the plinth top (slate, tile or a salvaged sheet), so ground damp cannot wick into the earth.
6. Ground falling away by at least 5% over the first 3 m: 15 cm in 3 m, the figure the US residential building code uses.
7. Floor at least 0.15 m above the outside ground, on a gravel capillary break.
8. Cut-off drain on the uphill side: a gravel-filled trench to footing depth, falling at least 1% to an outlet downhill.

The test is the first heavy rain. Walk round the building and watch where the water goes.

1. Dig through topsoil to firm, undisturbed subsoil. Never build on fill, topsoil or freshly dug ground. Firm ground takes no print from your heel, and a steel bar will not push into it by hand.
2. In cold climates, go below the depth frost reaches. Water in the ground under a footing freezes, expands and heaves the wall, and each thaw it settles unevenly and cracks. A rubble trench (a trench below frost depth filled with clean, compacted stone and drained at the bottom) keeps water from collecting under the wall.
3. Make the footing about 1.5× as wide as the wall to spread the load: a 0.60 m footing under a 0.40 m wall. Lay the biggest flat stones first, long sides across the trench, with one stone reaching right across every metre.
4. Build a plinth of stone or fired brick to at least 30–45 cm above finished ground before any earth goes on it. This is the part that takes splash-back and wet ground. Level its top all round with a water level, to ±10 mm.
5. Lay a damp-proof course where the earth wall starts: two layers of slate or fired tile with staggered joints, or a bituminous or heavy plastic sheet. This stops moisture wicking up from the plinth.
6. Grade the ground away from the walls, and lead roof water away. Water pooling against a wall base is how most earth buildings fail.

A floor has one job beyond being flat: staying dry. Every design below starts the same way. Strip the topsoil inside the walls, ram the subsoil, and lay 0.15 m of clean gravel with no fines as a capillary break, so ground water cannot climb into the floor. The finished floor sits at least 0.15 m above the outside ground.

• Rammed earth: two or three 5 cm layers of damp, sandy clay subsoil, each rammed until the rammer rings. Let it dry and crack, fill the cracks with a thin clay slurry, then seal it: linseed oil in several coats where you have it, otherwise repeated clay-and-dung washes, renewed as they wear.
• Flagstones: flat stones bedded on 5 cm of sand over the gravel, with the joints filled with sand or lime mortar. Hard-wearing and washable.
• Lime (tier 2): lime and aggregate over the gravel, once you can make lime. See the lime guide.
• Raised timber in wet or flood-prone places: joists on stone pads over a ventilated air space. The granary shows the pattern.

A hearth goes on stone or fired brick, never on timber.

Rammed earth. Build strong formwork — boards bolted through on ties — the thickness of the wall. Fill in layers of 10–15 cm of loose damp soil, and pound each until the rammer rings rather than thuds; it compresses to about two-thirds. Move the forms up and along. The walls can be used almost at once and harden for months.

Cob. Mix subsoil, sand, water and straw on a tarpaulin by treading, turning, and treading again until it is stiff and sticky. Build in lifts of about 45–60 cm high, pressing and stitching each handful into the one below. Let each lift stiffen — days — before the next. Trim the faces with a sharp spade when leather-hard.

Adobe. Soak the soil for a day before mixing. The tutorial calls this "sleeping" the mud: it lets the water reach every clay particle. Tread in chopped straw, then press the mix into a wetted, bottomless wooden mould on a flat yard strewn with sand, and lift the mould straight off. Dry the blocks in shade for the first days, then on edge for 2–4 weeks. Test a block by dropping it from 1 m onto a corner: it should lose the corner and nothing more.

Laying adobe. Dip each block in water for about 5 seconds, so it does not suck the mortar dry. Use the mortar from the sandwich test, in joints of 10–20 mm, and fill the horizontal and vertical joints completely. Lay in running bond, with each block crossing the joint below it by half a block, and weave the corners by alternating which wall runs through. Build no more than about 1 m of height a day (published guidance runs from 1 to 1.5 m), or the fresh joints squeeze out and the wall leans.

