Abstract: A plenum-type ceiling for a clean room is formed of modules having lateral side portions which are adapted to be attached together into a grid-like network. Bottom portions of the lateral sides of each module are inwardly stepped to provide downwardly facing recessed channels for the installation of lighting, fire extinguishing equipment and other facilities so that the ceiling is substantially planar and without facilities or lighting protruding therefrom. Inwardly and outwardly facing channels are also provided at the lower edge of the inwardly stepped portions of the sides in order to form an annular trough as a seal structure for mounting of air filters and air flow control devices. A bracket is also provided for suspension of objects such as partitions from outwardly facing channels in a manner which substantially eliminates entrainment of air near the ceiling and the avoidance of interference with the facilities.