Use Area Increase for NFPA 13 + 13R Building?

6/1/2021

I have inherited a totally fun project, a R-2 III-B multifamily residential building at 27,300 sqft per story, three stories total. I'm on the architect side.

Our mechanical engineer did a 61G (Florida fire suppression analysis) and designed the central lobby to be under NFPA 13 and the rest of the building NFPA 13R. I immediately thought where are the area separation firewalls, because we are over our allowable area for a III-B. The building is in construction, trusses have been set.

I was told that you can do an area increase in the hydraulic calculations, one with the NFPA 13 portion of the building and one with NFPA 13R add them together and get your increase. I'm calling BS because I cannot find this in the code anywhere, but supposedly this is coming from a FP consultant.

Any clues on the location of this allowance in code?

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7 Comments

Jeff Hugo

6/1/2021 08:17:06 am

The building code does not give a building area increase for NFPA 13R or partial NPFA 13 systems. The code does not address hydraulic increases or decreases for building area.

The sprinkler design area of the NFPA 13 system can be reduced, lowering the water demand, when using quick response sprinklers.

Paul Pinigis link

6/1/2021 08:42:59 am

If the applicable code is based upon the IBC (2015 or later), table 506.2 does differentiate between building that sprinklered in accordance with Section 903.3.1.1 (NFPA 13) and Section 903.3.1.2 (NFPA 13R). But, the allowable area for R-2 building of Type III-B construction is the same for not-sprinklered and for NFPA 13R at 16,000 SF.

Jonathan Sullivan

6/1/2021 09:03:17 am

I can't speak to the interaction between NFPA 13 and 13R, others here are better suited to discuss.

At first glance under 2020 FL building code for R-2 Type IIB, your allowable area factors are 48,000 sf of Type IIB R-2 when fully sprinklered using a NFPA 13 system and 16,000 sf when using a NFPA 13R system.

You'll have to review table 506.2, its footnotes, and section 903.1.1 with your FP consultant to make sure you are using the proper installation standard for your given area factor then take the appropriate 506.2 equation to figure your allowable building and floor area.

sean

6/1/2021 12:23:16 pm

area increase requires the system type to be throughout the building

Casey Milhorn

6/1/2021 12:36:57 pm

The difference from 13R to 13 isn't a huge deal a lot of times. The biggest gotcha will be the possible need for interstitial heads in combustible concealed spaces. That will be the largest cost impact. The sprinkler demand when using residential sprinklers is going to be very similar whether it's 13 or 13R (if not identical). Areas outside the units still are protected per 13 anyway and as stated can be a reduced area when QR sprinklers are used. Other gotchas might be some differences in balcony protection depending on the edition of 13 or 13R that is applicable. Long story short, if a full 13 system is required throughout it might not be a huge deal other than the interstitial heads.

6/1/2021 08:34:56 pm

i would agree not a huge deal, but it is still significant.
Attic protection, density starting at .1 instead of .05, closet protection, etc.

people do not like the change order

Alex Abossein link

6/1/2021 08:36:21 pm

See:
https://www.meyerfire.com/blog/summary-of-differences-in-nfpa-13-13r-13d

Use Area Increase for NFPA 13 + 13R Building?

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