# Understanding how dropped ceilings are constructed



## village_idiot (Nov 26, 2012)

I'm brand new to construction. Never seen a single story dropped ceiling plenum before.

Imagine you have 10' high office ACT 2x2 dropped ceiling, and a 14' high building roof so a 4' plenum space, and it's a single story building. Would the office walls typically go 14' all the way to the concrete roof plane, or would they only go up 10' and the dropped ceiling sit on top of them, or would they go up something like 11' for the dropped ceiling to be secure in them, but not all the way to the roof? :confused1:


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## MarkWood (Oct 8, 2010)

Only firewalls go all the way to the roof. I dont put the ceiling on top of the walls because you have an unfinished sheetrock edge that you can see. just build the walls tall enough so you can screw the wall angle to the wall.


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## ScipioAfricanus (Sep 13, 2008)

that might depend a lot on how the partition walls are being constructed and are they steel or wood stud or something else?

Is the drop ceiling in yet? Do you have to install everything? Can you do what you are tasked with doing?
So you need a detail? Do you need to brace the tops of he walls to the purlins or roof beams?

Andy.


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## village_idiot (Nov 26, 2012)

No worries Andy, I'm a fire sprinkler design student, playing around with Autodesk Revit. I was given a 2D Autocad plan and given some limited information: It's a single story office building, with a dropped ceiling at 10' and a roof at 14'. The heights of the office walls are whatever I want them to be I guess (above 10') because it's not a real project, but I was trying to discover what it would probably be in reality. 

Thanks for your help guys!


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## GCTony (Oct 26, 2012)

V Idoit,

When new office buildings are designed and built, the common area walls (corridors, mechanical rooms, stairwells, restrooms) are usually built from the floor to the structure above. The ACT ceilings, are usually installed complete throughout the future tenant spaces even if no tenant will be occupying the space. Lighting, HVAC grills, sprinklers, exit/egress lighting are installed in a standard "pattern". When a tenant rents the space and builds out, partition walls are constructed to the bottom of the ACT ceiling. Many building owners don't allow tenants to break the ceiling grid. The tops of the drywall partitions are finished with zip or L bead.


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## jadleybray (May 2, 2008)

Codes are different everywhere but here's a few things I've run into lately. 

Is the above ACT space a plenum/ and or corridors plenums? If so, all materials will need to be plenum rated/fire & smoke per your code.
Code may state drywall must be 6" min above ceiling.
Medical facilities may require full heigth drywalled walls for privacy concerns.

As you know, tall walls will affect your sprinkler layout in the above ACT areas drastically.


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