Sprinkler Quantity for Residential Corridor Calc?

4/13/2022

I am working on a mixed-occupancy project using NFPA 13 (2013 Edition). The ground floor is commercial space and Levels 2-6 are residential.

The residential areas use residential-type sprinklers with two hydraulic calculations; one in a suite on Level 6 (4 sprinklers), and the other in the Level 6 Corridor.

How many sprinklers should be included in the corridor calculation?

Section 11.2.3.4.2 suggests it should be 7 sprinklers since they form a line down the corridor.

Section 11.3.1.1 suggests that it should only be 4 sprinklers since they are residential-type.

What section is correct here?

Thanks in advance.

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11 Comments

Peter Howard

4/13/2022 06:37:06 am

I'd go with four because they're residential type sprinklers and you're in a residential occupancy, just a common corridor.

But I am curious to see if anyone would go with the 7 sprinklers.

Anthony

4/13/2022 08:14:54 am

7 if you're using QR sprinklers.
4 if you're using residential heads.

The type of sprinkler matters, as always.

RayJ

4/13/2022 08:20:35 am

I would calc both and have done a building similar to this.

4/13/2022 08:26:39 am

I'd be more inclined to go with 11.2.3.3.6 for most corridors assuming the corridor allows the room design method is allowed to be used (which is 5 sprinklers, residential sprinklers while spaced like extended coverage sprinklers, are not extended coverage sprinklers and do not fall under the 75 linear feet rule). I don't think you can use 11.3.1.1 for corridors since it is not a dwelling units as per 11.3.1.5. Curious to see if others use the 4 head calculation in the corridors since you are allowed to use residential heads as per 8.4.5.1.

James Phifer

4/13/2022 08:27:33 am

The appendix (2016 ed) figure A.11.3.1.1(a) detail (b) shows an example of a calculated area in the corrido with 4 residential sprinkler heads.

Casey Milhorn

4/13/2022 08:30:30 am

Four, if the corridor is connected to at least one residential unit. If you have common areas, unconnected corridors, etc... then you will use SSP QR sprinklers and calc accordingly. I don't always do a corridor calc when using residential heads because many times your corridor heads are fed from a larger main down the middle (1-1/4" to 2") and your units are fed with 1". It would be a rare exception to need the corridor calc (for example, unit heads are spaced at 14x14, and corridor heads are at 20x20. Or if using a different K factor for units than for corridors). Even if you factor in a little more delta flow at the corridor heads, its not near enough to outweigh the friction loss through the 1" in the units.

Great question....

EYount

4/13/2022 08:30:47 am

If it’s residential sprinklers it would be 4 and if it’s QR it would be 5.
11.2.3.3.7 Where the area under consideration is a corridor protected by a single row of sprinklers with unprotected openings, in a light hazard occupancy, the design area shall include all sprinklers in the corridor to a maximum of five, or when extended coverage sprinklers are installed, all sprinklers within 75 linear feet (22.9 linear meters) of the corridor.

Scott Stoltenberg Jr

4/13/2022 08:37:35 am

I would have to say it is 5 based on 11.2.3.3.6 or 11.2.3.3.7.

I just had this similar situation myself where I had residential heads under NFPA 13.

Since this area is Light Hazard and not residential, you will have to calc it with the "greater" (worst) of the two. Density, Head spacing with a min. pressure of 7 psi or per the pressure and the flow in the sprinklers listing.

• NFPA 13 19.4.1.3 states: “Unless the requirements of 19.4.1.4 are met, the minimum required discharge from each design area sprinkler shall be greater of the following:
1) In accordance with minimum flow rates indicated in sprinkler listings
2) In rooms or compartments 800ft² (74m²), calculated based on delivering a minimum of 0.1 gpm/ft² (4.1 mm/min) over the design area in accordance with the provisions of 9.5.2.1
3) In rooms or compartments 800ft² (74 m²) or less calculated based on delivering a minimum of 0.1 gpm/ft² (4.1mm/min) over the room or the compartment using the area of the room divided by the number of sprinklers.
Residential heads are typically calculated with a density of .05 but the calculation is driven by minimum flow rates in their listings, which in this instance is the greater of the options 1) & 3) because 2) does not apply because they are <800ft². I have provided additional calculations under the light hazard or item 3) from above to show that the original calculations, in fact, where the greater of the two options.

While I know this is 2019 you can find the similar reference in the 2013 edition at 11.3.1.3.

This was also my response when the plan reviewer was confused because were using residential heads in a light hazard area, since they can be point in adjoining corridors.

Hopefully this helps :D

Jack G

4/13/2022 08:48:48 am

I personally, because residential systems have unprotected areas/ rooms, would use the 7 sprinkler design.
I also try to align sprinklers near doorways, in case one is propped open.
A pipe size difference in a corridor has minimal effect on the cost.

Alex

4/13/2022 10:29:31 am

Hi Jack, curious on your design approach here. Would you add additional heads if the doors don't align with your spacing? Seems like it could increase the number of heads real quick!

Todd E Wyatt

4/13/2022 10:34:46 am

I recommend you have the Architect-of-Record (or AHJ) verify the exact "residential" occupancy(s) per the applicable IBC ...

Group R-1 (Hotels)
Group R-2 (Apartments)
Group R-3 (Dormitories)
Group R-4 (Board & Care)

... since each Group R# has different Fire Protection requirements per IBC Chapter 9.

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Sprinkler Quantity for Residential Corridor Calc?

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