# 1 Hour roof ceiling assembly in existing building



## imasayer (Jan 18, 2021)

Good day folks,

Long time reader, first time poster so please forgive me if I am putting this in the wrong place or if this information has been covered before.  Did a search but couldn't find anything.

I am currently working on a tenant improvement project in a 3 story building.  The stairs were never rated.  We are replacing the doors and the walls are cmu, so no issue there, but I am struggling with the roof/ceiling assembly.  The problem is that I don't know what the roof assembly is between the steel deck and the single ply membrane.  Every UL assembly I can find requires gyp or cement board over the the steel deck.  Anyone aware of a 1-hour assembly that does not require this?

What I know about the assembly is: 3' steel trusses @ 60" O.C., 1 1/2" steel deck, some amount of some kind of insulation, and single ply membrane.

The building is 3- story, 34,000 sf, B & A-3 Occupancy (non-seperated)

Thank you for any help! (and for all the help I have found in the past!)


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## RLGA (Jan 18, 2021)

Question #1: Why do you need to know the roof assembly construction?

Question #2: What is the existing construction type?

Question #3: Is the total building area 34,000 sq. ft., or is that the floor area of the largest story?

Question #4: What percent of the story area is the Group A-3 occupancy?

As for finding out about the roof assembly, you can have a core sample taken by a roofing consultant/contractor or the manufacturer of the roofing membrane. If the roof is still within warranty, the roofing membrane manufacturer may have the details of the roof assembly in their records.


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## cda (Jan 18, 2021)

Well it’s about time 

Welcome


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## imasayer (Jan 18, 2021)

RLGA said:


> Question #1: Why do you need to know the roof assembly construction?
> 
> Question #2: What is the existing construction type?
> 
> ...


Hi RLGA,

Because all of the 1 hour roof/ceiling assemblies I find require gypsum board or cement board over the steel deck.  Looking for help on this question specifically.

#2 - Type II-B construction. Sprinkled.
#3 - Total building - average 11,00- sf/floor
#4 - I don't remember the percentage - but I know it was less than 100 sf over the percentage to make it accessory to the B occupancy.  The building is small enough that it didn't make it a huge difference do call it an "A".


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## RLGA (Jan 18, 2021)

If you are Type IIB construction, why do you need a 1-hour roof assembly?


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## imasayer (Jan 18, 2021)

cda said:


> Well it’s about time
> 
> Welcome


Thank you!


RLGA said:


> If you are Type IIB construction, why do you need a 1-hour roof assembly?


I am rating the stair only.


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## RLGA (Jan 18, 2021)

The roof of a stairway does not need to be rated.


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## classicT (Jan 18, 2021)

imasayer said:


> Thank you!
> 
> I am rating the stair only.


But why are you rating the ceiling/roof assembly?

Shafts do not typically require enclosure at the top. See _IBC Section 713.5_, which directs you to _707.5_.

*707.5 Continuity*
_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 Sections 707.8 and 707.9.
Exceptions:

Shaft enclosures shall be permitted to terminate at a top enclosure complying with Section 713.12.
_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.


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## imasayer (Jan 18, 2021)

classicT said:


> But why are you rating the ceiling/roof assembly?
> 
> Shafts do not typically require enclosure at the top. See _IBC Section 713.5_, which directs you to _707.5_.
> 
> ...


You couldn't see it, but I smacked my forehead. I knew this.... just had the wrong thing in my head.  

Thank you for waking me up gents!


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## steveray (Jan 19, 2021)

The joint between the CMU and steel deck may need to be treated, but technically the roof structure, no...


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