Stone in mortar. Lay each stone on its broadest face with its length into the wall, and break the joints from course to course. Place a throughstone reaching across the wall about every metre, and build the corners from the largest, squarest stones, alternating their direction. Use mud mortar in dry climates and lime mortar where you have it, and point the outer joints hard.

Dry stone. No mortar, so the wall holds by gravity and friction alone.

• A wide base — roughly half to two-thirds of the height — tapering to the top, both faces leaning inward (the batter).
• Every stone set with its length into the wall, not along it.
• One over two, two over one — every stone crosses the joint below it. A vertical joint running up two or more courses is a crack waiting to open.
• Hearting — small stones packed firmly into the middle, not thrown in.
• Throughstones reaching right across the wall every metre or so, tying the two faces together.
• Cope stones on top to weigh down the final course.

Openings and corners are where earth and stone walls crack first. The rules below are the EERI/IAEE tutorial's rules for adobe in earthquake country. Outside earthquake country they still keep cracks from starting.

• No opening wider than 1.2 m.
• All the openings in a wall together take no more than a third of its length.
• At least 1.2 m of solid wall between an opening and a corner or cross-wall, and between two openings.
• Lintels bear at least 0.30 m into solid wall at each end. They run the full width of the wall and are made of seasoned timber or stone; green timber shrinks and cracks the wall above it.
• Frames go in as the wall rises, anchored with pegged timbers bedded in the joints. Never cut an opening afterwards.
• Corners are woven, not butted: alternate which wall's blocks or stones run through, course by course.
• Never enlarge an opening later without rebuilding the pier beside it.

Arches: spanning with stone. Stone and brick are strong in compression and weak in tension. They can be crushed only with enormous force, but they crack under bending, so a stone beam longer than a metre or two snaps under its own weight. An arch turns the load on it into compression all the way down to the ground, which is why stone could span rivers and roof cathedrals.

1. Build a timber centring, a curved wooden form the shape of the arch's underside, and support it firmly.
2. Lay the wedge-shaped stones (voussoirs) from both sides at once, each resting on the centring, working upward.
3. Set the keystone at the crown last. Until it is in, the arch is not an arch.
4. Leave the centring in place until the mortar has set, then lower it gradually and evenly.

An arch pushes outward at its base; this push is its thrust. The arch stands only if the walls or abutments at its feet are heavy enough to resist it, and flatter arches push harder. The line of the thrust must stay within the middle third of the arch and its supports, the classic masonry rule. A pointed arch thrusts less than a round one. Over a door, a small relieving arch built above a flat lintel takes the weight off the lintel.

A ring beam (also called a bond beam, collar beam or crown beam) is a continuous belt round the top of every wall. It makes four walls act as one box, spreads the roof's load along the walls, and gives the roof something to be fixed to. In earthquake country it is the single most important measure. Everywhere else it still stops corners opening as the building settles.

• Timber: two rails of about 75 × 75 mm, one along each face of the wall, joined by cross pieces every 0.40 m into a ladder the full width of the wall. This is the tutorial's specification. Eucalyptus poles or bamboo of 100–120 mm diameter do the same job.
• Continuous: it runs round every wall. At each corner the rails of the two walls cross, halved into each other and pegged, or nailed and wired once you have nails and wire. A ring broken at one corner is not a ring.
• Bedded on the top course in mud mortar, with mud and broken block filling the space between the rails.
• The roof is fixed to it: every tie beam or rafter foot is pegged or lashed to the ring, so wind cannot lift the roof off.

The earth house drawings show the ring at a corner.

Overhang first. Eaves should project at least 45–60 cm beyond an earth or lime-rendered wall, and more in wet climates. An overhang protects the wall better than any render, and costs only longer rafters.

