Building Codes FAQs

The 2021 Building Codes will go into effect March 15, 2024.

Where do I find the changes to the code?

Click the links to be redirected to each code:

  • Residential Code with Washington Amendments > view
  • Residential Energy Code > view
  • Plumbing Code > view
  • Electrical Code > view
    • To go into effect April 1, 2024 per L&I


Looking for another code? click here

What are the significant code changes for the codes that went into effect March 15, 2024?

What resources are available to help me comply with the energy code?

WSU Energy has compiled a list of resources to help with compliance > click to be redirected

BIAW has assembled a worksheet as well to help you plan with costs in mind > view worksheet

Can you explain HB 1589?

Can I use natural gas under the new energy code?

It depends. Our state code HEAVILY disincentivizes natural gas use because it’s a fossil fuel.

If using natural gas, BIAW has found compliance is 3 TIMES more expensive than all-electric buildings, largely due to the amount of solar needed to offset disincentivization; even if your project doesn’t have ample opportunity for sunlight.

Can my HVAC contractor still sell me a natural gas furnace?

The new codes only apply to new HVAC systems that are included in new builds and/or replacements of HVAC equipment in existing homes that are being upsizing.

You may use natural gas if you’re renovating and/or doing an HVAC like-for-like system swap. This means you’re not able to increase the size of your existing natural gas furnace even if it doesn’t deliver enough heat for the square footage of your existing home.

Example: if you’re not satisfied with the level of heating produced by your current system so you want to upgrade to a more powerful unit, you would potentially have to utilize an electric alternative.

We are aware this is an interstate commerce issue. To raise the prominence of the issue, please contact your congressperson.

Options for Energy Code Compliance

BIAW has compiled the credit options, and required pairings of credits, for use by our members.

To view, click the “See the Board” button below.

Does BIAW offer any recommended pathways for compliance?

All information, content, and materials regarding pathways for energy code compliance are for general informational purposes only, and do not constitute a formal recommendation from the Building Industry Association of WA (BIAW). No reader or user of this information should act or refrain from acting on the basis of this information without consulting the appropriate professionals. All liability with respect to actions taken or not taken based on the information provided are hereby expressly disclaimed.


Medium Dwelling Unit = 8 credits needed

R406.2 Energy Equalization Credits
Ductless Mini-Split: Type 4 = 3 credits


R406.3 Energy Credits

  1. Option 1.2 = 1 credit
  2. Option 3.7 = 2 credits
  3. Option 5.6 = 2 credits

Do I have to use continuous insulation?

Yes, if you’re following the prescriptive requirements. However, if you opt to earn points in R406.3 (options 1.1 – 1.4) and meet or surpass the reduction percentages for total UA, there’s potential to forgo using continuous insulation. To use this option and prove the reduction, you will need to use the C3 calculator published by WSU Energy. Since 2009, the C3 calculator has been a state endorsed compliance tool.

Below is hierarchical code language illustrating the two options for builders/designers: prescriptive OR the Total UA Alternative. Pursuing the Total UA Alternative helps you achieve credits toward the overall required credit thresholds.

  1. Efficient Building Envelope Options – Only one option from Items 1.1 through 1.4 may be selected in this category.
  2. Compliance with the conductive UA targets is demonstrated using Section R402.1.5, Total UA alternative, where [1-(Proposed UA/Target UA)] > the required %UA reduction.
  3. 1.5 Total UA alternative.If the proposed building thermal envelope UA is less than or equal to the target UA, the building shall be considered in compliance with Table R402.1.2. The proposed UA shall be calculated in accordance with Equation 2. The target UA shall be calculated in accordance with Equation 1. U-factors shall be determined as specified in Section R402.1.6. In addition to UA compliance, the maximum fenestration U-factors of Section R402.5 shall be met.
  4. TABLE R402.1.2  Above-Grade Wall U-Factor – 0.056
  5. Option 1.2 Prescriptive compliance is based on Table R402.1.3 with the following modifications:
    Vertical fenestration U = 0.25
    Floor R-38
    Slab on grade R-10 perimeter and under entire slab
    Below grade slab R-10 perimeter and under entire slab
    Compliance based on Section R402.1.5: Reduce the Total conductive UA by 15%. 


Download the C3* Calculator and Permit Forms at this link

Please note: C3 requires Excel for Windows installed on your computer (not web-based) and is not available for Mac computers.

Disclaimer: Results from the C3 assume that all data is entered correctly and completely. Results do not constitute an official decision. Your analysis should be reviewed by your building official/authority having jurisdiction.

*C3 means code compliance calculator.

What's the status on the WUI code?

Once SB 6120 is signed by the governor, no statewide WUI codes will be implemented until DNR re-configures the WUI map based on wildfire risk.

*Please note: some local jurisdictions have already implemented the code. If you believe you’re building in a high-risk area, please consult with your local planning department.

When is my project vested?

The legislature has codified the vested rights doctrine as applied to:

  • Building permit applications (RCW 19.27.095):

    A valid and fully complete building permit application for a structure, that is permitted under the zoning or other land use control ordinances in effect on the date of the application shall be considered under the building permit ordinance in effect at the time of application, and the zoning or other land use control ordinances in effect on the date of application.

  • Subdivision applications (RCW 58.17.033):

    A proposed division of land, as defined in RCW 58.17.020, shall be considered under the subdivision or short subdivision ordinance, and zoning or other land use control ordinances, in effect on the land at the time a fully completed application for preliminary plat approval of the subdivision, or short plat approval of the short subdivision, has been submitted to the appropriate county, city, or town official.

  • Development agreements (RCW 36.70B.180):

    A development agreement and the development standards in the agreement govern during the term of the agreement, or for all or that part of the build-out period specified in the agreement, and may not be subject to an amendment to a zoning ordinance or development standard or regulation or a new zoning ordinance or development standard or regulation adopted after the effective date of the agreement.

Who should I ask regarding technical questions?

Your local building department should be your first-stop in navigating the new codes.

If your planning department hasn’t fully answered your question and/or they too have questions still, please direct those questions to