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Washington mechanical, plumbing, fuel gas & energy codes

The Washington State Building Code Council (SBCC) adopts and amends the statewide codes. The IMC, IFGC and UPC are named in state law (RCW 19.27). The 2021 codes are in force, and the 2024 codes are scheduled to take effect May 3, 2027.

Quick answer: Washington currently uses the 2021 IMC for mechanical work and the 2021 UPC for plumbing (see sources and dates below). A2L status: Allowed: SBCC A2L rules for the 2021 IMC (check current rule)

Adopted codes

Mechanical
2021
IMC
Adopted as
Chapter 51-52 WAC (WAC 51-52-003)
Effective
2024-03-15
Source
WAC 51-52-003
Last checked
2026-10-29 verified
Notes
The SBCC took final action on the 2024 IMC/IFGC on Oct 16, 2026, and it's scheduled to take effect May 3, 2027.
Plumbing
2021
UPC
Adopted as
Chapter 51-56 WAC (WAC 51-56-003)
Effective
2024-03-15
Source
WAC 51-56-003
Last checked
2026-10-29 verified
Notes
Washington uses the IAPMO Uniform Plumbing Code (chapters 12 and 14 not adopted). The 2024 UPC is scheduled for May 3, 2027.
Fuel Gas
2021
IFGC
Adopted as
IFGC as amended in WAC 51-52-21000 and following
Effective
2024-03-15
Source
Chapter 51-52 WAC (full text)
Last checked
2026-10-29 unverified
Notes
The IFGC is adopted and amended within chapter 51-52 WAC. LP-gas installations use NFPA 58-2020 and NFPA 54-2021. We haven't confirmed the IFGC edition in the rule text; 2021 is inferred from the IMC adoption.
Energy
Residential: 2021 WSEC; Commercial: 2021 WSEC
WSEC (IECC-equivalent or better)
Adopted as
Washington State Energy Code (state-written)
Effective
Res 2024-03-15; Com 2024-03-15
Source
U.S. DOE Building Energy Codes Program – Washington
Last checked
2026-10-29 verified
Notes
DOE rates it equivalent to the 2024 IECC / 90.1-2022. The 2024 energy code is on a separate SBCC schedule.

A2L refrigerants in Washington

SBCC has used emergency rules to update the 2021 IMC for A2Ls. The most recent one we found was filed Feb 24, 2026 and coordinates with ASHRAE 15/15.2-2022, ASHRAE 34-2022 and UL 60335-2-40. It requires A1 or A2L refrigerant in high-probability comfort equipment and covers detection and ventilation. Emergency rules expire unless refiled, and we haven't confirmed which rule is in force today. The 2024 IMC with A2L provisions takes effect May 3, 2027.

Source: https://lawfilesext.leg.wa.gov/law/wsr/2026/06/26-06-043.htm · Last checked 2026-10-29 unverified

How A2L rules work nationally

Local amendments & things to watch

  • 2024 codes: SBCC took final action on the 2024 IBC/IEBC, IRC, IMC/IFGC, IFC and UPC on Oct 16, 2026. The effective date is May 3, 2027. verified source
  • Seattle publishes its own interpretation on enforcing the A2L emergency rule. verified source