Acoustical Ceiling Supporting Insulation

[CBSE]

Has anyone ever been asked to justify adding insulation on top of a suspended acoustical ceiling grid? The code allows for 4 psf prescriptive loading to the suspended ceiling attachments systems. Adding insulation is like another .75 psf. An architect I do a lot of work for asked if I could justify this for him. He didn't like me saying put the insulation somewhere else!

 

[wannabeSE]

Is this an existing ceiling or new. I don't think all systems can handle 4psf. The main runners on a light-duty system are good for 5 plf with a 4' span and L/360 deflection (see ASTM C 636). This would be equivalent to 1.25 psf when hangers are at 4'OC each way. Perhaps the 4 psf allowable load is when a heavy-duty system is specified.

I strongly dislike (trying to be polite) insulation on the lay-in ceiling, but none of my reasons are structural. It should be fairly easy to check the ceiling once you know what is (being) installed. Note: ASTM C 636 defines light, intermediate and heavy duty systems.