I have heard several times (often from those outside fire protection) that sprinkler pipe should be located "wherever it can fit around everything else," or something to the effect of "the sprinkler contractor will figure it out."
It is under that same mentality that mechanical and electrical engineers will complain when the fire sprinkler contractor is first to installation and they now have to redesign portions of their ductwork or conduit runs.
Is it really the sprinkler contractor's fault if no one allocates space for sprinkler pipe in the first place?
Coordination often comprises the most difficult and commonly the most overlooked part of building systems design. Ideally, where should sprinkler pipe be located above a ceiling?
I've asked a handful of designers, engineers and installers for their take on what the ideal height of sprinkler pipe is to effectively coordinate with other systems while minimizing extra pipe. While each project will vary in detail, much of the consistent thought has been to locate fire sprinkler pipe above the top plane of lay-in lights and underneath ductwork while routing to avoid can lights and slot diffusers (which tend to be deeper than lay-in light fixtures). The lower the sprinkler pipe, the less pipe required to create the drops down to each sprinkler.
In my experience (and as others have concurred), locating the pipe centerline 8-inches above the finished ceiling often works well. Under this location it is still important to avoid routing over the centerline of light fixtures, or over diffuers, deep can lights, and slot diffusers. While LED lights have helped keep the depth of lay-in fixtures to less than older fluorescents, it is still important to avoid the centerline of lights as to avoid the fixture hangers. Greater depths or conflicts with any of these elements can of course raise the centerline up to 10 or 12-inches above the finished ceiling.
That being said, the ideal height of sprinkler pipe can be impacted by two other concepts: concealed space protection and seismic bracing. Where concealed spaces need to be protected (such as in combustible construction applications), it may be worthwhile to raise the pipe closer to the underside of the wood structure.
Another important consideration is when seismic bracing is required. Where there is a significant distance between the buildings' structure and the pipe, seismic bracing begins to lengthen and as a result must have greater reinforcement (larger pipe diameters for lower slenderness ratios). In these scenarios, it can be easier to shorten the bracing lengths by raising the system closer to the height of structure.
Regardless of where pipe is to be located, establishing space for sprinkler pipe early in a project is a benefit to both upfront engineers and contractors on the back end.
What is your routing preference? Have you found any height to be more ideal than others? Feel free to comment if so.
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Joe Meyer, PE, is a Fire Protection Engineer out of St. Louis, Missouri who writes & develops resources for Fire Protection Professionals. See bio here: About