Plan the house: sun, air, smoke and damp

Decide where the fire goes before anything else. Household smoke killed about 2.9 million people in 2021 (WHO). Its two worst products are fine particles and carbon monoxide (WHO Housing and health guidelines, chapter 8), and in setting its limits WHO assumes that a stove with a flue still releases about 25 % of its emissions into the room (range 1–50 %). A chimney reduces the smoke but does not remove it. Plan for distance as well.

• Warm climates: cook outdoors under a shade roof or in a separate cookhouse, as UNHCR plans for camps.
• Cold climates: a separate kitchen room with its own door, the hearth against a stone or earth-block wall, and a hood and flue that rise clear of the roof, to the heights in the building guide. The full masonry chimney is the fireplace build.
• Never a brazier or a banked fire in a closed sleeping room. Carbon monoxide gives no smell and no warning (fire guide).

Plan for the household five years on, not today's. WHO's first housing recommendation (strong) is to prevent and reduce crowding: the evidence linking crowding to tuberculosis and other respiratory infections is rated high certainty.

• Floor: at least 3.5 m² of covered living space per person in a warm climate, not counting the cooking area, and 4.5–5.5 m² in a cold one, where people spend the day indoors (UNHCR, updated January 2026). The earth house, 14.4 m², sleeps four in the warm or three in the cold.
• People per room: more than 3 per habitable room is overcrowding (UN-Habitat); the stricter American index counts more than 1 per room as crowded and more than 1.5 as severely crowded.
• Height: at least 2 m at the lowest point in a warm climate, higher for air; no more than 2 m in a cold one, so there is less air to heat (UNHCR).

The day-night swing decides it. Heavy walls even out the swing; light walls let the house cool as soon as the air does. UN-Habitat's bioclimatic design guidelines (2016):

• Hot and humid (coast, lowland tropics): a lightweight envelope, rooms one deep so air crosses each, large openings, and a raised floor to cut heat from the ground.
• Hot and dry (desert, high swing): heavy walls and roof with a time lag of over 8 hours, small openings, compact or courtyard layouts. Close the openings by day and open them at night. This works where the night falls below 20 °C.
• Savannah and highland: medium weight, which evens out the swing; in the highlands, let the sun in for winter warmth.
• Cold winters: heavy floors and walls in the path of the sun store its heat (US DOE); keep windows small on the walls that face away from it. WHO proposes 18 °C indoors as safe in the cold season, and finds no demonstrable risk between 18 and 24 °C.

The building guide gives wall thickness, eave and plinth for each climate.

Plant a vertical stick on level ground and mark the tip of its shadow through the middle of the day. The shortest shadow falls at solar noon and points to the pole on your side of the equator: true north in the northern hemisphere, true south in the southern (sun geometry: PVEducation).

Then lay the long axis east–west, with the main openings in the long wall facing the sun:

• Outside the tropics: openings within 30° of true south (north in the southern hemisphere), and nothing that shades them from 9 a.m. to 3 p.m. in winter: no tree, wall or shed in that arc (US DOE).
• Between the tropics (latitude under 23.45°), the noon sun stands on the north side for part of the year and the south side for the rest. Keep the long walls facing north and south, keep east and west walls short with few openings, and shade every opening (UN-Habitat).

Work out the noon sun height for both solstices, outside the tropics:

• Shortest day: 90° − latitude − 23.45°
• Longest day: 90° − latitude + 23.45°

The shadow of the eave edge falls overhang depth × tan(sun height) below the eave. Worked example at latitude 40° (north or south): the noon sun stands 26.55° high in winter and 73.45° in summer. An overhang of 0.60 m, the rain eave of the earth house, throws its edge shadow 0.30 m below the eave in winter and 2.02 m below it in summer. So a window with its head 0.30 m or more below the eave takes the full winter sun, and a sill up to 2.0 m below the eave is in shade at summer noon. Nearer the pole the winter sun is lower: at 50° the same 0.60 m eave throws a winter shadow only 0.18 m deep.

Rain sets the minimum depth, deeper in wet climates (building guide). Where rain demands a deeper eave, raise it above the window head, not the window into the shadow. East and west sun comes in low, under any eave: keep those openings small.

Air crosses a room only between openings on opposite walls. The ventilation standard ASHRAE 62.1 (Addendum l, 2019), written for buildings other than homes, counts a room as naturally ventilated when:

• Its openable area is at least 4 % of the floor: 0.58 m² for a 14.4 m² room.
• Openings on opposite walls are no more than 5× the ceiling height apart: 12.5 m under a 2.5 m ceiling.
• With openings on one wall only, the room reaches no deeper than 2× the ceiling height: 5 m.

Put the inlet at body height on the windward wall and the outlet opposite, with a high opening to let out warm air and smoke (UN-Habitat). Moving air brings comfort up to about 32 °C outdoors when the air is humid; above 26 °C in dry air, open at night and close by day instead. In earth walls, large openings must still keep to the earthquake opening rules of the earth house. Build very open walls as light frames.

Damp is a planning decision: about 15 % of new childhood asthma in Europe is attributed to indoor damp (WHO Housing and health guidelines). Fix three heights on the plan before any digging:

• Floor above the design flood, with the margin fixed in the site record (choose the ground).
• Floor above the outside ground and plinth above the splash, with a damp-proof course on the plinth and the ground falling away. The heights are in the building guide's drainage chain.
• In hot, humid country, a floor raised clear of the ground on posts or a plinth keeps the floor cooler as well as drier (UN-Habitat).

Animals in their own building, not a lean-to on the house. The bugs that carry Chagas disease, which infects about 8 million people, mostly in Latin America, live in wall and roof cracks of homes and of chicken coops and pens around them (WHO, 2026). Plaster inside walls smooth with no cracks, and plan the shed, coop and dung heap downwind (animals).

Latrine: no more than 50 m from the house, so it is used at night (UNHCR), and at least 30 m from any groundwater source (UNHCR), downhill of it (latrine).

Injuries at home and in leisure kill about 110,000 people a year in Europe alone, and the WHO Housing and health guidelines recommend stair gates and window guards. Burns kill an estimated 180,000 a year, most in low- and middle-income countries; women and children are burned mostly in the kitchen, by open fires, unsafe stoves and spilled hot liquids (WHO).

• Enclose the fire and keep its flame low; a raised or walled hearth that a crawling child cannot reach or knock over.
• No hearth in a walkway or beside the door.
• Guard every edge above a fall: loft openings, raised floors, ladders and stairs, with a handrail.