Let each material reveal its own character (the grain of wood, the stratification of stone, the plasticity of concrete) and design each part in the way its material wants to be used.
At Fallingwater the stone of the walls is laid in rough, projecting courses like the ledges of the stream, while the concrete of the terraces, which can span and cantilever, is smooth, rounded at its edges and painted a light ochre: two materials, each doing what it does best. The rule descends from Ruskin’s truth to materials, but Wright made it a principle of form rather than of morals.
A thin curved shell carries load by the membrane forces in its surface, not by bending; so shape it to its loads and supports, and it can span great distances with a thickness of a few centimetres.
span ÷ thickness of a good shell ≈ 400–1000 (an egg: ≈ 100)
A fabric or cable-net roof is stable only if it is prestressed into an anticlastic (saddle) shape, curved upward in one direction and downward in the other, so that wind from either side meets a surface already in tension.
The outward form of a building should arise from, and express, what the building does and how it is made, as the form of every living thing expresses its life.
Show each material as what it is (brick as brick, timber as timber) and let the plan, rather than a symmetrical front, decide where the rooms, windows and chimneys go.
Shape a building to its place so that it seems to grow out of the ground: take its lines from the landscape, its materials from the region, and its plan from the life it will hold.
Commit no architectural deceit: do not suggest a structure other than the real one, do not paint or carve one material to look like another, and do not pass off cast or machine-made ornament as handwork.
Cite this page Chris Paton, “The nature of materials”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/nature-of-materials. Text, drawings and models licensed under CC BY-NC 4.0.