The continuous slab constitutes a self-contained floor system, thought it may be desirable for non -structural reasons to add a separate top surface and
separate ceiling below. Before the development of the reinforced-concrete slab, the nearest equivalents were the floor composed of beams of timber or stone set immediately alongside one another, and the floor provided by a more or less solid fill above a brick or concrete vault. the first of these involved a very extravagant use of material and hence expenditure of effort, so it usually gave way to a more differentiated form with increasing skill in construction. The second was more efficient, inherently strong, and fireproof,and continued to be use for these reasons until supplanted by the reinforced-concrete slab. But it had the drawbacks of greater overall depth than alternative forms, and of greater weights plus the generation of outward thrusts, so that stronger walls were called for.