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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 & CO ALARM PLACEMENT — FLOOR PLAND25BEDROOM 1BEDROOM 2HALL / SLEEPING AREALIVINGGARAGE(attached)fuel applianceSSSCOSSMOKE + CO OUTSIDE EACH SLEEPING AREA+ SMOKE ALARM ON EVERY ADDITIONAL STORY, INCLUDING BASEMENTS & HABITABLE ATTICSRULES · IRC 2021 §R314 (SMOKE) / §R315 (CARBON MONOXIDE)SSmoke: in each sleeping room · outside each sleeping area · on every story incl. basement (§R314.3)COCO: outside each sleeping area where fuel-fired appliances exist or garage is attached (§R315.3)Hardwired with battery backup + interconnected (new construction, §R314.4–.6) · Listed UL 217 / UL 2034Keep smoke alarms ≥ 3 ft from bathroom doors with tub/shower and ≥ 10 ft (ionization) from cooking appliances (§R314.3.3)NOT TO SCALE
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.
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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