Smoke Alarm Count and Placement (IRC R310)
Two halves people confuse. The COUNT is additive and gets undercounted.
Example
You enter
- Sleeping rooms 3
- Separate sleeping areas (one alarm outside each) 1
- Additional stories, incl. basements and habitable attics 1
- Sensing type (sets the distance under IRC 2021) ionization
- Horizontal distance to the cooking appliance (ft) 8
- Horizontal distance to a tub/shower bathroom door (ft; 0 to skip) 4
- IRC edition 2021
You get
- Minimum alarm count 5
- Required cooking (ft) 20
- Cooking deficit (ft) 12
- Bathroom separation 0
Checked against published worked examples from: International Code Council.
Details, formula, and sources
ScopeOne in each sleeping room, one OUTSIDE each separate sleeping area, and one on each additional story including basements and habitable attics -- three bedrooms, one sleeping area, one extra story is five, minimum. The CLEARANCE from a permanently installed cooking appliance depends on the code edition: the 2024 IRC sets 10 ft for every alarm, 6 ft only where 10 ft would block a required location; the 2021 IRC set it by sensing type -- 20 ft ionization, 10 ft ionization with a silencing switch, 6 ft photoelectric or nuisance-listed -- so there a type change could fix a failing spot. Also the 3 ft separation from a tub/shower bathroom door.
Formula or tableminimum alarms = sleeping rooms + separate sleeping areas + additional stories; required cooking clearance = 10 ft for any sensing type, or 6 ft where 10 ft would prevent a required location (IRC 2024, the default); under IRC 2021, 20 ft (ionization), 10 ft (ionization with a silencing switch), or 6 ft (photoelectric, or marked to reduce cooking nuisance alarms); bathroom separation = 3 ft horizontally from the door or opening of a bathroom with a tub or shower.
Source and editionIRC 2024 R310.3 [R314.3 in IRC 2021] Location and R310.3.1 [R314.3.1 in IRC 2021] Installation near cooking appliances; the IRC 2021 cooking distances are selectable.
Free accessBoth provisions are short prescriptive sentences reproduced in state adoptions and building-department bulletins. No table is reproduced.
What governsEstimate. AHJ and licensed professional govern.
API field namessleeping_rooms, sleeping_areas, additional_stories, alarm_type, distance_to_cooking_ft, distance_to_bath_door_ft, code_edition, required_alarms, required_cooking_ft, cooking_deficit_ft, bath_deficit_ft
- Count each sleeping room + outside each separate sleeping area + each additional storyIRC R310.3 [R314.3 in IRC 2021]
- Story exclusions crawl spaces and uninhabitable attics do not countIRC R310.3 [R314.3 in IRC 2021]
- Cooking clearance (IRC 2024, default) 10 ft for any sensing type; 6 ft only where 10 ft would prevent a location R310.3 requiresIRC 2024 R310.3.1
- Cooking clearance (IRC 2021, selectable) 20 ft ionization, 10 ft ionization with silencing, 6 ft photoelectric or nuisance-listedIRC 2021 R314.3.1
- Bathroom 3 ft horizontally from the door or opening of a bathroom with a tub or showerIRC R310.3 [R314.3 in IRC 2021]
- Exception the bathroom separation (and, under 2021, the cooking distances) yield where they would prevent a required location - a documented last resortIRC R310.3 [R314.3 in IRC 2021] / IRC 2021 R314.3.1
- Not checked CO alarms, interconnection, power and battery backup, mounting geometry, existing-dwelling triggersstated scope limit