In Section 220.127.116.11(3) of NFPA 13-2019 Edition, discusses that rooms or compartments 800 sqft or less (small rooms) should be calculated based on delivering 0.10 gpm/sqft over the room or the compartment by using the area of the room divided by the number of sprinklers in the room.
I believe I've overcalculated remote areas in the past.
My project now is an apartment building designed according to NFPA 13. Using residential type sprinklers with non-sprinklered combustible concealed spaces. According to Section 18.104.22.168 I need to calculate a minimum of eight sprinklers.
In the past I've calculated the eight sprinklers using the actual spacing based on the S x L rules with a 0.10 gpm/sqft density.
One room example - room dimension of 24 x 12 is 288 sqft. Two sprinklers spaced in a compartment 8'-0" off one wall and 6'-0" from adjacent wall. Using the S x L rule: 16' x 12' = 192 sqft x 0.10 gpm/sqft = 19.2 gpm each.
Or, according to Section 22.214.171.124 (3), would I divide the room size 288 sqft by 2 sprinklers, which is 144 sqft per sprinkler, regardless of the actual sprinkler distance from the walls? This second scenario would result in a 14.4 gpm required flow.
Or, was the code option (3) assuming the sprinklers are evenly centered within the compartment.
Thanks in advance for your input and clarification.
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1/14/2022 07:56:13 am
Here is a great explanation that should help you out.
1/14/2022 08:17:46 am
1/14/2022 08:55:45 am
Just wanted to add that the NFSA article Dan linked was written in 2020, so while it does say that "small room rule" does not apply to residential sprinklers per section 10.2 (2019), you still calculate it as area/# of sprinklers per 126.96.36.199 (2019).
1/14/2022 09:55:02 am
Nice...I glossed over the "residential" part of that because I don't equate small room (exceeding distance from walls) & residential sprinklers (basically EC spacing)...and the area/# of sprinklers approach typically is less than the minimum required for the sprinkler so I don't get to utilize it as much (what little residential I do anyway)
1/14/2022 12:15:17 pm
You can find a formal interp that preceded the paragraph being added. It’s been in the book for quite a while.
1/14/2022 12:54:04 pm
This is one of the most common things that I find designers don't do correctly. You basically do two calcs when using residential sprinklers in a 13 system.
1/17/2022 05:32:02 am
This! I've been questioned on several residential under 13 projects Where I show the 0.05 calc is more demanding. My experience is for the most part when the room is under 800 sqft the 0.05 calc is the most demanding. A lot of reviewers seem to miss the part where you divide the area of the room over # of sprinklers.
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