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Home / Code Guides / Smoke & CO Alarms

Smoke & Carbon Monoxide Alarm Placement — Where the Code Puts Them

Smoke alarm placement in a dwelling is a fixed list: each bedroom, outside each sleeping area, and every story. Carbon monoxide alarms attach to the same permit triggers whenever the home has fuel-fired appliances or an attached garage.

SMOKE AND CO ALARM PLACEMENT — FLOOR PLAND25BEDROOMBEDROOMHALL / SLEEPING AREALIVINGGARAGEcooking applianceSSSCO+ SMOKE ALARM ON EACH ADDITIONAL STORY, INCLUDING BASEMENTS AND HABITABLE ATTICSRULES · IRC 2021 §R314.3 / §R314.4 / §R315.3Ssmoke alarmCOcarbon monoxide alarmSmoke alarms: in each sleeping room; outside each separate sleeping area in the immediate vicinity of the bedrooms; oneach additional story, including basements and habitable attics (§R314.3).Smoke alarms 3 ft MIN horizontally from the door of a bathroom with a tub or shower, unless that would prevent placing arequired alarm (§R314.3).From a permanently installed cooking appliance: ionization alarms 20 ft MIN, with a silencing switch 10 ft MIN,photoelectric 6 ft MIN (§R314.3.1).All smoke alarms in a dwelling unit are interconnected so one alarm activates all; listed wireless alarms may be used(§R314.4).CO alarms: outside each separate sleeping area near the bedrooms, and in a bedroom that has a fuel-burning appliance init or its attached bathroom (§R315.3). Where required: §R315.2.Combination smoke and CO alarms may replace either type (§R314.5, §R315.4). Listings: CO alarms listed to UL 2034;combination alarms to UL 217 and UL 2034 (§R315.1.1).Not to scale. Plan is illustrative.ALARMS · IRC 2021 §R314.3 · §R314.3.1 · §R314.4 · §R315.2 · §R315.3
Smoke and carbon monoxide alarm placement — IRC 2021 R314 / R315.Open full diagram →
RequirementModel Code StandardSection
Smoke alarms — in bedroomsOne in each sleeping roomIRC R314.3
Smoke alarms — outside bedroomsOne outside each separate sleeping area, in the immediate vicinity of the bedroomsIRC R314.3
Smoke alarms — every storyAt least one per story including basements and habitable atticsIRC R314.3
Interconnection & powerHardwired with battery backup and interconnected so all sound together; listed wireless interconnection allowedIRC R314.4, R314.5
CO alarms — whereOutside each separate sleeping area, and required when the dwelling has fuel-fired appliances or an attached garage; in bedrooms when a fuel-fired appliance is in the bedroom or its bathroomIRC R315.2, R315.3
Alterations triggerInterior alterations, repairs, or additions requiring a permit bring the whole dwelling up to smoke/CO alarm requirements (battery-only allowed where no wiring access)IRC R314.2.2, R315.2.2
Kitchen/bath spacingIonization alarms not within 20 ft of a permanent cooking appliance (10 ft with a silencing feature); photoelectric alarms not within 6 ft; not within 3 ft of bath doors with tub/showerIRC R314.3.1

Worth knowing

  • The alterations trigger surprises homeowners: a simple permitted remodel means alarms in every bedroom of a 1970s house.
  • NFPA 72 governs installation details the IRC references — ceiling placement, distance from walls, and sloped-ceiling rules come from there.
  • Many states layer their own CO statutes on top of the IRC, including rental-property requirements.
  • Combination smoke/CO units are permitted and are the practical answer for the outside-sleeping-area location.

Common questions

What does the code say about smoke alarms — in bedrooms for Smoke & CO Alarms?

One in each sleeping room. (IRC R314.3)

What does the code say about smoke alarms — outside bedrooms for Smoke & CO Alarms?

One outside each separate sleeping area, in the immediate vicinity of the bedrooms. (IRC R314.3)

What does the code say about smoke alarms — every story for Smoke & CO Alarms?

At least one per story including basements and habitable attics. (IRC R314.3)

Adopted edition by state

Base-code year from BuildSpec’s adoption records. States often amend the base code, and your city or county may differ, so confirm with your building department.

Related sections and guides

This guide is BuildSpec’s own summary, not code text. It cites the 2021 International Residential Code and the 2023 National Electrical Code as model standards. The IRC 2021 text itself is in the Code Library for signed-in members; BuildSpec publishes no NEC text, which is at nfpa.org.Neither is an adoption record: your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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