Thatch, mud and stone: building with what is within reach

Before industrial transport, building material had to come from nearby, because moving heavy material was expensive. The result is that traditional buildings are made of whatever the local geology and vegetation supplied, and that building styles change wherever the geology does.

Earth

The most widely used building material in human history, and still housing a large share of the world's population.

Adobe — sun-dried mud bricks, generally with straw or fibre added to reduce cracking. Simple, effective in dry climates, and requiring maintenance where it rains.

Rammed earth — damp soil compacted in formwork in layers. Produces very solid walls and is labour intensive. Structures built this way have stood for centuries.

Cob — a stiff mix of earth, water and fibre built up in courses without formwork or bricks, shaped by hand. Characteristic of parts of Britain and elsewhere.

Wattle and daub — a woven framework of sticks covered with a mud mixture, used as infill in timber-framed buildings across a very wide area.

Earth walls have high thermal mass, which is the reason they work so well in climates with a large difference between day and night temperature. They absorb heat during the day and release it at night, keeping the interior stable.

They also manage humidity, absorbing and releasing moisture, which affects comfort in ways that sealed modern construction does not replicate.

The vulnerability is water. Earth building requires a good foundation to keep ground moisture out and a good roof overhang to keep rain off — the traditional formulation is a good hat and good boots.

Thatch

Roofing with plant material — reed, straw, grass, palm leaf, heather — depending on what grows.

Thatch works by shedding water down the surface of tightly packed stems rather than by being waterproof. That requires a steep pitch and a considerable depth of material, which is why thatched roofs are thick and steep.

Well-laid water reed roofs can last for decades; straw thatch less; the ridge needs replacing more often than the rest.

The insulation is excellent, and the material is renewable and local. The disadvantages are fire risk, the labour involved, and the need for a specialist to lay it properly.

Thatching has survived as a trade in several countries, sustained by heritage protection and by a market for the appearance. The reed itself has become an issue, with much of it now imported, which somewhat undercuts the local-material logic.

Stone

Where stone is available, it is used, and the type available determines the technique.

Stone that splits into flat slabs produces one kind of wall and roof; rounded field stone produces another; stone that can be cut and squared produces a third.

Dry stone construction, without mortar, relies entirely on the placing of each stone, and a well-built dry stone wall is more flexible and more durable than a mortared one — it accommodates ground movement rather than cracking.

Stone roofs of split slabs are heavy and require substantial timber beneath, which is why they occur where the stone splits well and the trees are large enough.

Timber

Where forests were available, timber framing, log construction and plank building dominate.

Log building, where horizontal logs are notched at the corners, requires straight softwood in quantity and is characteristic of northern forest regions.

Timber framing, with a jointed skeleton and infill, requires less timber and more skill, and is found where wood was valuable enough to economise on.

The forms follow the climate

Roof pitch tracks rainfall and snow load. Overhangs track sun angle and rain. Wall thickness tracks temperature range. Window size tracks the trade-off between light and heat loss. Orientation tracks prevailing wind and sun.

These relationships are consistent enough that a building's form is a reasonably good guide to its climate, and the variations over short distances — a different roof pitch on the other side of a ridge — usually correspond to a real difference in exposure.

Why any of this matters now

Industrial materials removed the constraint, and buildings everywhere converged. The same construction now appears in climates it does not suit, compensated for with mechanical heating and cooling.

There is renewed interest in vernacular technique for reasons that are partly environmental — earth and timber have far lower embodied energy than concrete and steel — and partly about performance in climates where the traditional solutions worked well.

The obstacles are regulatory and practical. Building codes are written around industrial materials and testing regimes, and earth and thatch fit awkwardly. Finding skilled builders is difficult. And traditional buildings require maintenance regimes that modern occupants are frequently not prepared for.

Where the revival has worked best, it has generally been where someone did the work of getting the technique tested and certified, which is unglamorous and turns out to be the actual bottleneck.