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Joined: Oct 2000
Posts: 2,749
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Please see 300.11(A)(1)

Question from the field:

What is a fire-rated floor–ceiling or roof–ceiling assembly?


Joe Tedesco, NEC Consultant
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Take a look at the UL orange book and you will find thousands of them. [Linked Image]


Ryan Jackson,
Salt Lake City
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Thank you Ryan, I don't have that book here at my class. Can you give me a short summary of a typical ceiling?

[Linked Image]


Joe Tedesco, NEC Consultant
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No, Joe, Ryan cannot. Ceilings described in the UL Orange Book are tested as complete assemblies, for a specified period. There are any number of variations....wood frame, metal frame, exposed frams, under load, etc.

Sometimes a suspended ceiling is part of the assembly, sometimes not.

It's really an topic that can't be addressed without prints to look at, and a known structure to compare.

Joined: Oct 2000
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Thank you, I should have looked at Annex E for this information instead.

I imagine that the building designer or architect would have to provide the necessary information for the plan reviewer.

reno, when was the last time you inspected or installed wiring systems or equipment in the space identified by this thread concerning the question I asked.

I think that many of the spaces above the ceilings in many buildings is woefully in violation of Article 300 and Chapter 7 and 8.

Ain't that right, JC, JS, JS, and ME, etc.?

I have some pictures somewhere from back in 1981-85 from where I worked once!

I think a field trip and inspection to any office occupancy would find some surprises.

[Linked Image]


Joe Tedesco, NEC Consultant
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Actually, Joe...on second look, your question isn't a bad one!
As worded, the code would seem to ban attaching anything anywhere to a ceiling, obove a suspended ceiling, etc....in the field there is simply no way to know exactly what the conditions of the tests were.
I don't think that the code intended to ban, say, attaching EMT to the framing members. I think they meant to say "don't hang your stuff from ceiling wires where the suspended ceiling is part of the fire-rated structure."
The code saying one thing, while meaning another....like that's never happened before!

There is also the matter of enforcement; this code requirement isn't all that old, and you typically have no way of telling when something was built, or modified.

I suppose the real question is: how can you tell if the suspended ceiling is part of the fire-resistive assembly, and not meerly decorative?
For that, you might look for clues such as:
- lengthwise irregular cut-outs on the t-bars. These are there to cause the ceiling to deform in such a way as to continue to hold tiles in place;
- ceiling tiles made of gypsum, and coated on the back with foil (rather than vinyl-faced fiberglass);
- T-bars of extroadinary height, and with lots of tie-wires; and,
- Sheet-rock 'boxes' around light fixtures.

As if the situation wasn't complicated enough, in some area there are seismic requirements- and it can be hard to tell just why something 'extra' was done.

And, to make matters worse, there can be enormous differences between what the code requires, and what the designer intended. The World Trade Center being a case in point- it was built far in excess of, and designed for mis-haps unimagined by, any code requirements. (It is to the designers' credit that the towers behaved as well as they did!)

Here's some good news...If a suspended ceiling is being used as a return air plenum, you can be pretty sure it isn't part of a fire-rated asembly!


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