Structural penetrations @ rated shaft wall

[Examiner]

Stair shaft is rated for 1-hour in a two story building Type II-B construction. Have to do an enclosed stair due to security and owner’s wishes. Stair is L-shape.

The roof structure penetrates and is continuous through the stair and its shaft walls.

Is any fireproofing required at the penetration and/or around the roof steel? Will fireproofing be required beyond on the roof steel beyond the stair’s perimeter rated walls? Input please.

 

[Coug Dad]

What is holding up the one hour walls at the second floor? The one hour walls must be supported by one hour structure which is difficult in Type II-B construction. The floor and roof structure should be one hour rated to at least the adjacent bay.

 

[mtlogcabin]

Section 712

 

[Examiner]

Section 712 only addresses penetrations such as conduit and related mechanical penetrations. It does not specifically address structural steel. I have even read the commentary to this section and it does not appear to address structural steel penetrations.

The shaft walls are 8" cmu and are not supported on or bearing on the second floor.

 

[Coug Dad]

Ideally, the roof over the stair enclosure should be structurally separate from the roof over the rest of the building. Then the penetrations are not an issue.

 

[Examiner]

The structure is to be a pre-engineered metal building. I talked to code congress and did not get a good answer. It appears to them it is not addressed in the code. The Section in Chapter 10 just addresses penetrations are not allowed if not serving the stair. I know this is condition existing in most every stair that has walls going to the roof deck. If the stair's roof is not bearing on the shaftwall what do you do about the penetrations of the steel roof joist?

 

[mtlogcabin]

I believe you meet 706.5. You could ask for compliance with 707.12 Enclosure at the top but I do not think that is required for what you describe.

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.

 

[texasbo]

I too think you comply with 706.5, but you also have penetrations of the shaft before it reaches the roof deck or slab. Penetrations shall be protected per 712 with a through penetration firestop system.

 

[TJacobs]

Put a one-hour lid under the roof structure at the top of the stairwell...no exposed steel.

 

[Coug Dad]

TJacobs, I have gotten that approach approved many times as a code alternate. Prescriptive code requires stairs to be enclosed in fire barriers and a horizontal lid is not permitted as part of a fire barrier assembly. It does seem reasonable to me though.

 

[TJacobs]

Coug Dad, I agree it's not spelled out. Just says fire barriers to the roof deck. The way I look at it, when was the last time you saw fire barriers properly constructed around a maze of structural steel? I'll take the lid using 706.5 Exception 2 leading you to 707.12.

 

[mtlogcabin]

It is spelled out. Remember the 2003 defined a fire barrier as a verticle and/or horizontal assembly

707.5 Continuity.

Shaft enclosures shall be constructed as fire barriers in accordance with Section 706 or horizontal assemblies constructed in accordance with Section 711, or both, and shall have continuity in accordance with Section 706.5 for fire barriers or Section 711.4 for horizontal assemblies as applicable.

707.12 Enclosure at the 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.