March 25, 2024

Washington State Energy Code Updates: What to Know


The final version of the 2021 Washington State Energy Code (WSEC) went into effect on March 15, 2024. The updated residential energy code includes new requirements and more options for earning credits, which will enhance the energy efficiency of high-performance residential construction, and contribute to the health and comfort of homeowners. BetterBuiltNW analyzed the state energy code and prepared a breakdown of the most noteworthy changes.

Revised space and water heating fuel requirements between draft and final 2021 WSEC

Changes from the draft to the final 2021 WSEC include removing the heat pump requirement for space and water heating, and changes to the additional efficiency credits.


Draft 2021 WSEC

Final 2021 WSEC

Required heat pump (electric or gas) for space and water heating, with some exceptions

Allows the same space and water heating equipment as 2018 WSEC


Updates to Section R406: Additional Energy Efficiency Requirements

Each new single-family home built in Washington requires minimum energy credits beyond the prescriptive minimums based on its size (Section R406.3). All three home size categories now require more credits and the code is more stringent than the original draft of the 2021 WSEC. For a small home (<1,500 square feet) a builder needs to comply with five credits, a medium home (1,500–5,000 square feet) needs eight credits, and a large home (>5,000 square feet) needs nine credits. Homes with combustible fuels, like natural gas, must obtain more energy credits than homes using electric heat pumps for space heating.

In the final 2021 WSEC, there are now 29 different energy credits across seven categories (Table R406.3). Here are some details about the changes for additional energy efficiency requirements:

  • Table R406.2: Energy equalization credits
    • A builder is given a number of credits based on the fuel type for space heating. There are five heating system types, and credits range from zero for combustible fuels to three for a heating system using an efficient electric heat pump.
  • Table R406.3: Energy Credits
    • New high-efficiency gas space and water heating credits options were added. Options for high efficiency combustible fuels either as primary or as a backup are available and two options exist for high efficiency combustible fuels in water heating.
    • Envelope credit option values were increased to reflect the most up-to-date envelope and HVAC requirements.
  • Net impact considerations
    • Compared to the 2018 WSEC, the final 2021 WSEC is more efficient for all fuel types. Although combustible fuel types are an option for space and water heating, using natural gas requires more efficiency credits than using electric heat pumps for the same purposes.

Electric space and water heating is the easier pathway for compliance, in terms of the number of credits required and credits available for selection. However, builders should analyze the choices and tradeoffs in each category for credits, as well as the fuel types that can be used. The code has many options with the intent to create as much flexibility as possible, while still building high performing homes.

A clear understanding of code changes will make adapting easier

The final 2021 WSEC isn’t drastically different from what you’re already used to, but the changes outlined above could impact your building practices. Working with a Rater or verifier can help ensure your upcoming projects meet and potentially exceed code to qualify for energy efficiency certification and incentive programs.

Watch this training from Washington State University (WSU) for an in-depth look at the details of the 2021 WSEC. For further assistance on the new code, explore other building efficiency resources from WSU's Energy Program or reach out to the BetterBuiltNW team.

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