Finish ceilings serve several functions including visual, light and sound control, and concealing mechanical, electrical, and plumbing systems. There are several types of ceilings including exposed structure, tightly attached, suspended, and interstitial. Suspended ceilings are hung from the structure using wires or metal framing and allow for a plenum space above for ducts and pipes. They provide access for maintenance and are widely used with lay-in panels and grids. Interstitial ceilings are common in hospitals and laboratories to accommodate extensive mechanical systems while providing access.