Use Small Room Rule with Mixed Ceiling Height?

11/5/2021

Can I use the small room rule out of NFPA 13 in an office with varying ceiling heights?

The room has a partial 8'-0" ceiling and a partial 8'-6" ceiling with the vertical section closed in. We're under NFPA 13-2016. The sprinklers meet the obstruction rules out of Chapter 8 and the spray pattern develops to protect the entire floor space without being obstructed by the change in ceiling elevation.

Based on the definitions below, it looks like the ceiling doesn't need to be flat, but I want to make sure I'm applying the rule correctly and I can use a 9'-0" dimension for the small room rule in this situation.

NFPA 13-2016 Section A3.3.2.2 defines a small room rule as a compartment of light hazard occupancy classification having unobstructed construction and a floor area not exceeding 800 sqft.

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8 Comments

Pete H

11/5/2021 06:54:20 am

Long as you don't have an unprotected ceiling pocket as allowed by 8.6.7 and 8.8.7 exceeding 32 square feet and there's no unprotected area above a cloud ceiling (doesn't sound like you have a cloud ceiling anyway), sounds good (in my opinion).

Pete H

11/5/2021 06:55:24 am

Er, ignore this comment, this is the extra rules for design area reduction.

Yeah, sounds fine on the small room.

Alex

11/5/2021 07:08:18 am

Hi,

From my interpretation of the code, if you have complete floor coverage, you are permitted to use the small room rule.

Thanks,
Alex

Glenn Berger

11/5/2021 08:26:32 am

You are correct in your interpretation of the small room rule.

SCHULMAN

11/5/2021 08:39:53 am

JUST LEARNING THIS STUFF,
So I would appreciate if someone could verify that the reason this works is NFPA 13 (2016) 8.6.4.1.1.3 (B) in conjunction with the Small Room rules ?
Or am I interpreting wrong .. ?

thanks

Franck

11/5/2021 10:45:43 am

8.6.4.1.1.3 regulates how you will install sprinklers when you have some possible obstructions to the sprinkler pattern discharge (that would prevent a correct wetting of all areas located on the ground floor).
This does not affect the method you chose to calculate your system (except by the fact you may have different area coverage per sprinkler).
This means that you may space your sprinklers differently in the room, depending on the elevation between the 2 ceilings.
But at the end, if the number of sprinklers and area covered by your room satisfy the small room rule, there is no reason not to apply it.

11/5/2021 08:57:33 am

This is an acceptable means of protection and the small room rule for sprinkler layout does apply in this situation.

Jesse

11/5/2021 11:31:23 am

Yep, small room rule can apply here

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Use Small Room Rule with Mixed Ceiling Height?

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