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Architecture/Ceiling assembly


QUESTION: I am designing a church and I need to find  1 hr rated ceiling assembly for a one hour rated corridor, the walls are metal framing ( U.L design 465). The building is a pre engineered metal frame. I checked the ul Fire book but I don't know which one to use.

ANSWER: Carlos,

Although I am uncertain what your type of construction is (Type IIB), you will likely have resilient channels at 24 inches on center and a minimum of one layer of 5/8" fire-rated drywall.

Download this manual and look at page 50 for various roof-ceiling treatments:

But if your ceiling is attached to the bottom side of either first or second floor, then you will need to look at earlier pages of that same manual for a floor-ceiling assembly that would be consistent with the type of floor joists you are using.

I am assuming here that your fire inspector is telling you that this ceiling needs to be fire rated rather than making your own assumption.  Is this building non-sprinkled with a fire area greater than 5,000 S.F. and/or the number of seats greater than 300?  I had several questions back in December for you that would give me a better picture of what you are dealing with.

Again I say, "good luck!"

Richard Burton, AIA
Registered Architect
ICC Certified Plan Reviewer
NFPA Certified Fire Plan Examiner

---------- FOLLOW-UP ----------

QUESTION: Hi Richard,
Yes, this is the same pre engineered metal rigid frame building (10,000 s.f, type II-B), where 5,000 s.f. belong to the church and the other half is a mercantile occupancy and there is a 2 hr tenant separation between them.
I spoke with the fire inspector and we agreed that if I demonstrate that the occupancy in the church (assembly A-3) is less than 300 people I wont need sprinklers, but I need to provide 1 hr fire rated corridor. So that is the reason why I needed the ceiling assembly. Building height is around 15 ft. but the ceiling in the corridor will be only 8 ft. I think I could use either P524 or P525. What do you think?
Speaking about occupancy, I am doing the calculation room by room applying the occupancy factors, but do I need to consider bathrooms and hallways areas in my calculation? if that so, what is the occupancy factor for these areas. The church has offices, classrooms, kid's rooms and a sanctuary.

Thanks for your help Richard.

ANSWER: If given the choice between P524 and P525, I will always choose what the drywallers choose which is resilient channels at 24" on center and then one layer 5/8" fire-rated gypsum board.  That would be more like P525 which is a 2 hour fire rated ceiling.  But did you say that you only need a one hour fire rated ceiling?  Be careful not to call out a UL number that is overkill.

---------- FOLLOW-UP ----------

QUESTION: All the details describe steel trusses, but non of them describe metal frame with roof purlins, that is what I have. Should I find a detail that matches what I have or can I use the P526 for example?



RC-1 channels or equivalent attached to metal frame and/or roof purlins spaced no greater than 48" on center.
Spacing of resilient channels will be 16" on center.
Attach 5/8" Sheetrock Firecode C Core gypsum to resilient channels.
Finish joints.
Insulation above concealed ceiling space and over gypsum ceiling membrane is optional.
One-hour fire-rated ceiling assembly EQUIVALENT to UL Design P526

The key word above is "EQUIVALENT".

Most seasoned code officials will recognize that not every possible combination of building materials and protective coverings has been tested but a slightly different combination of materials should perform the same - as if the drywall was protecting a roof truss covered with a plywood deck.  That is why my first answer suggested that you will likely have resilient channels at 24 inches on center and a minimum of one layer of 5/8" fire-rated drywall.  But if your code official insists that you call out a UL Design number and show a detail that is exactly like that UL Design number, then that is exactly what you need to do.  If that is the type of fire inspector you are dealing with and your type of roof system has never been tested and approved with any protection, then I would recommend that you design/build a floor-ceiling assembly below the roof consisting of 9-3/8" deep 16 gauge steel joists 24" o.c., and apply two layers of drywall to the bottom of these new ceiling joists using the same resilient channels.  See UL Design L527 on page 32 of the USG Fire Resistant Assemblies.

And please don't forget to rate my answers here on AllExperts.  I am currently ranked fourth out of seven architects and, not long ago, I was at the top.

Thank you,

Richard Burton, AIA
Registered Architect
(but not licensed in Florida)
ICC Certified Plan Reviewer
NFPA Certified Fire Plan Examiner


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Richard Burton AIA


A combined total of 25 years experience with construction, architecture, and building code enforcement. Ask me about residential and commercial design. Ask me about design aesthetics, structural methods, and building something that will withstand severe weather conditions. Ask me my opinion about YOUR design ideas and I will tell you the merits of good design and challenge your thinking about practical issues. Ask me how to best find and work with your local architect and approach general contractors to get the most value for the least amount of headaches. You can ask me about improving your energy efficiency and things that are both green and practical. But don't ask me about solar panels and wind turbines unless you are currently paying your utility company 35 cents per Kilowatt. Otherwise the math does not justify the initial cost and return on investment. Ask me any building code question and how to get a building permit from the most difficult enforcement agencies.


Here in the midwest, we design and build "green" in ways that make sense. My construction methods prioritize weather resistance, ease of maintenance and durability. While a graduate student in San Diego, I taught drafting and history of architecture. After working ten years for other architecture firms, I have started my firm Arrow Architecture in 2008. More than half of my work involves commercial office buildings. But my portfolio of work also includes custom homes, residential additions, home remodels, and second story additions.

President-Elect of American Institute of Architects - Lincoln, NE

B.S. Architecture - (Interior Design) University of Nebraska Lincoln 1997 Master of Architecture - (Urban Design and Professional Practice) NewSchool of Architecture - San Diego 2004 Graduated Summa Cum Laude ICC Certified Building Plans Examiner

Awards and Honors
AIA Henry Adams Medal and Certificate

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