The function of stairs is to provide floor-to-floor access. They can be defined as a series of steps (combination of tread and riser), each continuous set of steps being called a flight. Landings may be introduced between floor levels, to break up a long flight giving rest points, or to change direction of the stair. Stairs can be classified according to their plan shape or by the material from which they are made. Timber stairs are common in dwelling houses, whilst concrete is most common for other purpose groups.
A typical timber flight consists of treads and risers, housed into strings, the outer one of which is is joined to newel posts. These support the handrails /banisters and balusters that protect the side of a flight and are collectively called the balustrade. The triangular space under a flight, called the spandrel, is often filled in to form a cupboard.