Head of wall detail at fire barrier wall

[DJ4827]

I was wondering what you might think about the required detail for a head of wall joint at a fire barrier wall in the following case. The code is 2009 IBC. The project has M and S2 occupancies, with some of the S2 separated with a 2hr fire barrier wall. Construction is Type V-B, so there is no general requirement to rate the roof-deck assembly. The M has steel trusses with 2X6 C.J.s and a plywood deck. The separated S2 has open web steel trusses. The trusses don’t penetrate the fire barrier wall on either side, nor would the C.J.s. The question is whether the plywood deck can continue over the top track of the fire barrier wall, and the open web trusses over the S2, or not.

One way of looking at this would be to say that the plywood deck is a burn-through opportunity, and the fire barrier wall therefore has to terminate at a 2 hr head of wall joint. Achieving this would require a rated roof/deck assembly. Or, one could say that since the wall has to be fixed to the deck, then the deck may be is “supporting construction” and has to be rated the same as the wall.

On the other hand, neither the code nor the commentary actually say this with any degree of clarity, and one of the diagrams in the commentary for 707.5 shows a fire barrier with an unrated unrated roof assembly on one side, and a rated assembly on the other, achieved with a dropped ceiling. So the commentary authors seem to accept that a fire barrier can terminate at an unrated roof. If so, then the continuous plywood deck would presumably be OK.

The applicable code clauses seem to be these:

707.5 Continuity. Fire barriers shall extend from the top of the floor/ceiling assembly below to the underside of the floor or roof sheathing, slab or deck above and shall be securely attached thereto. Such fire barriers shall be continuous through concealed spaces, such as the space above a suspended ceiling (the commentary adds that the floor/ceiling assembly at the bottom of the wall must be rated, but it does not say that the roof/deck must be rated).

714.1 General. Joints installed in or between fire-resistance-rated walls, floor or floor/ceiling assemblies and roofs or roof/ceiling assemblies shall be protected by an approved fire-resistant joint system designed to resist the passage of fire for a time period not less than the required fire-resistance rating of the wall, floor or roof in or between which it is installed (does not seem to address joints between rated and unrated construction).

707.5.1 Supporting construction. The supporting construction for a fire barrier shall be protected to afford the required fire-resistance rating of the fire barrier supported (can't find a definition, but the commentary seems to consider "supporting construction" to be what is under the fire barrier wall).

What would you require in this situation? Wood deck can continue over the top of the fire barrier wall? Or, the roof on at least one side of the fire barrier must be 2 hr rated, so there can be a UL listed HoW joint? Or maybe I missed something else?

Thanks

 

[Builder Bob]

If the two hour fire barrier terminates at the roof deck, the intent of the code has been met...... Nothing in the code requires "special" consideration for a rated wall intersecting a non-rated ceiling. The Metal Building Manufacture Association used to have some insurance bulletins that were very informative. It has been a few years since I have looked at the website so i don't even know if they still provide them or if they now charge a fee to see them.

Fire Walls (True Fire Walls) would have special considerations.

 

[cda]

not an expert but I do not think you have a problem, as long as there is no void space above the plywood.

The rated wall is giving the seperation, and is rated on both sides to the deck.

edit: what Bob said

 

[tmurray]

...and a plywood deck....707.5 Continuity. Fire barriers shall extend from the top of the floor/ceiling assembly below to the underside of the floor or roof sheathing, slab or deck above and shall be securely attached thereto. Such fire barriers shall be continuous through concealed spaces, such as the space above a suspended ceiling (the commentary adds that the floor/ceiling assembly at the bottom of the wall must be rated, but it does not say that the roof/deck must be rated).

You answered your own question. The burn through time of the plywood, considering the exposure cross-section is likely longer than the rating of the wall itself.

 

[DJ4827]

That is what I thought. But the reason I posted this was an article I read in the ICC's Online Building Safety Journal that discussed MBMA testing with UL regarding the HOW joint, and it seemed to me that it was saying that although the code wording in 714.1 addresses joints between rated walls and rated roofs, 714.1 is "commonly interpreted" to apply also to joints between un-rated roofs and rated walls. Because there is no UL listing for a HOW joint, if the roof is not rated, this creates a problem. As I initially read it, the outcome of the MBMA interaction with UL on the issue was some new UL systems all of which accepted the need for a tested HOW joint, and all of which have metal decks. But I missed that the MBMA got an interpretation from the ICC (34-08) that says what you said.

The article is here.

bsj.iccsafe.org/june/features/how_test.html]ICC BSJ Online: Head-of-Wall Joints in Metal Building Systems