Top 10 Real Estate Trends | Washington’s House Bill 1110 “Missing Middle” Housing Legislation
Top 10 Real Estate Trends Series: 1 of 10
It’s been over five years since the onset of the COVID-19 pandemic and a rollercoaster of political and economic influences, Fed policies, social issues, demographic trends, and game-changing technological advancements that have led to the present market truths being digested by consumers, developers, and real estate brokers alike. At the midpoint of this decade, Realogics Sotheby’s International Realty (RSIR) explores the trendlines that continue to shape the market, starting with Washington’s House Bill 1110.
House Bill 1110 passed in 2023 and is the largest “upzone” in Washington history. The bill is effective as of July 1, 2025. This landmark “missing middle” housing reform requires larger cities to allow multi-unit dwellings in previously single-family zones. It directly impacts developers, homebuyers, and sellers, and the previous consumer dependency and demand for in-city, high-rise condominiums, particularly as Seattle and Bellevue pivot from high-rise core growth to broader community redevelopment. This legislative mandate has been a controversial topic for NIMBY’s (“not in my backyard”) homeowners resisting changes to their neighborhoods. However, land brokers and local builders rejoice in the opportunity to redevelop infill communities and bring a higher volume of affordable housing options in a much quicker capacity, versus the protracted process and litigious reality of building high-rise condominium towers. This timely supply spike will hopefully address the much-needed homeownership price points below the median home prices of $885,000 in King County (the region’s most expensive housing market). Currently, 58% of Seattle households are renters, in large part due to affordability and inventory options.
The HB 1110 Mandate
Tiered housing density:
Cities ≥75K (like Seattle/Bellevue) must allow 4 units per lot citywide, and 6 units within a quarter-mile of major transit or if at least two units are affordable.
Similarly, mid-sized cities (25-75K) must allow duplexes or fourplexes.
More housing types legalized: Duplexes, triplexes, fourplexes, sixplexes, townhomes, courtyard apartments, cottage housing, stacked flats.
Streamlined regulations: Reduced design review, relaxed parking minimums near transit, limits on restrictive development standards.
Cities had to adopt these changes by June 30, 2025, or default to the state model code, which is broadly viewed as more onerous (municipal governments are also not permitted to include developer-adverse policies that are intentional to deflect builder demand).
Benefits for Developers
Increased Density Leads to Better Land Economics
The ability to build 4-6 units per lot means higher revenue potential from small, infill sites.
Reduced parking requirements and simplified design reviews lower costs and speed projects.
Canadian tariffs on lumber are estimated to add an average of $14,000 per home in the US, so building more efficiently scaled houses and hitting lower price points will help with affordability even as inflation in construction persists.
Flexibility in Housing Products
Developers can pivot between townhomes, cottage courts, stacked flats, or small condo buildings based on market demand.
Near light rail or RapidRide, build up to 6 units—even if not providing full on-site affordability—boosting returns.
Bellevue and Redmond are actively embracing up-zoning, with Bellevue estimating 100,000 new units added via code amendments.
Effects on Buyers & Sellers
Sellers
Landowners gain more value: A single-family lot now worth 4-6 units is a major asset uplift.
More motivated to sell: Particularly owners of older homes on smaller lots that are now viable for redevelopment.
Buyers
More entry-level options: Missing-mid housing creates smaller, more affordable units (duplexes, townhomes, cottage homes) that cost less to build and buy than detached homes.
Better access to transit and walkable neighborhoods: Enhanced supply near transit means more choice where people want to live.
Condo-style ownership is on the rise: Shared-lot developments with deeded condos become more common. Buyers get private ownership with lower cost than detached homes.
Shifting Demand: High-Rise vs. Community Redevelopment
As zoning opens up:
The center of gravity shifts outward: Instead of only high-rise towers downtown within existing zoning, expect mid-rise and low-rise condominium clusters in established residential neighborhoods.
Neighborhood transformation: Popular areas throughout the Seattle/Bellevue metro area will see clusters of duplexes, fourplexes, and sixplexes replacing single homes, especially near rapid transit nodes.
Community-based development: Smaller-scale projects—often 4-6 units—allow developers to work block-by-block rather than needing large parcels, and typically, existing infrastructure such as residential services, schools, lifestyle attractions, and other cultural considerations are already present and scalable.
Improved affordability: More units and variety put downward pressure on sale prices and rents across neighborhoods, albeit the evolution will take years to manifest, given that sellers will need to make the land available.
Quicker construction and less risk: Builders are more apt to develop infill micro-housing communities, which will take 1-2 years for permitting, construction, and sellout instead of high-rise communities that are subject to 5-8 years of comparative exposure.
The Final Take: House Bill 1110 is a transformative zoning and builder incentive tool: by legalizing 4-6 units per lot and streamlining regulations, it empowers developers, broadens options for buyers and sellers, and shifts real estate momentum from dense towers downtown to human-scale, community-integrated housing across the region. As small condo-style developments and cottages proliferate in single-family areas, the Puget Sound will see a genuine renaissance in in-city living—more affordable, walkable, and diverse. The Puget Sound Regional Council estimates that the metro area currently lags by approximately 54,000 dwelling units behind where it should be based on monthly targets, and 810,000 new units are required by 2050, with a majority near transit. Achieving these aims means dramatically scaling up development, aligning local policies with the PSRC’s VISION 2050’s housing and equity framework.
Click Here to Watch RSIR President and CEO discuss insights into House Bill 1110 with Principal of Gardner Economics Matthew Gardner. ➡︎
Information was obtained from sources deemed reliable but cannot be guaranteed. Readers are encouraged to perform independent due diligence prior to relying on information contained herein.
Sources include:
Key insight: HB 1110 passed in 2023; effective July 2025; Bill requires 4 units per lot in large cities; 6 near transit or with affordability: Implementing HB 1110 – City of Seattle Washington House Bill 1110
Key insight: Legalizes missing middle housing types (duplexes, triplexes, sixplexes, etc.): Washington’s Middle Housing Bill – Overview – Summit Law
Key insight: Tiered density requirements for cities ≥75K and 25-75K: Washington HB 1110 “Middle Housing” Bill – CG Engineering
Key insight: Cities must adopt by June 30, 2025, or default to state model code: HB 1110 Implementation Guidance – WA Dept. of Commerce
Key insight: Bellevue goes beyond state minimum; allows sixplexes citywide: Bellevue Adopts Middle Housing Code – HB 1110 Compliance – The Urbanist
Key insight: Renton’s zoning updates allow 4-6 units per lot: HB 1110: Code Updates – City of Renton
Key insight: Bellevue FAQ: housing types and unit-lot subdivision ownership: Middle Housing FAQ – City of Bellevue
Key insight: Statewide coverage of bill passage: Bill to Legalize Duplexes, Fourplexes in Washington Advances – AP News