Dropped ceiling
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In construction and architecture, a dropped ceiling, also referred to as a drop or suspended ceiling, is used as a secondary ceiling formed to conceal piping, wiring, or ductwork, into an area called the plenum. Consisting 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 2x2 or 2x4 foot grid—and each cell is filled with lightweight "acoustic ceiling tiles" or "panels" which simply drop into the grid. Tiles can be selected with a variety of surface textures, and are typically white, but can be painted any color using standard latex paint. Fluorescent light fixtures of the same dimension, and incandescent lights are then installed into the grid, as desired.
The suspended ceiling was originally developed to conceal the underside of the floor above and to offer acoustic balance and control in a room. The acoustic performance of suspended ceilings has improved dramatically over the years, with enhanced sound absorption and sound attenuation. This is complemented by adding "sound batt" insulation above the panels to help deaden sounds and keep adjacent rooms quieter. If fire safety is a concern, ceiling tiles made from mineral fibres can be used to meet fire safety ratings. Many of them also provide additional fire resistance in order to meet the "time rating" or "fire rating" required by building regulations. Another advantage of a dropped ceiling is that the easily-removed ceiling panels offer instant access to the plenum, greatly simplifying repairs or alterations.
One disadvantage with this ceiling system is reduced headroom. Clearance is required between the grid and any pipes or ductwork above to install the ceiling tiles and light fixtures. In general, a minimum clearance of eight inches is often needed between the lowest obstruction and the level of the ceiling grid.
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