Washington State Energy Code 2021 (WSEC)

The state of Washington recently wrapped up a lengthy residential energy code update process. The new energy code, Washington State Energy Code 2021, has many updates that will, over time, give builders more code compliance options and better align the code compliance process with valuable Federal Energy Efficient Construction Tax Credits.

This blog will explain the history of code compliance software and describe the key aspects and changes to each compliance pathway. This blog is based on the energy code as published on February 21, 2024 (this article will be updated as new information becomes available). 

History of the code compliance software

Washington State has historically had a heavily amended version of the IECC energy code. This made it difficult for code compliance software providers to support the performance pathway of the Washington State Energy Code and it remained unsupported. Consequently, this meant that residential code compliance was shown using the Total UA or Prescriptive pathway. To support those pathways, the Washington State University Energy Program has built numerous tools and calculators to help calculate compliance. These tools were necessary due to the uniqueness of the energy code and the lack of market-based software solutions. 

In 2022, Washington State began a code revision process that included a ban on new natural gas hookups. This code revision process has been heavily delayed for numerous reasons. The code is slated to be effective as of March 15, 2024 (There is currently a request to stay the implementation of this new code in front of a court), and yet the code may still have revisions. The delays stem from litigation initiated by industry stakeholders seeking to prevent the fossil fuel ban and the remaining uncertainty around the code requirements. As written, the new code does not mandate all-electric homes and instead provides incentives for all-electric homes. It also creates a viable Performance Pathway that creates synergies with the 45L Federal Tax Credit. 

What is the new code:

The new Washington State Energy Code (WSEC) is based on the IECC 2021 energy code with some major revisions. I will call it WSEC 2021 moving forward. It can be found here. As new versions are released, this blog will be updated. This code applies to all “one- and two-family dwellings, Townhouses and R-3 (2 dwelling units or less) buildings three stories or less, and Group R-2 (multifamily) buildings that are three stories or less with dwelling units that are accessed directly from the exterior.”

There are three compliance pathways in the WSEC 2021. A home must comply with one of the following. 

Option 1: R401-404 Prescriptive and R406 Additional Credits

The prescriptive pathway requires compliance with sections R401, R402, R403, R404, and R406. Within R402 is both the prescriptive checklist for all building envelope specifications and a Total UA alternative compliance pathway. Buildings may either utilize the Total UA alternative or component-by-component checklist requirements. The WSU Energy Program builds tools to assist in calculating compliance for these two options.

In addition to meeting these requirements, homes must also comply with Section R406. This section creates a point-based system that encourages electrification. This score sheet is only required for the prescriptive compliance pathway. The section requires different building types to achieve a specific point total for compliance. A few examples of ways to score points are: 

• 2 points for having a ductless mini-split heat pump 

• 1.5 points for enhanced total UA

• 1 point for enhanced building envelope leakage 

The specific point requirements vary for different types of buildings. The categories are small, medium, and large dwelling units, R-2 dwelling units, and additions (see below). 

Option 2: R405 Total Building Performance 

Ekotrope currently supports this code compliance pathway. 

The WSEC 2021 R405 pathway is similar to the standard IECC 2021 in methodology and process. Importantly, and a significant change from past versions of the WSEC, R406 is not required. This removes a major barrier to pursuing the performance pathway. 

The most notable changes to the WSEC 2021 compared to IECC 2021 are the elimination of a building thermal envelope backstop, alteration of the reference home specifications, and the change in compliance metrics. 

The WSEC 2021 does not have the IECC 2009 thermal backstop as the standard IECC 2021 does. In the standard IECC, a home has the flexibility to select any U-value assemblies for the thermal boundary as long as it is more efficient than a backstop - in the IECC 2021 that backstop is the IECC 2009 U-value minimums. The WSEC has removed this requirement giving more flexibility.

The performance pathway compares the as-built home’s modeled energy performance against a reference home's modeled energy performance. The WSEC 2021 has made one key edit to the reference home’s thermal boundary specification. The standard IECC 2021 energy code’s reference home utilizes an approximately R-21 wall assembly. The WSEC 2021 has reduced the reference home’s exterior wall R-value to about R-19 (see Table R402.1.2 below) - again making it a bit more flexible. 

The WSEC 2021 has building type-specific compliance metrics. The building types are the same as listed in the prescriptive code (e.g., small, medium, large buildings, …). In the IECC 2021, compliance thresholds do not depend on these building type categories. 

Additionally, the WSEC changes the metric of compliance from utility cost to site energy consumption. WSEC says that for each building type, the proposed home must have the site energy consumption be 41-64% less than the standard reference home. In the standard IECC 2021, homes must only perform better than the standard reference home (this means a minimum >0% reduction in energy usage). The full chart is below:

Option 3: R407 Passive House

The final compliance pathway is through the PHIUS or PHI versions of Passive House certifications. The respective requirements are for PHIUS to comply with PHIUS+ 2019 Passive Building Standard and for PHI to comply with Low Energy Building Standard, version 9f or later. For both programs, an official project certification must be earned and presented to the building official to receive a certificate of occupancy. 

What is the C3 calculator?

The Code Compliance Calculator (C3) tool was developed by the Washington State University extension to assist builders and code officials. It helps them show compliance with the WSEC 2021 via the Prescriptive and Total UA Alternative compliance pathways (Option 1).  It is not required for homes that are showing compliance via section R405 or R407 or if using an alternative Total UA Alternative compliance tool. 

What does my code official need to see to approve an Ekotrope report showing compliance with the WSEC 2021 Performance Pathway?

Compliance with the WSEC 2021 Performance Pathway is shown by producing a compliance report that includes standard information regarding the home's location, who completed the analysis and generated the report, the software used, an energy analysis report showing compliance status, and the building component summary. 

The code official may require documentation that the software used performance calculations following the energy code. Unfortunately, there is no governing body that evaluates and approves software for code compliance use - it is left up to each code official to determine. In these cases, Ekotrope has had success showing compliance to code officials via letters of attestation and utilizing the building summary report. 

Table R-402.1.2 is referenced as the primary source of reference home envelope behavior and component U-Factors.