Permanent shelter

Do not import a technique that fights your materials. Dig below the dark topsoil — topsoil never goes in a wall, it contains organic matter that rots — and test the subsoil.

• Jar test: a third of a jar of subsoil, fill with water, add a pinch of salt, shake hard, let it settle overnight. Gravel and sand drop in seconds, silt in minutes to hours, clay over a day. Measure the layers.
• Ribbon test: squeeze moist soil between thumb and finger into a ribbon. Under 2.5 cm before it breaks is lean, over 5 cm is rich.

Cob and adobe want roughly 15–30% clay with the rest sand and gravel. Rammed earth wants less — around 10–20% — and more sand and gravel. Too much clay cracks as it dries; too little crumbles.

Earth buildings fail from water at the base, essentially never from load.

Foundation: a trench down to firm subsoil and below the frost line — typically 45–60 cm in a temperate climate — filled with rammed rubble or stone, and drained so water does not stand in it. Plinth: a stone or fired-brick wall on top of that, rising at least 30–45 cm above finished ground, above the height rain splashes back off the ground. Lay it in lime mortar, not cement, and slope the ground away from the wall.

Cob: tread subsoil, water and long straw together until the mix holds its shape and a handful pulled from it drags straw with it. Build in lifts of about 45 cm, pressing each into the one below, and let each firm for a few days before the next. Walls 45–60 cm thick for a single storey, tapering slightly as they rise.

Adobe: mould bricks around 25 × 36 × 10 cm from the same mix (in earthquake country, 40 × 40 × 10 cm blocks for a wall at least 0.40 m thick, as in the worked one-room earth house), dry them in the shade for a few days, then on edge in the sun for 2–4 weeks. A good brick dropped from 1 m onto a corner loses only the corner.

Rammed earth: slightly moist soil rammed in 10–15 cm layers in a formwork until the rammer rings rather than thuds.

Corners are where an earth building holds itself square, and an opening beside a corner is where cracks start.

• Keep doors and windows at least a wall's thickness plus a hand away from any corner.
• Keep the total width of openings on a wall to no more than about a third of its length.
• Lintels of seasoned timber or stone bear at least 30 cm into the wall on each side.
• Set door and window frames in as the walls rise, with pegs or wires built into the earth to anchor them.

Earth walls must not get wet from above. An overhang of at least 45–60 cm on every side, more on the weather side, and a roof steep enough to shed water fast:

• Thatch: pitch 45° or steeper, laid about 30 cm thick. Water reed lasts decades; straw lasts less. Steeper roofs last longer.
• Shingles and slate: around 30° and up.
• Clay tiles: around 35° and up, depending on the tile.

Tie the roof down to the wall plate — wind lifts roofs before it knocks walls over.

Earth walls must be able to dry out. Cement render traps moisture against the earth, which then softens behind a hard shell and fails invisibly until a section falls away.

Use lime plaster — see lime: about 1 part lime putty to 3 parts sharp sand, with chopped hair or fibre in the first coat. Apply in two or three thin coats, each allowed to firm before the next, onto a wall dampened first. Keep new lime out of direct sun and frost for a week or two, misting it so it cures rather than dries. Renew limewash every few years.

Thatch is excellent and free, and it burns.

• A chimney through thatch rises well above the ridge, is lined with fired clay or stone, and is swept on a schedule.
• Space thatched buildings apart — a planning figure of 10 m — so one fire does not take the settlement.
• Forge, kiln, smokehouse and tannery go downwind and at least 20 m from any thatch or dwelling.
• Keep water or sand stored by every building with a hearth.

Smoke indoors causes chronic lung disease and kills infants with pneumonia; a proper chimney is a health measure before it is a comfort.

Protecting the harvest and the tools returns more than comfort does — a granary saves the fifth of the crop that rats and damp take, and a workshop lets every other building go faster.

Then orient the dwelling: long axis east–west, main windows toward the winter sun (south in the northern hemisphere, north in the southern), the back or the store rooms toward the prevailing wind, and the smoky processes downwind of where people sleep. See the building guide.