Is Multi-Level Ceiling Sprinkler Spacing Correct?

5/18/2023

We have an NFPA 13 system, using residential sprinklers, in a dwelling unit that has 2-levels of smooth flat ceilings. There are two levels of ceilings (9'-0" on left, 8'-0" height on right).

Image provided below:

Sprinklers are hydraulically calculated at their listing with a 20 x 20 spacing, and there is not an issue providing 0.10 gpm/sqft.

See the spacing above - is this an allowable arrangement though considering how it was calculated?

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11 Comments

Pete H

5/18/2023 06:51:29 am

It looks ugly, but it's fine.

The head within 10'-0" of the ceiling divide is on the lower ceiling, so it will spray further and cover the floor area of the higher ceiling where the head is over 10'-0" from the ceiling divide.

Ideally, I'd move the head that is 13'-0" away from the ceiling divide to 7'-6" away because then I know it'll spray underneath the 12" difference in ceiling (Table 8.10.6.1.2 in NFPA 13 2016) and it looks like it'll still be well within 10'-0" of the wall, but that's just making it look nicer rather than sheer compliance.

In terms of sheer code/listing compliance, this arrangement works. Most I could see causing an issue is if the ceiling the pendants/uprights are protecting underneath a combustible ceiling with no further overhead protection. Then because of the combustibility of the construction, I could see an AHJ wishing to go beyond the listing and want the head to be within 10'-0" of the divide so it's at least wetting the combustible construction members.

Pete H

5/18/2023 09:00:41 am

I'm wrong, Anthony's right. Unless listed otherwise, residential heads are to be within 1" to 4" deflector to ceiling.

So ultimately, move the head 13'-0" away from the ceiling divide to be within 10'-0" of the ceiling divide.

If you want to be awesome, keep it over 7 ft off the ceiling divide but under 10'-0" so there's zero doubt the sprinkler sprays underneath.

Anthony

5/18/2023 07:01:16 am

This is not an appropriate lay out of sprinklers unless the sprinklers are allowed to be 12'' down from ceiling. In many cases pendant res sprinklers are only allowed to be 8'' maximum down from ceiling per their listing. Thus the area 3' left from the edge of the step in ceiling height is in an unprotected area.

There is no such rule similar to 8.6.4.1.1.3(b) (NFPA 13-16) for residential sprinklers.

There is an argument to be made about ceiling pockets and the whole area under the sprinkler being protected. However, I do not believe the arrangement shown indicates a "pocket."

Dave Sornsin

5/18/2023 11:25:40 am

I agree with Anthony (and Pete's revised comment): Residential sprinklers don't have an equivalent to 8.6.4.1.1.3(b) (NFPA 13-16). I'm guessing this is because of the high wall wetting requirement for residential sprinklers.

What's interesting, is that in later editions (see NFPA 13-19 12.1.8.1.2), with limitations including a 600 sq.ft. compartment, the committee allows installation of residential sprinklers in or next to beams up to 14" deep which could delay the operation AND not achieve the high wall wetting. So if operating in the 2019 or later edition could you consider the entire ceiling to the right of the dashed line a really wide beam? LOL.

SCHULMAN

5/18/2023 08:13:46 am

i would add another sprinkler 2' left of the center line. your chandelier or ceiling fan at the high ceiling won't be a problem and you solve the question of coverage... and it will look nicer.... I'm assuming you will be installing concealed flush and not dropped sprinklers... please. ...

R Jackson link

5/18/2023 08:36:34 am

Just because you can design something per code doesn't mean it will have the best appearance. I would center both heads, as long as this would meet code. If not, then 2 heads.

Franck

5/18/2023 11:01:14 am

As indicated above, the possible issue is that a fire originating under the 9 ft ceiling, but at the edge with the 8 ft ceiling will first only operate the sprinkler under the 9 ft ceiling, with 3 ft not correctly covered… until the sprinkler under the 8 ft operates.
Being allowed to go up to 20 ft spacing does not mean you have to have these 20 ft.
For a better coverage and efficiency, I would space both sprinklers by 15 ft, starting 7 ft 6 in from each wall (centered in each “pocket”).
Much nicer to see and more efficient (reliability).
And this won’t really impact your hydr. Calculation to reach 0.1 gpm/ sq ft in this area.

Franck

5/18/2023 11:06:07 am

Note that this would have been a lesser reliability issue if the sorinkler located 13 ft from the edge would have been the one under the 8 ft ceiling.
A fire originating close to the edge between both ceiling, but under the 8 ft ceiling area, between 10 ft and 13 ft from the sprinkler, would activate more quickly the sprinklers on both sides as the heat tends to collect to the highest point : heat plume under the 8 ft ceiling would reach the sprinkler located under the 8 ft ceiling, but on the other side, the heat plume will quickly reach the 9 ft ceiling level and activate the second sprinkler…

Naj link

5/18/2023 11:46:58 am

Vertical change in ceiling elevation less than 36 in. sprinkler positions are fine.
In this case sprinklers can be designed as ceiling was flat.

danefre

5/19/2023 07:21:30 am

That section is for standard spray sprinklers only and doesn't apply here. See comments above.

Naj

5/23/2023 08:04:23 am

Yes, that's for standard sprinklers but reference to NFPA 13-2019 section 12.1.10.1.2 (1) sprinklers shall be in accordance with 9.5.5.2, table 12.1.10.1.2 and figure 12.1.10.1.2 (a)

9.5.5.2 Sprinklers shall be positioned in accordance with the minimum distances and special requirements of Section 10.2 through section 14.2 so that they are located sufficiently away from obstructions such as truss webs and chords, pipes, columns, and fixtures.
As per section 10.2 ; Figure 10.2.6.1.1.3 (A) vertical change in ceiling elevation greater than 36 in then maximum distance to change in obstruction is ½ S.

so it should apply

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Is Multi-Level Ceiling Sprinkler Spacing Correct?

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