Individual homes of cheaper construction are better suited for new experiments than large constructions built for rental purposes. At this time, one could easily have believed that because of the high price of building sites in the cities and because of the housing-shortage crisis, private mansions, enclosed between houses that rise to any height, would gradually disappear. But the periphery, or the suburbs, of large cities, remains an option; cars brought inhabitants closer to the centre. The housing shortage, a consequence of the interruption of construction caused by the war, and the temporary uncertainty of the value of money determined the revival and even proliferation around major urban centres; apart from the private mansion, the word would often be considered pretentious, at least referring to the small, family house. Here, a few young architects, such as Robert Mallet-Stevens, André Lurçat, Jean-Charles Moreux, and Henri Pacon, applied, with an intransigence which often does not exclude taste, their principles of rational distribution and construction. Thanks to bay windows that span the length of a room, obscure angles are avoided. Although they banished all decoration, they were concerned about practical details which were carefully studied: interior blinds, sliding doors and windows, saving space by not having to install cumbersome shutters. Uncluttered rooms, for them, meant supreme elegance.

      To carry out these various projects, from large factories to small houses, the architect takes advantage of the industry’s achievements. Materials are provided to him cheaply due to more time efficient working methods. The invaluable invention of plywood, which – unlike natural wood – does not warp over large areas, offered new facilities for the execution of panelling and doors. Rolled steel, the newest innovation to come out of factories, was more lightweight and resistant than its predecessors; they are invaluable to the halls of department stores and openwork façades of commercial buildings. They are also used in houses for window joinery; metal allows more light to stream through than wood. However, iron has well-known defects. For example, it oxidises if it is not protected by a coating and it requires constant monitoring, which can be expensive to maintain. One would agree with Auguste Perret when he said: “If man were to suddenly disappear, the steel and iron buildings would not be long in following them.”

      Fortuitously invented in 1849 by Joseph Monnier, a gardener of Boulogne, improved by the research of Joseph-Louis Lambot, cement or reinforced concrete consists of a mixture of cement, sand, and stones coating a steel reinforcement. The stones then act as a part of the inert material, like grease-remover mixed with earth in large ceramic containers. The relationship between the ratio of steel expansion and cement allows the concrete to lengthen while following the deformations of metal without falling apart, so that, in essence, the reinforced concrete behaves like a single entity. Reinforced concrete is well-suited for finer work. Cement hardens quickly, but it is breakable, making it better to use for posts and beams rather than hollow blocks because the works can be altered after a few days. The speed of its creation is comparable in speed to the assembly of iron frames which were prepared in advance with expensive machinery. Concrete made with clinker is less resistant to the pickaxe than granular cement and, hence, invaluable to temporary buildings. Used for roofs, floors, and partitions due to its light weight, it protects against heat and cold and often decreases the excessive resonance which comes with reinforced concrete constructions. The strengthened stone is a mixture of many materials, which makes it suitable for façade renovation. Whatever its varieties, this resistant material allows the fast construction of a structure in which the use of other materials might make the project more difficult and ultimately destroy it. A work thus built is an artificial monolith. It has justly been compared to the concrete buildings of Rome and Byzantium, where tensile brick framework played a role analogous to iron and concrete.

      The consequences of this discovery, from the point of view of construction, can well be seen: extraordinarily long lintels, long-ranging, continuous arcs made from a single piece, and strong and slender posts. The obstruction of the fulcrums is kept to a minimum much more easily than in Gothic constructions. Whilst the intersecting ribs required buttresses and flying buttresses to balance it out, the monolithic framework in reinforced concrete holds without external stays. The walls which do not support any weight but are mere partition walls, can be removed on the whim of the architect. He can replace a solid wall with a double wall to lock in an insulating air pocket. Engineers were the first to understand the part reinforced concrete could play in architecture. Anatole de Baudot, who had already preached its virtues through his teachings, employed it at the end of the 19th century at the Lycée Lakanal and the Church of Saint-Jean-de-Montmartre. He was only in the wrong to abuse narrow curves, whereas his technique was particularly suitable for rectilinear forms. Immediately after him, Charles Génuys gave reinforced concrete an increasingly important standing, in 1892 and 1898, in the factories of Armentières and Boulogne-on-Seine, in 1907, in a private mansion in Auteuil, and afterwards in his constructions for the national railway. Louis Bonnier, who implemented it in 1911 for the lintels, floors, and staircases of the school complex of the rue de Grenelle, reserving brickwork for the façades, made use of it on a large scale in 1922 and 1923 in the great nave of the swimming pool built at Butte-aux-Cailles. At the same time, Charles Plumet made the judicious choice to use it for the new metro stations. Tony Garnier who, already dreaming of reinforced concrete in the shade of the Villa Medici, was able to construct some of his grandest designs out of this material, as part of the major works of the town of Lyon. The