Pipe resting on top of trapeze

[FIVE50]

Running pipe under duct work using trapeze hangers.. to achieve required height above ceiling, we need to have pipe on top of trapeze hangers. I have seen this before but never have had to use this method. Is this allowed per NFPA? Thank you for your help.

 

[UFT12]

Unless the duct width is more that half the allowable distance between sprinklers, better have the head pendent and right next to duct and almost flushed with the underside. This way no pipe running under duct hence better clearance and no expensive and laborious trapeze needed.

 

[FIVE50]

Yes, that is definitely the better option, but does anyone know if you are allowed to run on the top of trapeze hangers?

 

[skdesigner]

No issues that I'm aware of. The section modulus tables for trapeze hangers in NFPA 13 are developed on the assumption that the concentrated load occurs mid-span of the trapeze member. The point load would be at the top of the trapeze member regardless of whether it was a split ring or nut/washer supporting a hanger below, or a piece of pipe sitting on top of the trapeze member. I would probably lean towards angle iron or unistrut in that situation, as it would be quite a bit easier to secure the branch line piping.