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 100 to 200 millimetres (4 to 8 in) is often needed between the lowest obstruction and the level of the ceiling grid. A direct-mount grid may work for those who want the convenience of a dropped ceiling, but have limited headroom. Stretch ceiling supports require less than one inch of vertical space, and no space is required for tiles to be lifted out with a stretch ceiling, but a greater clearance space may be chosen to allow room for MEC or for aesthetic reasons.
In older buildings the space above the dropped ceiling was often used as a plenum space for ventilation systems, requiring only enclosed ducts that deliver fresh air into the room below, with return air entering the ceiling space through open grilles across the ceiling. This practice is now used less frequently in new construction.
Effective building design requires balancing multiple objectives: aesthetics, acoustics, environmental factors, and integration with the building's infrastructure—not to mention cost of construction as well as long-term operation costs.
Another advantage of a dropped ceiling is that the easily removed ceiling panels offer instant access to the plenum, greatly simplifying repairs or alterations.