For typical ductwork (general commercial), about 4 psf (19.5 kg/m^2). Add about 3 psf(14.6 kg/m^2)for ceiling tile and grid. For lights/electical, another 2 psf (9.8 kg/m^2).
You may convert to other forms for ease of computation.
We use about the same as Ron....a little lighter. In most office/warehouse applications, we've found 5 psf (24.4 kg/m^2) to apply for ductwork and lighting. For ceiling tile/grid we use 2 psf (9.8 kg/m^2). In heavier mechanical rooms, where numerous pipe hangers and larger ducts may occur, we sometimes increase the load to 30 psf for mechanical/electrical (146 kg/m^2).
