Smoke Alarm Count and Placement (IRC R314)
Two halves people confuse. The COUNT is additive and gets undercounted: one 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 depends entirely on the SENSING TYPE, and the spread is better than three to one: 20 ft horizontally from a permanently installed cooking appliance for ionization, 10 ft for ionization with a silencing switch, and 6 ft for photoelectric or an alarm marked to reduce cooking nuisance alarms. So an alarm 8 ft from the range fails as ionization and passes as photoelectric -- in an open plan, changing the type is usually the only way a required location works, and far cheaper than moving it. Also the 3 ft separation from a tub/shower bathroom door.
Formula and source
minimum alarms = sleeping rooms + separate sleeping areas + additional stories; required cooking clearance = 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.
IRC R314.3 Location and R314.3.1 Installation near cooking appliances.
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