Roof Member Penetration of Stair Enclosure

[Tdgdesign]

Hello All,

I am new here and excited to have found this forum!

So, I am a member of the design team for a 2-story, Type 2B pre-engineered steel building. We are having an issue with stair enclosure - specifically how to avoid penetrating the top of the enclosure with our roof purlins. Our Fire barrier walls run to underside of metal B deck. Configuration of stairs make it extremely difficult to head off roof purlins to avoid enclosure. Can we use the assembly I501 attached to the underside of roof purlins - essentially making our own rated ceiling assembly over the enclosure?

Thanks in advance!

Cheers

UL Design No. I501 [h=2] Unrestrained Assembly Rating - 1 Hr Load Restriction - Limited to the Dead Weight of the Assembly.[/h] [h=4][/h]

1.

Perimeter Channels —

Used to support steel studs at both ends of wall structure. Min. 6 in. deep with min. 2 in. legs and formed from min. No. 20 MSG galv. steel (0.0329 in. thick bare metal thickness). Perimeter channels attached to wall structure with fasteners spaced not greater than 24 in. O.C. at both the top and bottom of the vertical leg. Maximum clear span from vertical leg to vertical leg of the perimeter channels is 8 ft., 2-1/4 in.

2.

Steel Studs —

Min. 6 in. wide with min. 1-5/8 in. legs containing folded back flanges and formed from min. No. 20 MSG galv. steel (0.0329 in. thick bare metal thickness). Studs to be cut 1/2 in. to 3/4 in. less than the clear span between the vertical legs of the perimeter channels. Studs spaced a max. 16 in. O.C. At each end of the stud, the un-faced side shall be secured to the perimeter channel with one 1/2 in. long pan-head steel screw. Studs are used at each end of the horizontal barrier to terminate the assembly at the adjoining wall. These end studs shall be secured to the adjoining wall in the same manner as the perimeter channels (Item1).

3.

Steel Strap —

Min 4 in. wide formed from min. No. 20 MSG galv. Steel (0.0329 in. thick bare metal thickness). Secured perpendicular to the studs at the centerline of the span using two 1/2 in. long pan-head steel screws. Strips to overlap one full stud bay at splice locations. As an alternate to the steel strap, Perimeter Channels (Item 1) may be substituted and installed in the same manner as the steel straps. If a continuous piece is not used, the abutted legs are installed on each side of the centerline of the span and overlap one full stud bay.

4. Gypsum Board* —Three layers of nom. 5/8 in. thick, 46 to 54 in. wide, gypsum board installed with long dimension perpendicular to the steel studs. Base layer installed with end joints in adjacent rows staggered min. 32 in. Boards secured to studs and perimeter channels with 1-1/4 in. long Type S steel screws spaced max. 16 in. O.C. Middle layer installed with end joints in adjacent rows staggered min. 32 in. Boards secured to the studs and perimeter channels with 1-5/8 in. long Type S steel screws spaced max. 16 in. O.C. Middle layer joints staggered a min. 16 in. from base layer joints Face layer installed with end joints in adjacent rows staggered min. 32 in. Boards secured to the studs and perimeter channels with 2-1/4 in. long Type S steel screws spaced max. 12 in. O.C. Face layer joints staggered a min. 16 in. from middle layer joints.

 

[Builder Bob]

You need to talk to the AHJ.....

 

[Tdgdesign]

Well thanks Bob but I was curious to see what people here thought before talking to the AHJ.

 

[Chris_Sanders]

OK, I'm not a code guy but I'll take a stab at it.

I'd be concerned that if you attach gypsum board to the bottom of the purlins that'd be fine for the ceiling...but you wouldn't have a 1-hour vertical barrier from the bottom of the purlin to the bottom of the deck unless you also figured out a way to maintain that rating where the purlins penetrate your wall assembly. I'd also be concerned with deflection, but that's another matter.

I recently had a similar situation with an existing steel building, where zee purlins penetrated various rated assemblies. Worked with Hilti to identify which of their systems were closest to what we were trying to achieve, then got an engineering judgement from them based on our specific situation. Submitted this to the AHJ and was approved.

Hope this helps!

