Use ESFR Sprinklers Under Sloped Conveyor?

12/8/2025

Do we have to use ESFR sprinklers under conveyors, which have slope, solely because the roof system is ESFR?

What code basis—if any—would actually require ESFR protection under conveyors in this situation?

I am currently designing a sprinkler system renovation on a package sorting facility that we did the original conveyor design on 4 years ago. The existing 500,000 sqft open warehouse had (13) k-22 ESFR systems that we did not design. I designed all the systems for the catwalks, mezzanines, and under conveyors using Standard 5.6k quick response, standard spray sprinklers (Reliable RA1425) with shielding under open grate flooring.

The new systems all have their own risers coming off the existing 10" manifolds. It was all hydraulically calculated and approved by the city.

Now we are designing / renovating the conveyor systems because the client added, removed & moved a bunch of conveyors. I removed all sprinklers and pipe from the areas being changed, and most of the new or changed areas we able to reuse existing outlets that we had demolished pipe from. We used the same pipe sizing scheme, same type of sprinklers, and redid all hydraulic calculations.

BUT now the plan reviewer is rejecting the plans citing:

THE SPRINKLER PROTECTING THE BUILDING ARE CLASSIFIED AS ESFR, THE SPRINKLER PROTECTING THE AREA UNDER THE CONVEYORS SHALL BE OF THE SAME TYPE AS PER NFPA 13, 2019, SECTION 9.5.5.3.3.

I responded with NFPA 13 20.6.2, ESFR are only approved to a slope of 2:12 and most of the conveyors are way past that; and noted again that that the existing system is 5.6k.

To which he responded:

THE SPRINKLER PROTECTING THE BUILDING ARE CLASSIFIED AS ESFR, THE SPRINKLER PROTECTING THE AREA UNDER THE CONVEYORS SHALL BE OF THE SAME TYPE AS PER NFPA 13, 2019, SECTION 9.5.5.3.3 WE DO NOT UNDERSTAND THE RESPONSE TO THIS COMMENT, SECTION 20.6.2, WHICH ADDRESSED THE SLOPE OF THE ROOF NOT THE PROTECTION UNDER THE CONVEYOR. INDICATE WHICH STANDARD ADDRESSES THE HYDRAULIC CALCULATION FOR PROTECTION UNDER A CONVEYOR, WE CAN’T FIND THE SPECIFIC DESIGN CRITERIA FOR PROTECTION UNDER THE CONVEYOR USING ESFR SPRINKLERS. UNLESS THE SAME CRITERIA US FOR THE ROOF SYSTEM WILL APPLY UNDER THE CONVEYOR.

Has anyone ever run into this?

If have to use k-22 ESFR, it would be disastrous to the calcs, not to mention the existing system I am coming off of. Thanks in advance.

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12 Comments

Brett

12/8/2025 06:57:25 am

Your previous designs should have used ESFR sprinklers under those conveyors because there was no other option in previous editions of NFPA 13, but the 2025 edition of NFPA 13 has other options.

Read section 14.2.10.3.7 of the 2025 edition of NFPA 13. If there is no high piled storage under the conveyors then you can use quick response sprinklers and design the system to protect only the area under the conveyors.

Joe Bergstrom link

12/8/2025 08:46:20 am

There is no storage at all under the conveyors, catwalks or mezzanines. I have done MANY other package sorting facilities like this for different Corporations, in different states & cities, some were FM and some were just NFPA 13. I have never run into any AHJ wanting ESFR heads under the catwalks or conveyors. They are normally treated as a separate system like a mezzanine would be, they have their own riser off of the manifold and all.

Jack G

12/8/2025 01:08:31 pm

I believe the separate calculations is because the roof ESFR s water is obstructed by the conveyors so a new calculation is required using the area under the conveyors as a new ceiling.

12/8/2025 08:52:10 am

Well, I learned something today. I would have thought, with the number of conveyors I have seen with standard spray sprinklers underneath them, that surely this plan reviewer was wrong. But it appears as though Brett guidance is correct. Seems the best bet is to attempt to cite 2025 edition which has specific language for conveyors.

Dan Wilder

12/8/2025 08:58:25 am

Agree with Brett and it is unfortunate that the previous design did not get flagged (not sure what the previous NFPA standard was) Having completed several DC's and this issue comes up a lot, we have provided ESFR beneath conveyors, including sloped installations, that match the overhead for sprinkler type, K-Factor, and pipe sizing and have had very little issue with inspections and Insurance sign offs. We have been able to use the lesser available storage height to use a less demanding ESFR sprinkler beneath larger catwalks and platforms.

Chad

12/8/2025 08:59:39 am

Yeah he is right. The slope under the conveyer is irrelevant when providing coverage under obstructions with ESFR when applying pre-2025 NFPA 13.

Gotta be ESFR below as well.

12/8/2025 10:59:19 am

This is going to get interesting and will present a whole world of problems because of the existing heads being standard 5.6k spray heads. Thankfully the FP Installer used another design firm for the original conveyor layout so we're not reliable for it, but technically we should be replacing all the existing heads with ESFR or else we will have 1/2 a 5.6k standard and 1/2 k22 esfr. I guess we always got away with it because we would connect to the mezzanine systems which were standard heads because there is no storage below them. this particular building was built as a shell type warehouse with 42' ceilings, so I guess they used k22 esfr just to allow for almost any tenant to use the space.

12/8/2025 11:07:27 am

Thank you all for your insight into this, I greatly appreciate it. Hopefully this will not be much of a huge deal for us, although I suspect it will be for my client.

12/8/2025 01:03:05 pm

From what I recall the sprinklers under the conveyor are a separate calculation and treated as a new ceiling ( you do not need to add to the roof demand or calculate with roof sprinklers)

12/8/2025 01:50:48 pm

That was my thought as well, however there isn't anything in NFPA 13 prior to 2025 that supports that. They are still run as a separate system, and calculated as one.

Anthony

12/8/2025 02:14:29 pm

This is a rough one, obstruction coverage needs to match the system above typically.

I could see an argument where the floor space covered is actually OH2 and considered manufacturing or finished goods processing and an F-1 or F-2. In those cases where ESFR is protecting a lower hazard I could see the sprinkler change acceptable.

12/29/2025 04:35:17 pm

Just to clarify, the allowance to use standard spray sprinklers underneath conveyors was introduced in the 2022 edition of NFPA 13, when the whole conveyor section was added to chapter 14. Section 14.2.11.4 option (1) "Quick-response standard spray sprinklers shall be permitted to be installed below conveyors without high-piled storage located underneath". This is also the section that allows you to omit protection underneath conveyors up to 4'-0 wide.

Use ESFR Sprinklers Under Sloped Conveyor?

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