Fire Rating a Joist Cavity

[Code-Hound]

Is there a product that will give me a 1 hour rating in a joist cavity where we are running electrical cables ? We will have a normal 2hr horizontal assembly but the cable will obviously be on the other side of the rated ceiling gyp. The floor above has 1.5" of gypcrete, so, do I need to rate the cavity then ?

 

[Plumb-bob]

I have allowed 2 layers of 5/8" type x gwb on all 3 sides of the joist cavity in situations like this. The 1.5" of gypcrete will not get you an hour rating.

 

[Code-Hound]

I have allowed 2 layers of 5/8" type x gwb on all 3 sides of the joist cavity in situations like this. The 1.5" of gypcrete will not get you an hour rating.

That's what figured, thanks Plumb-bob.

 

[Inspector Gadget]

The 1.5" of gypcrete will not get you an hour rating.

Sort of off-topic, I'm assuming you're referring to an Appendix D (Canadian) calculation .... I might be persuaded to give it an extra five minutes as "concrete topping" per D-2.3.4-G.

Likewise, might the US Codes would allow gypcrete to have some kind of FRR?

(Note that I am not disagreeing with your assertion.)

 

[fw.]

You lost me. If you have a 2 hour rated horizontal assembly why would you need to individually rate the joist cavity? Firestop the wires where they penetrate the assembly per Section 714 and then they are protected by the assembly when they are in it.

 

[Code-Hound]

You lost me. If you have a 2 hour rated horizontal assembly why would you need to individually rate the joist cavity? Firestop the wires where they penetrate the assembly per Section 714 and then they are protected by the assembly when they are in it.

BO worried about heat build up from large feeder cables, 8-10 of them. If the fire starts in the cavity then the protection below is for naught I guess. This is in a building that just had a fire caused by one of these wires. Fire went right on through the horizontal chase they were in and took out 8 units !

 

[tmurray]

Yeah... I'm a little confused too.

If the horizontal service space is not required to be rated, that's kind of the end of the story.

BO is not allowed to enforce requirements around what they are concerned about, only what the code is concerned about.

 

[Plumb-bob]

Yeah... I'm a little confused too.

If the horizontal service space is not required to be rated, that's kind of the end of the story.

BO is not allowed to enforce requirements around what they are concerned about, only what the code is concerned about.

I agree with that. I was answering to how to rate a joist cavity if required, not the bigger picture of if the separation is required.

 

[Code-Hound]

If the fire starts in the cavity…it can go to floor above thus bypassing the 2HR ceiling …. Code officials can have final determination on certain things if possibility of repeat occurrence, especially since this building has had 2 fires already … both electrical

 

[tmurray]

If the fire starts in the cavity…it can go to floor above thus bypassing the 2HR ceiling …. Code officials can have final determination on certain things if possibility of repeat occurrence, especially since this building has had 2 fires already … both electrical

They certainly can, provided they lawfully introduce a building code amendment. There are even some gray areas of the code where the official is able to exercise their discretion. But what they absolutely cannot do is ad-hoc decide that something is required despite there being nothing in the code that addresses it.

They can certainly give a recommendation, but it would be just that. A recommendation. Not a requirement.

 

[Code-Hound]

So in the NEC Section 110, there is a somewhat vague handling of this subject. I am originally from the Northeast and would agree with you all that they cannot normally, willy-nilly require something not stated in the code, but apparently here in Indiana, when the code is somewhat "iffy", their discretion can become a requirement apparently. Thanks for all the feedback. This is my new favorite site .... so many supportive folks here with great input !