Make the roof flat and use it: a garden and terrace that gives back to the building the ground it covers, drained inward and kept watertight by a continuous membrane.
The roof garden is the fourth of Le Corbusier’s five points. Reinforced concrete made a flat roof structurally easy, and he argued that a planted roof protects the concrete from heat and cold while restoring the lost ground as an outdoor room. The flat roof became the emblem of the Modern Movement, and its weak point, since early membranes cracked and leaked. It was not new: in the dry climates of Egypt, Mesopotamia, the Maghreb and northern India flat earth roofs had always been terraces for sleeping and drying crops.
A saddle surface in which two opposite corners are raised and two lowered is a hyperbolic paraboloid; it contains two families of straight lines, so it can be formed with straight boards and yet has double curvature.
y = k·x·z (or any bilinear patch through four points not in one plane)
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)
Span the whole depth of the building with the structure so that each floor is a single open plate, adaptable to uses that cannot be foreseen.
Pompidou: 48 m clear span between column lines, 13 bays of 12.8 m
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.
Omit applied ornament from buildings and everyday objects: it wastes work, money and material, dates quickly, and adds nothing that fine material and exact workmanship cannot give.
With a concrete frame, a house should stand on pilotis, have a free plan and a free façade, be lit by horizontal ribbon windows, and carry a garden on its flat roof.
pilotis · free plan · free façade · ribbon window · roof garden
Cite this page Chris Paton, “The flat roof as a garden”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/flat-roof-garden. Text, drawings and models licensed under CC BY-NC 4.0.