Smoke and CO Alarm Requirements Your Permit Triggers

Why this matters

A permitted bathroom remodel can fail its final inspection over a bedroom the crew never entered. The residential code ties smoke and carbon monoxide alarm requirements to the permit itself: when permitted work happens in an existing dwelling, the whole dwelling unit has to be brought up to the alarm requirements for a new house, not just the room you worked in. The work is modest; the surprise is not. A customer who learns at final inspection that four more alarms are needed, and that the inspector will not sign off until they are in, remembers the shop that did not mention it.

The rule and its trigger

In the 2021 IRC, as adopted by your jurisdiction, two parallel provisions carry this:

• Smoke alarms (R314.2.2). Where alterations, repairs or additions requiring a permit occur, or where sleeping rooms are added or created, the individual dwelling unit must have smoke alarms located as required for new dwellings.
• Carbon monoxide alarms (R315.2.2). Where work requiring a permit occurs in an existing dwelling that has an attached garage or contains a fuel-fired appliance, CO alarms must be provided as required for new dwellings.

The trigger is the permit, not the size of the work. A small permitted job reaches the whole unit; a large job that needs no permit reaches nothing under these sections. Section numbers and exception wording have moved between editions, and some states amend these sections when they adopt the IRC, so read the text in the edition on your permit. See related: The Edition on the Permit, Not the Newest Edition.

The exceptions, and the asymmetry that catches HVAC shops

Both provisions exempt work on the exterior surfaces of the dwelling: roofing, siding, adding or replacing windows or doors, adding a porch or deck. The reasoning is that exterior work does not change the inside of the house and the inspector does not need to enter it.

The second exception is where the two provisions differ, in the 2021 text:

• The smoke alarm provision exempts the installation, alteration or repair of plumbing or mechanical systems.
• The CO alarm provision exempts only noncombustion plumbing or mechanical systems.

So a permitted furnace or gas water heater replacement is exempt from the smoke alarm upgrade and not exempt from the CO alarm upgrade. That is deliberate: installing a combustion appliance is exactly the work that creates CO risk. A heat pump or electric water heater replacement is noncombustion and exempt from both. An attached garage does not change that exemption; it only makes the house one that needs CO alarms when some other, non-exempt permitted work happens inside it.

Electrical permits are not named in either exception in the 2021 text, and jurisdictions differ on whether they enforce the alarm trigger on electrical-only permits. Ask the building department, once, and write down the answer. See related: How to Document a Code Interpretation You Were Given.

Where the alarms have to be

"As required for new dwellings" points back to the location rules for new construction. In the 2021 IRC, paraphrased:

The code also sets placement offsets, such as distance from a cooking appliance and from a bathroom door, that matter on the day of install; follow the alarm maker's instructions together with the code. Alarms must be listed: smoke alarms to UL 217, CO alarms to UL 2034, combination units to both. The installation side of NFPA 72 is referenced by the IRC and binds through that adoption.

Power and interconnection in existing areas

New construction wants alarms hardwired with battery backup and interconnected so one sounding sets off all. For existing areas, the 2021 IRC relaxes both requirements where the alterations or repairs do not remove interior wall or ceiling finishes exposing the structure, unless an attic, crawl space or basement is available that could provide access for hardwiring and interconnection without removing finishes. The same edition allows listed wireless interconnection in place of physical wiring where every alarm sounds when one activates.

That "unless" decides the price. An accessible attic over the bedrooms can mean the inspector expects hardwired, interconnected alarms there even though no bedroom wall was opened. Inspectors differ on what "available" means; this is a question for the building department before the quote, not at final. Hardwiring alarms is circuit work: de-energize and lock out the circuit, and prove it dead on a known live source before and after (NFPA 70E Article 120 (120.5 in the 2021 edition, renumbered in 2024), with work practices at 29 CFR 1910.333(b)(2)).

Existing alarms that are past their service life do not count toward the requirement. Manufacturers' instructions and NFPA 72, as adopted, call for replacing smoke alarms 10 years from their date of manufacture, which is printed on the back, and CO alarms at the end of life their maker states. Inspectors check the date.

