Ceilings are classified according totheirappearance or construction. A cathedral ceiling is any tallceilingarea similar to those in a church. A dropped ceiling is oneinwhich the finished surface is constructed anywhere from afewinches or centimetres to several feet or a few metres belowthestructure above it. This may be done for aesthetic purposes,suchas achieving a desirable ceiling height; or practical purposessuchas acoustic damping or providing a space for HVAC or piping.Aninverse of this would be a raised floor. A concave orbarrel-shapedceiling is curved or rounded upward, usually forvisual oracoustical value, while a coffered ceiling is divided intoa gridof recessed square or octagonal panels, also called a"lacunarceiling". A cove ceiling uses a curved plaster transitionbetweenwall and ceiling; it is named for cove molding, a moldingwith aconcave curve.[1] A stretched ceiling (or stretch ceiling)uses anumber of individual panels using material such as PVC fixedto apermieter rail