CEILING SYSTEMS CEILING SYSTEMSCeiling systems found in cleanrooms are the complex enclosure elements. The two most common systems are extruded aluminum grid with field-constructed plenum and modular prebuilt integrated plenum with grid. Both of these systems serve as the mounting for terminal filtration (HEPA or ULPA) or FFU and lighting. The ceiling system also may be supported from freestanding walls or columns or suspended from existing structure. The factors involved in the selection of the ceiling system are typically site specific depending on required free span, available vertical volume, access, and load carrying requirements.