Why it belongs in the quote

The alarm work is small in hours and large in friction. Left out, it surfaces at final inspection, after the customer has paid most of the job, as a demand for more work they did not agree to, and the shop either eats it or argues over it with the job still open. Put in, it is a line item the customer can see, with the reason stated, and the inspector's checklist matches the invoice.

This is what it looks like on the estimate:

LINE 7  Smoke/CO alarm upgrade (required by permit)
        Code: IRC R314.2.2 / R315.2.2 as adopted
        Add smoke alarm: bedroom 1, 2, 3, basement  x4
        Replace hall alarm w/ smoke+CO combo        x1
        Hall alarm (2014 mfg date) past service life
        Interconnect: listed wireless (confirm w/ AHJ)
        Note: inspector checks all alarms at final

Worked example: a bathroom remodel and a furnace swap in the same house

The house: two stories plus a basement, three bedrooms on the second floor off one hallway, a gas furnace, and an attached garage. Existing alarms: one smoke alarm in the upstairs hall and one on the first floor. Jurisdiction on the 2021 IRC with no amendment to these sections.

Job 1: hall bathroom remodel under a building permit. Not exterior work and not plumbing-only work (the tile, drywall and vanity are building work), so both provisions apply. Smoke alarms required: 3 bedrooms at 1 each is 3, plus 1 outside the sleeping area, plus 1 on the first floor, plus 1 in the basement, for 6. The existing hall alarm covers the sleeping-area location and the first-floor alarm covers that story, so 2 of the 6 exist and 4 are added: the three bedrooms and the basement. CO alarms: the furnace and the attached garage each make the house one that needs them; one is required outside the sleeping area, and no fuel-burning appliance is in a bedroom, so the count is 1.

Then the date check. The hall alarm was made in 2014, and 2014 plus 10 is 2024, so in 2026 it is past its service life and no longer counts. It is replaced with a combination smoke and CO alarm, which fills both the sleeping-area smoke location and the single CO location. The new-alarm count becomes 5: four smoke alarms and one combination unit. The attic over the bedrooms is accessible, so the quote assumes the inspector may expect interconnection and prices listed wireless interconnected alarms, with the question noted for the building department.

Job 2: furnace replacement under a mechanical permit, a year later. A fuel-fired appliance installation is not "noncombustion", so the CO provision applies; it is mechanical work, so the smoke provision does not. The house already has the combination alarm outside the sleeping area from Job 1, so the CO requirement is met and nothing is added. If Job 1 had never happened, this job would add one CO alarm outside the bedrooms and no smoke alarms at all, and a shop that priced smoke alarms on it would be quoting work the code does not require.

What changes the answer. In a state that amended R314.2.2 or R315.2.2 when adopting, the triggers or exceptions may differ in either direction; a few jurisdictions also require alarms at sale or for rentals regardless of permits. See related: Grandfathered Is Not a Permanent Status. In a jurisdiction still on an edition before CO alarm requirements reached existing dwellings in this form, Job 2 would add nothing. Read the adopted text.

How to verify you got this right

• The quote states whether the job's permit triggers the smoke provision, the CO provision, both, or neither, and which exception applies if any.
• The alarm count is laid out by location, bedroom by bedroom, story by story, with existing alarms credited only where they are in a required location and inside their service life.
• The manufacture date on every existing alarm you are crediting was read off the unit, not assumed.
• The power and interconnection assumption is written down, with the building department's answer on "available access" recorded.
• At final, every alarm sounds when its test button is pressed, and with interconnection, every alarm sounds when any one is tested.

References

• International Residential Code, 2021 edition, R314 and R315, as adopted by your jurisdiction
• UL 217 (smoke alarms) and UL 2034 (CO alarms), and NFPA 72 as referenced by the adopted IRC
• Alarm manufacturers' installation instructions
• See related: The Alarms the Permit Required and Nobody Quoted; Handling Inspector-Required Extras and Who Pays; Smoke and CO Detector Install Reference