Roofs composed of a thick slab are a product of modernist technological achievement. Concrete and metal constructions enabled the covering of large spans without the use of loadbearing columns. Yet concrete slabs needed to be thick enough in order to resist the strains of extension. In other cases, the roof was built with metal trusses, creating a spatial structure of a certain height. Such truss roofs covered with metal veneer gave the impression of having a uniform slab. In other cases, parapets protrude over the edge of a roof as a cantilever created the impression of a thick roof hanging over a building.