WA House Bill 1110 - Redesigning Washington’s Middle Housing Options

WA House Bill 1110 - Redesigning Washington’s Middle Housing Options

Washington state has been grappling with a surge in housing demand due to the influx of tech industry professionals flocking to the greater Seattle area. Unfortunately, this surge has coincided with a sharp decline in the number of available homes. As a result, home prices have soared to unprecedented levels, amplifying the issue of homelessness and displacement in Seattle. Recognizing the gravity of the situation, our state government has finally acknowledged the need to incentivize and enable investors to construct more housing options. This is where House Bill 1110 comes into play.

On May 8, 2023, Governor Jay Inslee took a decisive step by signing House Bill 1110 into law. This groundbreaking legislation allows for the construction of higher density housing in existing residential areas. Duplexes, triplexes, fourplexes, and in some cases, even six-plexes will now be permitted, presenting a significant departure from the traditional single-family home zoning.

By expanding the housing options available in established neighborhoods, House Bill 1110 aims to alleviate the strain on the housing market and create more affordable living spaces. This move represents a crucial shift in our approach to urban development, as it encourages denser housing arrangements that can accommodate a larger number of residents.

Understanding the Bill

Let's dive into the details of HB 1110 and the impact it will have on our neighborhoods. It is estimated that across Washington state an estimated 1,000,000 units will have to be built in the next 20 years to keep up with population growth and fix the housing crisis the state faces. To help alleviate this, HB 1110 will help us get closer to that daunting number by allowing for multi-family buildings to be built in single family neighborhoods. In most cases duplexes will be allowed on any single family lot, with some lots allowing building up to a six-plex. Here is a breakdown of the numbers:

  • Cities with populations between 25,000 and 75,000: 
    • Duplexes will be allowed on any residential lot. 
    • Fourplexes will be allowed if the project is located within a quarter mile of a transit stop, or if one unit is built as affordable housing.
  • Cities with populations over 75,000:
    • Fourplexes will be allowed on any residential lot.
    • Sixplexes will be allowed if the project is located within a quarter mile of a transit stop, or if at least two units are built as affordable housing.
  • Cities with a population of less than 25,000 that are located in an Urban Growth Area (See list of UGAs here) will also allow for duplexes on any residential lot.


What qualifies as a transit stop? These are stops on a high capacity transit system funded by Sound transit, a commuter rail stop, a rapid bus stop, or any stop considered to be a major transit stop by the Puget Sound Regional Council.

In order for a unit to be considered affordable housing the units must be maintained as affordable housing for 50 years and the property has to satisfy the local jurisdictions affordability and income eligibility requirements. The city will record a covenant or deed restriction that will ensure that the units continue to be a part of the affordable housing program for at least 50 years. The units that are affordable units must be similar sizes to the other units in the project with similar proportions of bedroom and bathroom counts. This means you can't build the affordable units to be drastically different from the remaining units in the project.

The bill also streamlines the design review process requiring only administrative design review. Cities must treat these middle housing options the same as single family projects in the design review process which accounts for factors such as setbacks, lot coverage, stormwater, tree canopy, and retention requirements. 

The bill also discusses parking requirements. A city shall not require more than the following off-street parking guidelines:

  • Lots located within ½ mile walking distance of a major transit stop: no off-street parking requirement.
  • Lots smaller than 6,000 square feet: one off-street parking space per unit. 
  • Lots larger than 6,000 square feet: two off-street parking spaces per unit. 

The bill does not apply to homes within a one mile radius of a major airport, or any lots that are located within a critical area. 

When will this go into effect?

The bill was passed on April 18, 2023 and the effective date of the bill is  July 23, 2023. The bill requires that a city or county adopt the bill within six (6) months after the jurisdictions next periodic comprehensive plan update if the city meets the population threshold based on the 2020 population data, or twelve (12) months after the next implementation progress report if the city reaches the population threshold. The next planned comprehensive plan updates are as follows (view webpage):

  • King, Pierce, Snohomish, and Kitsap Counties: December 31, 2024
  • Whatcom, Skagit, San Juan, Island, Clallam, Jefferson, Mason, Thurston, Lewis, and Clark Counties: June 30, 2025

That means that the very latest we would see this bill take effect would be May 31. 2025 for King, Pierce, Snohomish, and Kitsap Counties, however it is possible that the bill will be adopted before the next plan update. 

What does this mean for you?

So, what does this mean for you? If you're a homeowner, this bill allows for much more flexibility in building extra units for rental income or affordable housing for family members. By legalizing more options in residential neighborhoods the bill helps provide a solution to the major housing crisis our state is facing. More middle housing options means more affordable choices near jobs, schools, and transit. By increasing the density in existing residential neighborhoods, we can preserve more of our farmland and forests while also increasing the walkability of our communities. Washington has about 1.8 million detached homes that occupy nearly 75% of the state’s residential land. With this bill, even if only a fraction of those lots gain new homes, thousands of units will be built helping with our housing crisis. 

If you’re an investor, this is a huge opportunity to build additional units on existing single family lots, helping you maximize the potential of existing residential lots. Overall, this bill will help all Washingtonians to increase the density of housing on existing lots and provide massive amounts of equity for existing homeowners. 

Written by: 

Rebecca Bridges & Michael Haas. Michael Haas is a Managing Broker & leads the team of Investor-Agents at HouseHack Seattle. He has built multiple DADU’s and ADU’s & new construction homes- you can schedule time with him here to talk about this & other Investing & HouseHacking strategies: https://calendly.com/michaeljohaas/30-min-meet 


We've helped clients build portfolios of gorgeous Airbnb Cabins, become rental property owners and landlords, and use down-payment assistance programs and House-Hacking to afford a better home than they had dreamed was possible. I’d love to hear a bit more about your investment goals, and chat about how I might be able to help.

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