Sprinkler pipe hung from metal deck

[kc9508]

On a current project, we've gotten a request from the contractor to hang 1" diameter sprinkler piping directly from the metal roof deck using Sammy x-press anchors (expansion-style hanger installed from the bottom of the deck flute). We get these requests every so often on projects and usually refer to our steel deck specification prohibiting hanging loads from the deck. But I'm curious of other engineers' take on this. Do you sometimes allow light loads to be hung from the roof deck or always require they attach to a beam/joist?

 

[Ron]

Don't hang anything from the deck. Has both a structural implication and a roofing implication. Both negative!

 

[KootK]

We'll allow light loads to be hung from the deck and typically pass the request bank to the deck supplier for evaluation and approval. I would like to hear more about these roofing problems however.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[wannabeSE]

I assume the deck is B-Deck or similar with insulation and roofing above. We allow it. When we specify the deck, we include collateral loads for mechanical equipment and architectural components in the design. The hanger load from a 1" fire sprinkler is similar to the load from an acoustical tile ceiling hanger wire. Just make sure the deck has the capacity and there aren't too many other loads in the same.

 

[kc9508]

Thanks for the feedback. Wannabe - yes it is type b deck with insulation and membrane roofing above.

Ron - these anchors are installed in the bottom of the deck rib, so I believe the anchor head does not project above the top of the metal deck (keeping it below the insulation/membrane layer). Have you experienced roofing problems in the past with these types of anchors? Just curious what may have caused these issues.

 

[Ron]

kc9508....most of the roofing issues are related to deflection. Stretched deck spans are usually the culprit with the added load. Small pipes usually not an issue but large pipes and wet systems can be an issue.

Keep in mind that one trade's work has little or no respect for other trades. While membrane penetration is easy to avoid, we still see it occasionally. Be careful.

Other considerations....
Anchor/fastener corrosion from roof leaks and/or dissimilar materials
Expansion/contraction of pipes enlarging the hole in the deck