NFPA 13D Hydraulic Calculations 2 or 4-Sprinkler ?

9/7/2021

I'm reviewing a single-family home NFPA 13D system.

What is the proper way to calculate a 13D system? Is this a 2- or 4-sprinkler calculation?

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7 Comments

Alex

9/7/2021 07:28:03 am

Hi Anonymous,

NFPA 13D (2019) 10.2.1 states that “the number of sprinklers in the design area shall be all of the sprinklers within a compartment, up to a minimum of two sprinklers”.

FYI, if you fall under NFPA 13R, you are required to calc all sprinklers within a compartment up to a maximum of four sprinklers (NFPA 13R (2019) 7.1.1.3.1).

Best of luck with your design!
Alex

Alex

9/7/2021 07:29:12 am

Correction, “up to a maximum of two sprinklers”!
NFPA 13D - 2 sprinklers
NFPA 13R - 4 sprinklers

JIm

9/7/2021 08:06:56 am

NFPA 13D - .05 for 2 hydraulically most demanding.

Jesse

9/7/2021 08:16:20 am

2016 NFPA 13D 10.2.1 The number in the design area shall be all of the sprinklers within a compartment, up to a maximum of two sprinklers, that require the 0greatest hydraulic demand.

We often say 2 sprinklers in 13D designs, but it doesn't have to be. It could be just one. If you have a townhouse with smaller compartments and the designer has maxed out sprinkler spacing, you may have one sprinkler to calc.

Typically, I have my designers prove one head and two head calcs in 13D designs, though admittedly we don't do a lot of 13D stuff

Brian Cockburn

9/7/2021 09:14:43 am

As others have said, up to two sprinklers in a single compartment. If you don't have any compartments with two sprinklers and you want to be conservative; you could do two calculations with the two most remote individual sprinklers. That would give you more confidence in your design.

Good luck!

Dorgan Trostel

9/9/2021 05:09:39 pm

I like to max spacing in bedrooms where one 20x20 spacing spk will cvr the room where 2 might be needed with smaller coverage but also to get away from pesky ceiling fans.

Then just calc the larger rooms at smaller less demanding coverage with 2 spks.

caveat - sloped ceilings and sloped ceilings with beams most jurisdicitons will require either 3-4 head calc and some will boost it up to a .1 density. Every AHJ has their quirks.

GL
DT

Jay Richardson

9/14/2021 09:01:47 am

Hi DT,
It's not necessarily a quirk of the AHJ. If the compartment doesn't meet one of the 5 criteria listed in Chapter 10, then the number of design sprinklers to be calculated is required to be determined by the AHJ per chapter 10.

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NFPA 13D Hydraulic Calculations 2 or 4-Sprinkler ?

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