A ceilings is an overhead interior surface that bounds the upper limit of a room. It is generally not a structural element, but a finished surface concealing the underside of the floor or roof structure above.

A cathedral ceiling is any tall ceiling area similar to those in a church. A dropped ceiling is one in which the finished surface is constructed anywhere from a few inches to several feet below the structure above it. This may be done for aesthetic purposes, such as achieving a desirable ceiling height; or practical purposes such as providing a space for HVAC or piping. An inverse of this would be a raised floor. A concave or barrel shaped ceiling is curved or rounded, usually for visual or acoustical value, while a coffered ceiling is divided into a grid of recessed square or octagonal panels, also called a lacunar ceiling. Ceilings have frequently been decorated with fresco painting, mosaic tiles and other surface treatments. While hard to execute (at least in situ) a decorated ceiling has the advantage that it is largely protected from damage by fingers and dust. In the past, however, this was more than compensated for by the damage from smoke from candles or a fireplace. Many historic buildings have celebrated ceilings, perhaps the most famous is the Sistine Chapel ceiling by Michelangelo.

The ceiling is an often-overlooked surface in the cleaning environment primarily because of the perception that ceilings are too difficult or impossible to clean.  Some building managers feel that simply painting the ceiling is faster and easier than any cleaning process.  A basic understanding of ceiling surfaces is critical for deciding the best technique for restoring the "clean" look to the surface. Most ceilings fall into one of several categories. Acoustical (acoustic) Ceiling - This ceiling type is the most common found in commercial buildings and in most office areas.  It is porous and basically appears smooth with small pinholes and crevices.  The primary function of all acoustical tile is for sound control.  There are, however, many types of acoustical tile, each with unique functions. Glacier - This ceiling is constructed of acoustical ceiling material. However, it looks much like icicles. Glacier ceilings must be sprayed with ceiling cleaning solution from four different directions to assure complete coverage of the surface.  Popcorn - This ceiling is sprayed onto a previously existing non-acoustical type ceiling already in existence.  The result is a stucco-like surface.  The disadvantage of this system is that if a stain occurs, there is no tile to replace it. Burlap - Burlap is very similar to acoustical ceilings.  However, it has a greater tendency to absorb dirt directly into the fiber making it difficult to clean the tiles with one cleaning. Vinyl-wrapped sheetrock - This is normal sheetrock or wallboard painted with enamel, latex or flat paint.  The enamel and latex paints allow the spray/wipe technique to be used.  Flat paint ceilings should be repainted when they become soiled since the flat paint can be removed with mild agitation or detergents. PVC (Plastic, Vinyl) Ceiling Tiles Ceiling tiles waterproof, mold, mildew and bacteria resistant, impact damage resistant, fire rated for kitchens, easy to install and maintain only requires soap and water to clean out lasts all other tiles. Corn Based Ceiling Tiles Ceiling tile prototypes made entirely of corn based, bio-degradable plastic. Keratin Based Ceiling Tiles Plastic made from Keratin, a substance derived from chicken feathers. Ethanol Based Ceiling Tiles Using ethanol as a feed stock for vinyl is not a new concept, though until recently the economics have not been practical. Thermal Ceiling Tiles Thermal Ceiling Tiles basically are tiles with a thermal barrier for protection from above the ceiling a 15 minute proof is usually standard. Drop or Suspended Ceiling (Tiles) A ceiling suspended (dropped) grid system by hangers (wires) with standard ceiling tiles (Armstrong, USG, Celotex, Ceilume, PVC) of 2' by 2' or 2 by 4' to cosmetically cover a/c ducts, wiring, etc as well insulating from up ceiling for fire protection, reduction in a/c bills, etc. Cleaning or Painting Acoustic or Porous Ceiling (Tiles) Acoustic or Porous Tiles are traditionally made of wood or mineral fuber and are no more than a paper product, hard to clean, water spots can only be removed by painting which can cause you to lose your fire rating and have issues with the fire marshall and your insruance company. Health Department issues will be with the mold that grows in Acoustic tiles. Customer issues will range from a nasty looking ceiling or one sagging to those who will be bothered by the mold in your ceiling. Cleaning or Painting Non Acoustic or Non Porous Ceiling (Tiles) Other than PVC, Ceramic, or Steel all other tiles may be cleanable for a while until their vinyl coating either peels off or wears. Painting may cause issues with Health Department and Fire Marshall check with manufacture, health department and fire marshall before doing so . Myths Acoustical levels (NRC) for acoustical tiles remain the same, not true for most what makes them acoustical are the holes in them, once they start filling with dirt and dust the NCR levels drop. Tiles treated to handle humidity will last a long time, at best 10 years and that is if you are not in an extreme humid area or do not have major leaks. These tiles can cost as much as 4 times normal tilels. You are better off with PVC, Ceramic or Steel tiles. Tiles treated to handle Mold and Bacteris will last a long time, warranties on most are good as long as the tiles do not get wet, moist or damp meaning as long as they are dry. You are better off with PVC, Ceramic or Steel tiles. Hour rated tiles will give protection in a fire, FALSE, most were tested with a metal grid assembly and after 1-3 hours the test showed the grid still there so gave the tiles an hour rating even though they were gone much, much sooner. The best protection for barrier is either Steel or Concrete and a sprinkler system installed correctly no less than 1 head per 100 sq ft . PVC off gasses, somne does, the new car smeell is PVC, Shower Curtains are PVC, Most PVC Ceiling Tiles such as Genesis have absolutely no odor to them.