Pipe Grid Layout for space with very low ceiling

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I'm designing a pipe grid layout for a basement space below an existing theatre. The coffered concrete ceiling is between 7'-6" to 9'-0" clear to the floor. The grid will be installed professionally by a theatrical rigging company.

There's no question that I am asking for a 1.5" ID Schedule 40 grid, and the presumption is that all lighting fixtures will yoke up or overhang as much as they can. There will be vertical space between the ceiling coffers to allow this in most areas (the grid will be just below the coffered beams). I will probably ask for installation using speedrail (or its equivalent) so the entire grid can be at one consistent elevation (instead of the US-DS pipes sitting above or below above the SL-SR pipes).

My inclination is to specify a standard 4'-0" x 4'-0" grid module, but I am entertaining possibly tighter pipe centers, say 3'-0", which might (or might not) make things more flexible and I wonder what people think about that. I'm also curious if readers have anecdotal comments about whether there should be a pipe on the space's centerline, or if the grid should split center so a yoked fixture can actually have its lens on center.

Finally I have an idea about stopping the grid short of the walls of the space to allow overhung fixtures at the end of the grid to light a backdrop (for example) mounted to a wall. I wonder if people have opinions about doing so.

Many thanks for the ideas....

 

[Skervald]

I'm shooting from the hip here but I'd make a detailed drawing of your ceiling including the coffers and then one at a time overlay a 4x4' and then a 3x3' grid. Depending on the size of your coffers, you might find that one or the other option will align more pipe in the open spaces allowing you to yoke up more fixtures. You might also find an alternate spacing works better. Of course, the best way to know what you should do is to install it and then live with it for a few years. At that point you'll be an expert. I can't tell you how many times I've wanted to go back and kick my past self for not doing something a certain way.

 

[BillConnerFASTC]

You don't need speed rail or such for flat grids - they just shop fabricate the crossings and splice in the sections. Pretty easy to make up a lot of crosses in a jig and pre-cut a lot of the intermediate straight sections.

As far as elevation, it would depend on the pan (coffer) depth. I might just "strap" the grid to the bottom of the webs. All particular to a lot of specific details, and don't forget distro, where conduit runs, and where the plug boxes mount. Likewise, fire sprinklers, fire alarms, and of course HVAC. I think you could find organizing and coordinating these is a much bigger Challenger than the pipe grid layout.

As far as pipe center or bay center, I like to leave the center open so I can fly a chandelier or other necessarily center item as high as possible. I can always mount a light there with a piece of pipe and clamp(s), I can't always remove a section of grid.

I think grid module is not important. I might try to make sense of concrete pan layout. It seems with 4 x 4 it's not hard to get a light anywhere with a side arm. I have done anywhere from 3' to 6', and not always equal in both directions.

The back drop issue is hard to visualize but unless the space is very wide, it seems that you need to get lights on performers that just "scrapes" across audience - a very low angle. Again, without drawings and details, hard to say generally.

Good luck!

 

[rwhealey]

You may have discussed this project with an engineer already, but your existing conditions would be worth a look by a structural engineer if you haven't. if your slab above is post-tensioned you may have limitations on the locations the contractor can put hangers due to the tensioning cables, which would affect your grid spacing. It is possible to drill into a post-tensioned slab, just a bit more complicated than a cast-in-place slab with normal rebar.

 

[Footer]

Why not build boxes that actually sit inside the coffer opening tight to the ceiling instead of below it? You won't have neat pipes but might be a bit more flexible. Overhanging by default is a real pain and a big time suck. You also have to tightly anchor those pipes to prevent pipe spin.

 

[BillConnerFASTC]

Why not build boxes that actually sit inside the coffer opening tight to the ceiling instead of below it? You won't have neat pipes but might be a bit more flexible. Overhanging by default is a real pain and a big time suck. You also have to tightly anchor those pipes to prevent pipe spin.

I thought same - but dependent on coffer size. Working on one now with the pan space (the recessed or coffer area) around 30" x 66", and I could see insetting short battens - maybe two long or three short - 2-4" below the slab, though depth of pan would affect this. Also the anchor is in shear, rather than tension, which is simpler. Very detail specific. I still think the other stuff has a more consequential impact. I've never not been able to hang a light, but a duct or fire sprinkler has sometimes been an insurmountable obstruction.