Fire Alarm Audibility in Ontario: How Loud It Has to Be

Quick answer

Read this before you use any number here

Ontario's Building Code is now O. Reg. 163/24: a regulation one page long. It adopts NBC 2020 as amended by the "Ontario Amendments to the National Building Code of Canada 2020."

The amendment document actually in force is dated 17 July 2026, and MMAH does not publish it online. It is sent on email request only, from Ontario.Amendment.Document@ontario.ca.

The free text you can open right now is the 2024 Building Code Compendium (Vol. 1 · Vol. 2), the January 16, 2025 Update (Containing O. Reg. 5/25). That consolidation sits four amendment-document versions behind the one in force. Everything quoted below is from it, and every quote is marked as such.

The article number moved too. Audibility is 3.2.4.18 in the 2024 Code. Under the revoked O. Reg. 332/12 it was 3.2.4.20. Ontario renumbered Subsection 3.2.4 to match NBC 2020, and the shift is not uniform; this article moved by two, others by one or not at all, so do not apply a flat −2 to any other number. The full map is in Ontario vs the National Building Code. An older document citing 3.2.4.20 for audibility is not wrong, it is just old. More on editions and what is in force in which ULC edition applies.

The floor area minimum: 65 dBA, and 10 above ambient

Sentence 3.2.4.18.(7), verbatim from the Compendium:

Except as required by Sentence (5), the sound pressure level from a fire alarm system's audible signal device within a floor area shall be not less than 10 dBA above the ambient noise level and not less than 65 dBA, when any intervening doors between the device and the rest of the floor area are closed.

Three things are doing work in that sentence.

It is two tests, not one. You have to clear 65 dBA and clear ambient by 10. In a quiet corridor the 65 dBA floor governs. In a plant room running at 70 dBA, 65 is a fail; you need 80.

Which means the ambient level is an input, not a footnote. You cannot settle audibility off a drawing. You need to know what each space sounds like with its equipment running.

Doors closed. The measurement condition is written into the requirement. A level taken with the door open is not the level the Code asks for.

Sleeping rooms: 75 dBA, doors closed

Sentence 3.2.4.18.(5), verbatim:

The sound pressure level in a sleeping room from a fire alarm audible signal device shall be not less than 75 dBA in a building of residential occupancy when any intervening doors between the device and the sleeping room are closed.

Ontario and the national code differ here. NBC 2020 reads "in a building of residential or care occupancy." Ontario's Compendium text says residential occupancy only.

So on the face of the printed Ontario text, a sleeping room in a care occupancy is not caught by the 75 dBA sentence. What remains for it is the general floor-area rule in Sentence (7) (10 above ambient and not less than 65 dBA) plus whatever the design, the specification or the AHJ requires. If you are working on a care occupancy, raise this with the AHJ rather than assuming either number.

Low frequency in sleeping rooms: new, and with no frequency attached

Sentence 3.2.4.18.(6), verbatim:

Audible signal devices in sleeping rooms in a building of residential or care occupancy shall emit a low frequency signal.

That is the entire requirement. The Code sets no frequency.

The only figure anywhere near it is a non-mandatory Appendix A note, Vol. 2 printed page 42:

A-3.2.4.18.(6) Low Frequency Signal. Audible signal devices that emit a low frequency signal in the range of 470 Hz to 570 Hz have been shown to be more effective in waking people.

Two things follow that are worth being blunt about.

520 Hz appears nowhere in Ontario's Building Code. It is the NFPA 72 figure (American) and it happens to be the centre of the 470 to 570 Hz band in the appendix note. Devices are marketed on it and specs are written around it, but Ontario law does not state it. If 520 Hz is binding on your project, it is binding because a specification or a listing says so, not because the Code does.

This requirement is new in the 2024 Code. The string "low frequency signal" appears nowhere in the revoked O. Reg. 332/12. If you learned in-suite audibility under the old code, this is a genuinely new obligation, not a re-lettered old one.

And note the scope mismatch. Sentence (6) covers residential or care occupancy. Sentence (5)'s 75 dBA floor covers residential only. Same subject, two different scopes, one article apart.

The maximum: the printed text contradicts itself

This is the part worth your attention, because the free text does not resolve it.

Sentence 3.2.4.18.(4), verbatim from the Compendium:

(4) In all normally occupied spaces, the fire alarm signal sound pressure level (a) shall be not more than 110 dBA when measured at a distance of 3 m from the device, or (b) is permitted to be more than 100 dBA provided the sound pressure level measured 2 000 mm above floor level is not more than 100 dBA.

Read clause (b) against clause (a). Clause (b) grants relief from a 100 dBA ceiling. Clause (a) does not state a 100 dBA ceiling; it states 110. The relief has nothing to attach to.

Here is where the 100 comes from. The revoked O. Reg. 332/12's equivalent, Article 3.2.4.20.(4)(a), read:

not more than 100 dBA when measured at a distance of 3 m from the device

With 100 in clause (a), the pair reads coherently: a 100 dBA ceiling at 3 m, with an alternative that lets you exceed it provided you hold 100 dBA at head height. Ontario appears to have amended clause (a) alone and left the pair incoherent.

