A false ceiling is often a secondary ceiling, hung below the main (structural) ceiling. It may also be referred to as a drop ceiling, T-bar ceiling, false ceiling, or suspended ceiling, and is a staple of modern construction and architecture. The area above the dropped ceiling is called the plenum space, as it is sometimes used for HV AC air return. The plenum space is also very commonly used to conceal piping, wiring, and/or duct work.
A typical dropped ceiling consists of a grid-work of metal channels in the shape of an upside-down “T”, suspended on wires from the overhead structure. These channels snap together in a regularly spaced pattern – typically a 2×2 or 2×4 foot grid in the US, or 600×600 mm grid in Europe (this is the modular size of the grid, the tiles are actually 595mm x 595mm or 595mm x 1195mm). Each cell is filled with lightweight “tiles” or “panels” which simply drop into the grid. Tiles can be selected with a variety of materials, including wood, metal, plastic, or mineral fibres, and can come in almost any color. Light fixtures, HV AC air grilles, and other fixtures are available which can fit the same space as a tile for easy installation. Most tile material is easily cut to allow fixtures in other shapes, such as incandescent lights, speakers, and fire sprinkler heads.