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Washington · RCW 19.27.530Washington carbon monoxide alarms: the seller's duty before the buyer moves in

Washington requires carbon monoxide alarms in buildings classified as residential occupancies under the state building code. Owner-occupied single-family homes legally occupied before July 26, 2009 are exempt – but when such a home is sold on or after that date, the seller must equip it with carbon monoxide alarms in accordance with the state building code before the buyer or anyone else may legally occupy it after the sale (RCW 19.27.530(2)(b)). In a rented building, maintaining the alarm, including replacing batteries, is the tenant's responsibility under the rules the building code council adopts (RCW 19.27.530(4)). Real estate brokers licensed under chapter 18.85 RCW aren't liable in any civil, administrative or other proceeding for a seller's or owner's failure to comply (RCW 19.27.530(5)).

The rules

  1. 1. Seller equips (RCW 19.27.530(2)(b))

    CO alarms per the state building code before the buyer may occupy.

  2. 2. Which homes

    Owner-occupied single-family homes sold on or after July 26, 2009.

  3. 3. Rentals (RCW 19.27.530(4))

    The tenant maintains the alarm and replaces batteries.

  4. 4. Brokers (RCW 19.27.530(5))

    Not liable for a seller's failure to comply.

What the TC can do

  • Remind the seller early that CO alarms have to be in before the buyer moves in.
  • Ask the buyer's agent to check for the alarms at the final walkthrough.
  • Note the seller's confirmation in the file.

Questions about Washington CO alarms

Does a Washington seller have to install carbon monoxide alarms?

Yes – for an owner-occupied single-family home sold on or after July 26, 2009, before the buyer may legally occupy it (RCW 19.27.530(2)(b)).

Is a Washington broker liable if the seller doesn't install CO alarms?

No – licensed brokers aren't liable for a seller's failure to comply (RCW 19.27.530(5)).

Related guides

Add a task in ClosingCode for the seller's CO alarms before move-in, with an owner and a due date.

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Source: Revised Code of Washington 19.27.530 (app.leg.wa.gov, read October 26, 2026).

General information, not legal advice. The alarm type and placement follow the state building code. ClosingCode is software; it is not a law firm. This guide is not a substitute for the advice or services of an attorney.