The frame. The simplest roof that does not push the walls over is the rafter couple with a tie: two rafters meeting at the ridge, their feet joined by a tie beam at wall-top level to make a closed triangle. Rafters without ties spread under load and push the wall tops outward, and earth and stone cannot resist a push; the first sign is a crack at the top of every corner. Stand the couples on the ring beam at about 0.6 m centres, lay a ridge pole in the crotch, and brace diagonally until the battens are on. Then fix battens across the rafters at the spacing the covering needs. Take timber sizes from local practice or from calculation. The sizes in the worked example are illustrative, for a 4 m span under thatch.

Pitch depends on the covering: the less waterproof each piece is, the steeper the roof must be, so water runs off before it soaks in.

Weight matters in earthquake country. A light roof (thatch or shingles) is safer than heavy tile, and a flat earth roof on earth walls is what kills.

Household smoke from cooking and heating on open fires indoors kills an estimated 2.9 million people a year (WHO, 2021). A building that traps smoke is a health hazard, however well it is built.

• No open fire under thatch without a chimney. Until you can build one, cook outside or in a separate kitchen building.
• A chimney through or beside thatch rises 1.8 m above the thatch (UK guidance for thatched roofs). Line it with fired clay or stone and sweep it on a schedule, because soot and tar build up and catch fire.
• Through any other roof, a chimney must rise clearly above the ridge, or wind eddies push smoke back down it.
• Space thatched buildings about 10 m apart, and keep any forge, kiln or smokehouse 20 m away and downwind.
• Ventilate across the room: a window on one wall and a high vent on the opposite wall clear smoke and damp. Keep water or sand beside every hearth.
• Carbon monoxide has no smell. A fire burning in a closed room at night kills the people sleeping there. See the fire guide.

Adobe, rubble stone and unreinforced brick fail in earthquakes because they are heavy and brittle: the ground shakes sideways, the walls cannot bend, and heavy roofs and wall tops fall on the people inside. Where earthquakes have happened before, they will happen again, and these details decide who survives.

1. A continuous ring beam at the top of every wall, of timber or of reinforced concrete where available, tying all the walls together into one box. It is the single most important measure. See the ring beam section above.
2. Tie the roof to the ring beam, and keep the roof light. A heavy earth or stone roof is what kills.
3. One storey for earth. Walls at least 0.40 m thick, no taller than 6× their thickness (and never over 3.5 m), and no longer than 10× their thickness (never over 7 m) between corners or cross-walls. Otherwise add a cross-wall or a buttress.
4. Reinforce the walls. The adobe tutorial shake-tested several options. One is vertical cane inside the wall, with crushed cane laid flat every fourth course, all tied to the ring beam. Another is an outside mesh of vertical cane and horizontal rope about 0.45 m square, plastered over.
5. Keep openings small, few and away from corners, following the rules in the openings section.
6. Build symmetrically, on a simple square or rectangular plan. L-shapes and irregular plans twist and tear at the joints.
7. Timber-framed walls with light infill (wattle and daub, or small units in a frame) bend and survive where solid masonry collapses. Traditional building in many earthquake regions uses exactly this.

The same house is not right everywhere. The worked example suits a temperate climate with a dry season. Change it like this:

Find the cause before you repair the damage. Patching a crack or re-plastering a wet wall without fixing what caused it buys one season.

An earth building lasts as long as its roof, its plaster and its drainage are kept up. Each job is small if it is done on time.

• Before this: Shelter and body heat keeps people alive through the first weeks, and A cutting edge makes the timber work possible.
• This guide serves: Permanent shelter, the step that lets a group stop moving and start storing.
• What it unlocks: Livestock (housing for animals and fodder), Woodworking and the first machines (a dry workshop), Keep watch and defend the settlement, and later Plot, street and block.
• What improves on it: Brick and tile and Lime in tier 2, then Cement and concrete in tier 3. Each makes walls and roofs more durable against water, but none of them changes the rules above.
• Build it: the one-room earth house, after the raised granary, as the ladder advises.
• The next dwellings: the masonry house and chimney at tier 2, with the fireplace and chimney build, then the framed and glazed building at tier 3. See every level of the Dwellings track.