While everyone’s focused on zoning reform—Seattle and other Washington jurisdictions updating their comprehensive plans to comply with HB1110—there’s another regulatory barrier to housing that most people don’t know about: the building code.
Currently, one and two dwelling structures are regulated by the residential code (IRC – International Residential Code). Everything else, whether it’s a downtown high-rise with hundreds of units or a simple triplex, is regulated by the commercial code. This creates a significant mismatch: a fourplex faces the same regulatory burden as a skyscraper, adding unnecessary costs, complexity, and delays to these simple structures.
Four years of advocacy paying off
In February 2022, I made a code change proposal (with the help of the AIA Seattle Housing Advocacy Committee) to the State Building Code Council (SBCC)—the organization that develops and regulates our codes—to allow multiplexes in the residential code. While this proposal didn’t make it out of council, it gained the attention of Representative Duerr, who ultimately sponsored legislation requiring SBCC to develop a TAG (technical advisory group) to create a pathway for multiplexes up to 3 stories and 6 units to be regulated by the residential code.
This legislation passed, and I’ve been watching this TAG process as it developed the new code, occasionally offering public comment during the meetings. Another person heavily advocating for this change is urban planner Markus Johnson, who made a code change proposal of his own and has attended nearly every meeting.
Where we are now
I’m excited to say that the Multiplex and Single Stair TAG has completed their work and passed draft code out of their committee. (The “single stair” component addresses exit requirements—another simplification for smaller buildings.) It also just passed out of the BFRW committee to go to the full building code council. This is real progress.
Beyond the building code itself, last summer I made a companion proposal in the Residential Energy Code TAG to allow these same multiplex structures—six units and three stories—to have the option to use either the residential energy code or commercial energy code for their design. This passed out of committee as well, creating consistency across both the building and energy codes.
Your chance to weigh in:
Public comment period: May 6 – June 12, 2026 ( I will post updates as links and information become available)
The state implementation of the 2024 IRC happens May 3, 2027.
I’m excited to see these changes happening to simplify the process of building housing in our state! It’s a positive step forward that could make it meaningfully easier and more affordable to build the “missing middle” housing our communities need. Here is a VOX article that sums up much of the issue.
