Carbon monoxide detector requirements in Washington State apply to nearly every home: single-family houses, duplexes, apartments, condominiums, hotels, and motels all need CO alarms outside each sleeping area and on every level if the building has any fuel-burning appliance or an attached garage.1Washington State Legislature. RCW 19.27.530 Carbon Monoxide Alarms – Requirements – Exemptions – Adoption of Rules The rule has been in force since January 1, 2013 for existing buildings and since 2011 for new construction, and it is codified in RCW 19.27.530 with technical details in WAC 51-50-0915.
Which Homes Need CO Alarms
The trigger is simple. If a dwelling unit contains a furnace, water heater, gas stove, wood-burning fireplace, or any other fuel-burning appliance, or if it has an attached garage, CO alarms are required.1Washington State Legislature. RCW 19.27.530 Carbon Monoxide Alarms – Requirements – Exemptions – Adoption of Rules Most Washington homes meet at least one of those conditions, so the requirement applies broadly.
Individual units inside larger buildings can escape the requirement, but only when three conditions are true at the same time: the unit contains no fuel-burning appliance and no attached garage, it is not next to a room that has one, it does not share ductwork or ventilation with such a room, and the building has a common-area carbon monoxide detection system.1Washington State Legislature. RCW 19.27.530 Carbon Monoxide Alarms – Requirements – Exemptions – Adoption of Rules Miss any one of those and the exemption is gone.
Where to Install Them
Under the state building code, CO alarms must be placed outside each separate sleeping area, in the immediate vicinity of the bedrooms, and on every level of the home, including basements. The purpose is to wake sleeping occupants before CO reaches dangerous concentrations. An alarm sitting only on the furnace floor, with none near the bedrooms, does not meet the code and does not protect the people it is supposed to protect. Carbon monoxide is roughly the same weight as air and moves through a house on air currents and ductwork, so it reaches upper floors readily.
Alarms can be battery-operated, hardwired with battery backup, or plug-in with battery backup.2Washington State Department of Health. Carbon Monoxide Hardwired units with battery backup are the most reliable choice because they keep working through power outages. Combination smoke/CO alarms are allowed if they meet the standards for both. All CO alarms should be listed to UL 2034, the national safety standard for residential units.
Who Is Responsible for Maintenance
This is where the Washington rule catches people off guard. In a rental, the statute assigns ongoing maintenance to the tenant, not the landlord. RCW 19.27.530 directs the building code rules to require the tenant to maintain the alarm, including battery replacement, according to the manufacturer’s instructions.1Washington State Legislature. RCW 19.27.530 Carbon Monoxide Alarms – Requirements – Exemptions – Adoption of Rules
The practical breakdown:
- Landlords must provide and install working CO alarms before the tenant moves in.
- Tenants must keep the alarms working during the tenancy: test them, replace batteries, and follow the manufacturer’s schedule. Notify the landlord in writing for anything beyond routine battery changes, and never remove or disable the device.
- Homeowners handle everything themselves, from purchase through replacement.
Most manufacturers recommend testing monthly and replacing the entire unit every five to seven years. Check the date printed on your alarm. A CO detector past its expiration may not sound even when gas is present.
Selling an Older Home
Washington carves out an exemption for older owner-occupied homes, and it disappears at the closing table. If you owned and lived in a single-family home that was legally occupied before July 26, 2009, you are not required to have CO alarms while you live there. Once you sell, the exemption ends. The seller must install CO alarms meeting the current state building code before the buyer or anyone else can legally occupy the home.1Washington State Legislature. RCW 19.27.530 Carbon Monoxide Alarms – Requirements – Exemptions – Adoption of Rules
The seller disclosure form under RCW 64.06.020 includes a specific question about whether the property has CO alarms and references the seller’s obligation under RCW 19.27.530.3Washington State Legislature. RCW 64.06.020 Improved Residential Real Property – Seller’s Duty Buyers should confirm the alarms are actually installed, not just disclosed. Real estate brokers are not liable for a seller’s failure to comply; the duty sits with the property owner.1Washington State Legislature. RCW 19.27.530 Carbon Monoxide Alarms – Requirements – Exemptions – Adoption of Rules
Full List of Exemptions
- Dwelling units with no fuel-burning appliance and no attached garage. All-electric homes without garages are the common example.
- Owner-occupied single-family homes legally occupied before July 26, 2009, but only while the same owner lives there. The exemption ends on sale.1Washington State Legislature. RCW 19.27.530 Carbon Monoxide Alarms – Requirements – Exemptions – Adoption of Rules
- Individual units in larger buildings that meet all three conditions above: no fuel-burning appliance in or adjacent to the unit, no shared ductwork with a room that has one, and a common-area CO detection system in the building.
- Categories the State Building Code Council has determined do not need alarms to protect occupant health.1Washington State Legislature. RCW 19.27.530 Carbon Monoxide Alarms – Requirements – Exemptions – Adoption of Rules
Even if your home qualifies, installing an alarm is still a sensible precaution. A portable generator during a power outage, a future appliance change, or CO drifting from an adjacent unit can all create a hazard the exemption did not anticipate.
What Happens If You Don’t Comply
The statute does not set a specific fine for homeowners or landlords who skip the alarms. Enforcement runs through local building departments, and violations can result in enforcement actions, failed inspections, or complications during a sale. For landlords the larger exposure is civil. Washington landlords owe tenants a safe and habitable rental. Failing to install a CO alarm required by state law is strong evidence of negligence if a tenant is later poisoned, and it can support a claim for medical expenses, lost income, and pain and suffering. Photos showing no alarm was installed, or records showing skipped inspections, are the kind of documentation that establishes the breach. The alarms themselves usually cost under $100.
Check Local Rules Before You Stop
The state requirements are a floor, not a ceiling. Washington cities and counties can and do adopt stricter rules, and some require CO alarms in all residential units regardless of whether a fuel-burning appliance is present.2Washington State Department of Health. Carbon Monoxide Call your city or county building department, or your local code official, to confirm what applies to your address before you rely on a state-level exemption.