Smoke alarms required in all King County dwellings per WA Building Code (RCW 19.27, IRC R314). New construction needs hardwired interconnected alarms with battery backup; battery-only allowed in existing homes.
Washington State adopts the International Residential Code with amendments; RCW 19.27 establishes the statewide building code enforced locally. IRC Section R314 as amended requires smoke alarms in every sleeping room, outside each sleeping area within 10 feet of bedroom doors, and on every story including basements. New construction after 2010 requires hardwired 120V alarms with battery backup, interconnected so all sound when any detect smoke. Existing homes being sold or substantially altered must be upgraded to meet current code at the time of permit. Battery-only alarms remain legal in existing homes not undergoing remodel. Carbon monoxide alarms are required under RCW 19.27.530 in all dwellings with fuel-burning appliances or attached garages since 2013. King County Fire Marshal (206-296-6600) enforces fire code in unincorporated areas. Rental properties must certify working smoke and CO alarms at tenant turnover per RCW 59.18.060. 10-year sealed-battery alarms satisfy requirements in existing homes under the 2018 state amendment.
Misdemeanor under RCW 19.27.097 for building code violations, fine up to 1,000 dollars. Landlord failure to provide working alarms can result in tenant remedies under RCW 59.18 including rent abatement.
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