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Individual-head (i.e. not deluge) sprinkler systems come in three flavors:

  • Wet-pipe systems have water pressure at the head at all times -- they are the quickest to respond, but can't be subject to freezing conditions and are too risky for water-sensitive spaces
  • Dry-pipe systems have compressed air in the pipe between the head and the dry-pipe valve -- when the head fuses, the dry-pipe valve is opened by the pressure change and delivers water to the system. This can be used when a freeze risk exists, but is slower to respond.
  • Preaction systems are used to provide external confirmation (from say an alarm system) before the sprinklers activate -- the alarm system must open the preaction valve before water can flow onto the fire. This is used when accidental discharges must be controlled at all costs.

This raises the question: under NFPA 13/13R/13D, can individual fire zones be protected by a dry-pipe or preaction system while the remainder of the building has wet-pipe sprinkler protection? For instance, the attic, garage, and unfinished basement in a home could be dry-pipe protected to avoid freeze-ups while the finished spaces are protected by a conventional wet-pipe system.

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  • $\begingroup$ In my experience, this depends on what you can negotiate with the insurance company. After all, the purpose of a fire protection system is management of risk. $\endgroup$ – morristtu Feb 25 '16 at 3:32
  • $\begingroup$ @morristtu -- I suspect most homeowners' policies aren't negotiable at that level (one of the prime applications for this I see is in single-family dwellings that are being fitted with NFPA 13D systems)...or are they? $\endgroup$ – ThreePhaseEel Feb 25 '16 at 3:55
  • $\begingroup$ As this is a risk based decision, I don't think Engineering StackExchange can provide a proper answer. The NFPA states, "A home fire sprinkler system can reduce the homeowner’s insurance premium." This is best left between the homeowner and the insurance provider. Btw, that's an awesome screen name. $\endgroup$ – morristtu Feb 25 '16 at 4:07
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    $\begingroup$ @morristtu, I believe this is still an engineering question, because technical specifics are being offered, irrespective what the future outcome may be with an insurance company. Furthermore, if you want to argue that this is a risk-based question, then surely risk assessment and mitigation are an engineering function? $\endgroup$ – My Other Head Feb 25 '16 at 8:28
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Yes, this is permissible

NFPA 13 7.1.3 explicitly permits this:

7.1.3 Auxiliary Systems. A wet pipe system shall be permitted to supply an auxiliary dry pipe, preaction, or deluge system, provided the water supply is adequate.

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  • $\begingroup$ It seems as though you could expand upon this. Given that you're self-answering 2.5 years later, surely there was some investigation that you performed and would be relevant to the answer. $\endgroup$ – user16 Oct 1 '18 at 2:15
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    $\begingroup$ @GlenH7 -- what happened is that I found a newer copy of NFPA 13 and was reading it when I found this clause. :) (Unfortunately, there's neither an Appendix A rationale nor a definition for "auxiliary system" in the Code, though...) $\endgroup$ – ThreePhaseEel Oct 1 '18 at 2:18
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From a risk management standpoint, dry pipe or preaction systems should only be used when antifreeze wont work (E.g. too cold) and when heat tracing is unreliable or impractical (E.g. power outages).

5.4.2* Piping in areas that cannot be maintained reliably above 40°F (4°C) shall be protected by use of one of the following methods: (1)*Antifreeze system using a listed antifreeze solution in accordance with NFPA 13 (2) Dry pipe system (3) Preaction system (4) Listed dry pendent, dry upright, or dry sidewall sprinklers extended from pipe in heated areas (5) Heat tracing in accordance with 6.7.2.2

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