Bellingham Real EstateLummi IslandWhatcom County Real Estate June 21, 2018

Understanding the Washington State Carbon Monoxide Alarm Laws

RCW 19.27.530 (2009) and Chapter 132 Laws of 2012 (SSB 6472)

Carbon monoxide (CO) is a poisonous gas that cannot be seen or smelled and can kill a person in minutes. Carbon monoxide can quickly build up to unsafe levels in enclosed or semi-enclosed areas. Carbon monoxide killed over 1,000 Washington residents between 1990 and 2005. In the aftermath of the December 2006 windstorm, over 300 people were treated at hospital emergency rooms for CO poisoning and eight people died. Generators in garages, or near air intakes, and use of charcoal or gas grills indoors, are common causes of CO poisoning during power outages. Fuel burning appliances, attached garages, and fireplaces are also sources of CO.

Beginning January 1, 2011, state law required CO alarms to be installed in

all new single family homes and residences, including apartments, condominiums, hotels, and motels.

State law requires CO alarms be installed in

existing apartments, condominiums, hotels, motels and single-family residences by January 1, 2013.

Owner-occupied single-family residences, legally occupied before July 26, 2009, are not required to have CO alarms until they are sold.

The seller is required to equip the residence with CO alarms before any other person legally occupies the home. Substitute Senate Bill 6472 added CO alarms to the Purchase/Sale disclosure form in 2012.


SSB 5561, implemented as RCW 19.27.530, charged the State Building Code Council with adoption of administrative rules (WAC 51-50-0908) to implement the carbon monoxide alarm law and consider exemptions for some building classifications. Sleeping units or dwelling units in new or existing motels, hotels, college dormitories, and DSHS licensed boarding home and residential treatment facilities, which do not themselves contain a fuel-burning appliance, or a fuel-burning fireplace, or have an attached garage, but are located in a building with a fuel-burning appliance, or a fuel-burning fireplace, or an attached garage, need not be provided with CO alarms provided that:

The sleeping unit or dwelling unit is not adjacent to any room that contains a fuel-burning appliance, a fuel-burning fireplace, or an attached garage; and

The sleeping unit or dwelling unit is not connected by duct work or ventilation shafts with a supply or return register in the same room to any room containing a fuel-burning appliance, a fuel-burning fireplace, or to an attached garage; and

The building has a common area CO alarm system.


Local code officials will check for compliance with the CO alarm installation requirements when a permit is required for new construction and most alterations, repairs or additions.

CO alarm installation requirements

1. Alarms must be located outside of each separate sleeping area, in the immediate vicinity of the bedroom and on each level of the residence.

2. Single station carbon monoxide alarms must be listed as complying with UL 2034, and installed in accordance with the code and the manufacturer’s instructions.

3. Combined CO and smoke alarms are permitted.

For more information

State Building Code Council staff can be reached at 360-407-9279

CO poisoning and prevention – the Department of Health CO web page.