And NBC 2020 has neither clause. It reads simply:

The fire alarm signal sound pressure level shall be not more than 110 dBA in any normally occupied area.

No 3 m basis, no 2 000 mm alternative, no clause structure.

What we are not going to do is tell you which number is correct. We do not know. Three readings are all defensible from the documents available: that clause (a) is the current requirement and clause (b) is a leftover; that the amendment document in force has since fixed the pair; or that the intent was to align with NBC's flat 110 dBA and the clause structure survived by accident.

What to do about it. The operative Amendment Document is dated 17 July 2026 and is not published online. If a maximum figure matters on your project (an assembly space, a plant room, anywhere you are pushing device output) request the current amendment document from Ontario.Amendment.Document@ontario.ca, read Article 3.2.4.18 in it, and confirm with your AHJ. That is a one-email question, and it is a better answer than anything you can get from a summary site, including this one.

Suites with smoke detectors instead of smoke alarms

Where smoke detectors are installed in lieu of smoke alarms, Sentence 3.2.4.20.(10)(a) requires that they be

capable of independently sounding audible signals with a sound pressure level between 75 dBA and 110 dBA within the individual suites

That is a bracketed range, both ends stated, and it sits in a different article from the general audibility rules.

Temporal pattern

Smoke alarm sound patterns must, per Sentence 3.2.4.20.(16), either

• (a) meet the temporal patterns of alarm signals, or
• (b) be a combination of temporal pattern and voice relay.

Where strobes come in instead

Article 3.2.4.19, "Visible Signals", Sentence (1) requires visible signal devices in addition to audible ones (not as a substitute) including:

• (b) in assembly occupancies in which music and other sounds associated with performances could exceed 100 dBA
• (c) in any floor area in which the ambient noise level is more than 87 dBA
• (d) in any floor area in which the occupants (i) use ear protection devices, (ii) are located in an audiometric booth, or (iii) are located in sound-insulating enclosures

Ontario also carries clause (1)(i), requiring visible signals in living spaces in a suite of residential occupancy in a Group C major occupancy apartment building. NBC 2020 has no such clause: that one is Ontario's own addition, and it is the clause most likely to be missed by anyone designing from the national code.

Intelligibility has no number in the Code

Articles 3.2.4.22.(1)(b) and 3.2.4.23.(2)(b) require voice messages to be "audible and intelligible in all parts of the building." That is the whole standard of performance.

Appendix Note A-3.2.4.22.(1)(b) explains what intelligible means: that a person with average hearing and cognitive abilities can understand the transmitted messages. It goes on to say there is no absolute measure to predetermine the effect of loudspeakers, and that it may be necessary, once the building is furnished and occupied, to add loudspeakers to improve message quality. It cites ISO 7731 as suggesting a level at least 15 dBA above ambient.

There is no Common Intelligibility Scale value anywhere in Ontario's Building Code. We searched both Compendium volumes (2,261 pages) for "Common Intelligibility" and for "CIS." Zero hits.

So if a 0.70 CIS target is being applied on your project, it is coming from CAN/ULC-S524 or from the project specification. It is not coming from the Building Code, and saying "code requires 0.70 CIS" in a report is wrong.

What the Code does not tell you

The Building Code gives you levels and the conditions they are measured under. It does not give you:

• how to take the measurement: meter, weighting, position, dwell
• device spacing and layout
• how much level you lose through a closed door

All of that lives in CAN/ULC-S524, which is a paywalled standard. We are not going to guess at its contents or reproduce them from an unlicensed copy. If you need those procedures, you need the standard, through your employer, a library subscription, or purchase. What each of the four ULC standards covers is set out in S524, S537, S536 and S1001 explained.

Everything above is Building Code; it governs what gets installed and verified. Duties for systems already in service sit under the Fire Code, a separate regime: see the Ontario Fire Code for technicians.

How to check any of this yourself, free

1. 2024 Building Code Compendium Vol. 1 and Vol. 2: $0.00 from Publications Ontario. Division B Article 3.2.4.18 is in Vol. 1; the Appendix A notes are in Vol. 2. This is the January 16, 2025 consolidation.
2. NBC 2020 from NRC: free, no registration. Use it to see what Ontario changed.
3. The amendment document in force: email Ontario.Amendment.Document@ontario.ca. Dated 17 July 2026. This is the only way to see the current text, and the only way to settle the maximum.
4. Your AHJ: on the care occupancy scope and on the maximum, before it costs you a rejected verification.

Sources checked August 2026. Quotations are from the 2024 Building Code Compendium, January 16, 2025 Update (Containing O. Reg. 5/25), the most recent free consolidated Ontario text. The amendment document in force is dated 17 July 2026 and is not published online.

General information, not compliance advice. Confirm the edition in force for your project with your authority having jurisdiction.

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