Flooring Anatomy

Regardless of the material chosen as the top layer, the underlying structure of most floors similar. The most common type in residential construction is the framed floor. On a ground-level framed floor, the flooring rests on joists that sit on sills along the foundation and is often supported at a midpoint by a steel girder or wood beam.

An elevated framed floor like the one shown above is supported by beams that run perpendicular to the joists where the weight of the floor is borne by support columns. In most cases, the joists are tied together with bridging for extra stability and to keep them from moving from side to side.

Floor joists are covered with some form of sub- flooring, typically tongue-and-groove plywood, particleboard, or OSS (oriented-strand board). Depending on the type of flooring used, the subfloor may be covered with an additional layer of underlayment, such as cement board (see page 34). The top layer of flooring is installed on the underlayment or subfloor and usually rests on some type of cushioning layer such as roofing felt.