Low Frequency Notification in Residential Occupancies – A Change to the 2021 IBC

The occupancy of a space plays a major role in fire alarm system design; each type has different requirements for system initiation/activation and occupant notification. The types and quantities of fire alarm initiating devices needed for a self-storage warehouse are different from those needed for an office building. The types of occupant notification appliances needed to serve a large assembly space are much different from those needed in a hospital. However, some of the most distinctive and complicated occupancies relative to fire alarm design in the International Building Code (IBC) are Group R-1 (transient residential occupancies) and Group R-2 (permanent residential occupancies). When dealing with these occupancies, the fire alarm requirements can be daunting and therefore easily missed. This is particularly true of the requirements surrounding low frequency notification.

Low frequency notification (producing a low frequency tone of 520 Hz ± 10 percent) is used to alert occupants that are asleep or are hard-of-hearing. Research has indicated that low frequency tones are six times as effective as the more standard 3kHz signal when it comes to waking high-risk occupants (such as people over 65 who are hard of hearing, school-age children, and people who are alcohol impaired).

IBC Section 907 generally requires Residential occupancies to be provided with fire alarm systems designed and installed in accordance with NFPA 72, National Fire Alarm & Signaling Code (IBC Section 907.2). In Group R-1 and R-2 occupancies, notification for building fire alarm system activation and notification for local in-unit smoke detector activation are governed by separate requirements.

For notification of a building fire alarm system activation, Group R-1 and R-2 occupancies must be provided with (IBC Sections 907.5.2.1 and 907.5.2.3): Audible appliances (typically system speakers and/or horns) to provide notification to all occupiable spaces within the building; and visible appliances in all common areas. As well as, in Massachusetts, locations required by 521 CMR, Architectural Access Board. From Chapter 18 of NFPA 72, all audible notification appliances serving sleeping areas must produce a low frequency tone.

A separate requirement typically applies for notification of smoke detector/alarm activation within a residential unit. Chapter 29 of NFPA 72 (specifically Section 29.3.8 and associated subsections) requires low frequency tones where notification appliances are provided voluntarily for those with hearing loss or are required by other governing laws, codes, or standards for people with hearing loss. In Massachusetts, 521 CMR Sections 8.6 and 9.7 provide scoping for areas where such appliances must be provided. Specifically: In permanent residential occupancies, 2% of the total units must be provided with features for hearing impaired persons; and in transient residential occupancies the quantity of units that must be designated as hearing impaired varies proportional to the number of guest rooms in the building (in accordance with the table in 521 CMR Section 8.4.5).

Why is this important?

In Massachusetts, the current (9th Edition) 780 CMR, Massachusetts State Building Code is based on the 2015 Edition of the IBC. However, the 10th Edition of 780 CMR is currently being developed and will be based on the 2021 Edition of the IBC (skipping the 2018 Edition).

Under the 2015 IBC, the requirements for low frequency notification discussed above are all currently located in referenced standards (NFPA 72, 521 CMR), not directly within the building code. The revamped content in the 2021 IBC will now include much of this scoping for low frequency tones directly within the body of Section 907.5.2. While this minor change should simplify finding and understanding these requirements, there was a more impactful change in the body of the 2021 IBC as well: The IBC (2021) will now require low frequency notification to be provided for all residential units upon activation of smoke detectors/alarms in that unit, where this would have only been required in hearing impaired units under previous editions. This requirement would take precedence over the language and scoping of NFPA 72 and 521 CMR, in accordance with the Applicability section of 2021 IBC. This is a significant change as there are limited options on the market to purchase notification appliances capable of producing low frequency tones other than those devices listed to be part of the fire alarm system.

There are of course many other fire alarm system requirements for residential (and all other) occupancies. Please feel free to contact the Code Red office for more information by emailing as at info@crcfire.com!



Application of any information provided, for any use, is at the reader’s risk and without liability to Code Red Consultants. Code Red Consultants does not warrant the accuracy of any information contained in this blog as applicable codes and standards change over time. The application, enforcement and interpretation of codes and standards may vary between Authorities Having Jurisdiction and for this reason, registered design professionals should be consulted to determine the appropriate application of codes and standards to a specific scope of work.