Can central alarm smoke detectors be used instead of 120v smoke detectors in a new residence?

Question

Code requires that new residential construction have a smoke alarm in each bedroom and outside of each bedroom, and that the smoke alarms be interconnected. (They all go off at once).

If you plan to install a central alarm system, (the type that combines burglar and fire alarm with a central control panel that is remotely monitored), and you place a siren in each room, would this meet the code requirements?

Or do low voltage alarms always have to be installed in addition to (not instead of) the interconnected 120v alarms?

IRC 2012/NEC 2014

Answer 1

In a single family dwelling, it would be best to use regular smoke alarms. Pick a brand that also sells an interconnect relay, and you can use that to connect it to your security system.

To answer your question, yes you should be able to use low voltage smoke detectors as long as the central control panel has a battery backup and the overall system functions similarly to a normal system. If the smoke detectors don't have a built-in audible notification device, then you'll also need to install one of those in each required location.

Drawing up a building plan to show the Fire Marshal your proposed fire & life safety plans will be an important step. Getting that plan approved will help make sure you don't purchase and install a bunch of equipment that doesn't pass their interpretation of the code.

Usually you would only go through this much extra work if you wanted addressable smoke detectors, but in a single family dwelling that's an extra expense that's not needed in my opinion. That level of system is usually only needed in a commercial or multi-family setting.

In a commercial or multi-family setting, you'll usually want strobes and horns in public areas, horns in each unit, pull stations in the hallways, and the central monitoring station to be able to tell the first responders exactly which zone or location triggered the alarm. In a a single family dwelling, you should be able to easily locate what area needs attention without those features. Regular smoke alarms typically have latching alarm indicators, so it helps you diagnose problems by letting you know which device triggered the alarm.

R314.2 Smoke detection systems.

Household fire alarm systems installed in accordance with NFPA 72 that include smoke alarms, or a combination of smoke detector and audible notification device installed as required by this section for smoke alarms, shall be permitted. The household fire alarm system shall provide the same level of smoke detection and alarm as required by this section for smoke alarms. Where a household fire warning system is installed using a combination of smoke detector and audible notification device(s), it shall become a permanent fixture of the occupancy and owned by the homeowner. The system shall be monitored by an approved supervising station and be maintained in accordance with NFPA 72.

R314.4 Power source.

Smoke alarms shall receive their primary power from the building wiring when such wiring is served from a commercial source, and when primary power is interrupted, shall receive power from a battery. Wiring shall be permanent and without a disconnecting switch other than those required for overcurrent protection.

Answer 2

The two requirements are different. Some codes may allow overlap or substitution in some circumstances. Others not so much.

From a pure reliability standpoint, a "system" is inherently less reliable than numerous autonomous smoke alarms because a "system" relies on many single points of failure (motherboard, power supply, alarm relay, etc). A distributed smoke alarm requirement is much less likely to fail entirely, in multiple diverse points, all at the same moment, when it matters most. Having both would be good.

If the code requirement is "smoke alarm" in each bedroom, then that's what you're required to install, unless you can point to a specific exemption in the applicable code. Whether there may also be a "fire alarm system" permitted in the code does not necessarily remove the single-station smoke alarm or multiple-station smoke alarm requirements. In other words, they may supplement each other, but the specific requirement quoted in IRC 314 is for "smoke alarms" not just a "fire alarm system".

For comparison, NFPA 1 (2009) National Fire Code specifically states

13.7.1.4.9.1.4 System smoke detectors in accordance with NFPA 72 and arranged to function in the same manner as single-station or multiple-station smoke alarms shall be permitted in lieu of smoke alarms.

... quoting NFPA 101: 9.6.2.10.1.4

Identical wording is in NFPA 1(2015) 13.7.1.8.6, for those jurisdictions that have adopted the later version, quoting NFPA 101(2015): 9.6.2.10.6.

While we're there, NFPA 101(2015) clearly prohibits substitution of smoke alarms going "the other way":

9.6.2.10.2 Where automatic smoke detection is required by Chapters 11 through 43, smoke alarms shall not be used as a substitute.

If fire code (or life safety code) conflicts with requirements that are more strict than similar provisions in the building code, then you would generally be required to follow the more strict provisions, absent an official variance.

Also worth noting that battery-backup requirements for "fire alarm systems" may be quite different from those of "smoke alarms".

Bottom line, building code, fire code, life safety code, alarm code, and pertinent enacting statutes, are intended to be the minimum requirements for reasonable safety. Nothing prevents you from adding more layers for more safety, if the budget and schedule allow.