 

[mtlogcabin]

713.8 Penetrations.

Penetrations in a shaft enclosure shall be protected in accordance with Section 714 as required for fire barriers. Structural elements, such as beams or joists, where protected in accordance with Section 714 shall be permitted to penetrate a shaft enclosure.

You do not need to rate the top of the shaft if it goes to the roof deck. You can protect the purlin through penetrations as outline in 714 or install a rated ceiling. .

 

[Examiner]

The word pre-engineered building automatically causes concerns with multi-story buildings. The stair if a rated EXIT will have fire barrier walls. Fire barrier walls must be supported by the same rating as the EXIT Stair. Let’s say you are a two story building and your EXIT stair requires a 1-hour fire barrier wall. Then if you are using studs and bearing them on the 2nd floor the supporting structure of the floor must be 1-hour. That could mean taking the floor rating over the entire bay that supports the floor. As for the roof; if it is a pre-engineered roof with the R-value required using the vinyl back insulation you cannot get a proper fire seal at the top of the fire barrier walls. Therefore, you need a 1-hour cap over the stair. There are shaft wall systems that can be turned horizontal for short spans that could be used as the rated cap.

If you can get the design with an automatic fire suppression system to have an unenclosed Exit Access Stair then the rating goes away. An unenclosed Exit Access Stair is limited to story height usually two but the newer codes and occupancy use group may allow more than two.

The most common mistake I see in plan review is not providing the floor rating required to support the fire barrier wall. Not knowing the Code you are using I cannot quote you the required sections but look in the Fire Barrier section for Continuity.

 

[combo7]

I think he needs to protect the purlins with a fire barrier. I like the drawing.

Sent from my SM-N900P using Tapatalk

 

[steveray]

What code edition....I believe this is becoming more and more allowed (2012 and 2015) after we have been struggling for years to get people not to do it....

MT summed it up well...

 

[Examiner]

I think he needs to protect the purlins with a fire barrier. I like the drawing.Sent from my SM-N900P using Tapatalk

I do not think there is a UL rated system to protect roof purlins for pre-engineered buildings and the drawing is not a UL system for the horizontal condition. You cannot take a 1-hour wall and turn it horizontal and get the same fire rating. The horiziontal position gets hotter quicker then the vertical position. The fire barrier wall has to go to the underside of the roof deck. That cannot be done with a pre-engineered building due to the vinyl backed insulation and the required R-value for the roof. If the roof's insulation is on top of the roof deck then the fire barrier can go to the underside of the roof deck. However, that roof system would not be a pre-engineered roof then.

Oops looked up the UL I501 system and it is applicable for horz locations. Sorry.

 

[Tdgdesign]

Forgot to mention this building falls under the 2009 IBC - thereby not allowing for any structural penetrations. Our roof purlins will still penetrate the fire barrier walls above the rated ceiling. Anyone think it is possible to argue that the fire barrier ends at the intersection of the rated ceiling?

 

[steveray]

Forgot to mention this building falls under the 2009 IBC - thereby not allowing for any structural penetrations. Our roof purlins will still penetrate the fire barrier walls above the rated ceiling. Anyone think it is possible to argue that the fire barrier ends at the intersection of the rated ceiling?

What section of the 2009 IBC are you referring to? A reasonable AHJ may allow compliance with a newer code under "alternative compliance"....

2015 IBC

713.12 Enclosure at top.

A shaft enclosure that does not extend to the underside of the roof sheathing, deck or slab of the building

shall be enclosed at the top with construction of the same fire-resistance rating as the topmost floor

penetrated by the shaft, but not less than the fire-resistance rating required for the shaft enclosure.

Fire barriers shall extend from the top of the foundation or 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 space, such as the space above a suspended ceiling. Joints and

voids at intersections shall comply with Sections707.8and707.9. 707.9

Exceptions:

1. Shaft enclosures shall be permitted to terminate at a top enclosure complying with

Section 713.12.

2. Interior exit stairway and ramp enclosures required by Section 1023 and exit access

stairway and ramp enclosures required by Section 1019 shall be permitted to terminate at

a top enclosure complying with Section 713.12.

 

[Tdgdesign]

Just wanted to post a quick update. The AHJ accepted the design as illustrated here. Thanks for all your input everyone - this forum is a goldmine! Cheers!