Wet Sprinkler Zone Next to Pre-Action Zone?

7/31/2026

In an open, fully sprinklered building, can 50% of the floor area be protected by an automatic wet system, while the remaining 50% is protected by a pre-action system?

There is no wall separating the two areas. Thanks in advance.

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7 Comments

Pete H

7/31/2026 06:02:44 am

As long as the 50% that is wet is heated/conditioned to have wet pipe and both systems are installed correctly with neither exceeding the area limitations for their hazard and type of system: yes, that's still a fully sprinklered building.

If 50% of a refrigerated storage facility was the refrigerated parts, that'd have a dry or preaction system.

Assuming the pipe is only going through heated/conditioned spaces and following all other requirements for a wet system for all the other parts, no reason that shouldn't be a wet system.

anthony

7/31/2026 07:41:59 am

With no context, yes this is acceptable. Nothing I can recall from the code that would prohibit this.

Steve Gaillard

7/31/2026 08:10:34 am

Are the hazards the same? but either way yes. There is no standard in NFPA preventing 2 different system types in the same area. If they are different hazard classes you need to either have baffles, walls or extend the higher hazard to 15' around the higher hazard.

Glenn Berger

7/31/2026 08:25:30 am

There are no requirements to separate areas with differing types of sprinkler systems.

I am assuming that the preaction system is protecting some "critical" process areas and the wet-pipe systems is protecting standard hazards.

It will be questioned by everyone who inspects the systems.

Jonathan W.

7/31/2026 09:26:11 am

I do not necessarily agree with the other commentors on this one. We should be careful as to not get trapped in the "well the code says it's ok" mindset.

While the code may not specifically prohibit this design arrangement, logically speaking, this could create the same situation as putting quick-response sprinklers in the same compartment as standard-response sprinklers.

Refer to NFPA 9.4.3.2. The skipping of sprinklers can occur and lead to an unnecessary number of sprinklers activating.

If I were the DOR, I would not recommend this design arrangement. I also agree, this will be questioned by every AHJ for the lifetime of the system.

Chad

7/31/2026 10:36:07 am

Yes but... the preaction detection needs to be coordinated and reviewed to ensure that a baffle/draft curtains arrangement is not required.

I agree the EOR needs to look closely at the overall design and ensure we aren't missing something.

Dave

7/31/2026 11:53:04 am

Assuming a single interlock system with properly designed detection, and similar required densities on both sides, I don't see an issue. The concern being a fire at the border of the two. While air is pushed out on the pre-a side, there could be some delay putting water on the fire, but maybe this is offset by the earlier notification to owner and FD provided by the detection. Also helping in that border fire is the higher density since the water is being delivered to the fire area via two systems, each of which were designed for the full area.

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Wet Sprinkler Zone Next to Pre-Action Zone?

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