Update: Seattle City Council will host a Public Meeting to discuss Council proposed addenda to the Phase 1 legislation on September 12, 2025.

With the city continuing to face a historic housing shortage, Seattle’s upcoming Comprehensive Plan update intends to enact the updates required by the state of Washington’s HB 1110 as a way to bring relief to this issue, by creating more opportunity for diverse housing options in the Neighborhood Residential zones. Central to this effort is an allowance of development of "missing middle housing," a term that encompasses a range of low-rise multi-family housing types including duplexes, triplexes, townhomes, courtyard apartments, and small-scale stacked flats. While the effort is significant, the city of Seattle’s Design Review process, coupled with permitting unpredictability, and existing zoning constraints in other zones pose significant hurdles fully diversifying housing types or creating affordability in the market.

Current Landscape: Single Family Developments including Attached and Detached Accessory Dwelling Units Dominate

In the last few years, residential development in Seattle has transitioned from townhouse projects to Single Family developments that include attached Accessory Dwelling Units (ADUs), and detached accessory dwelling units (DADUs). Prior to June 30, 2025 lots zoned Neighborhood Residential in Seattle allowed one principal Single Family residence, one ADU and an additional ADU or one DADU. Since these projects are located in the Neighborhood Residential zones which do not require Seattle’s Design Review process or Seattle’s Mandatory Housing Affordability program, builder developers have been focused on  these projects as they save time and money and are more predictable. This trend reflects the limitations imposed by zoning laws that favor single-family and low-density housing, coupled with the high costs and risks associated with multi-family development.

A survey of our completed projects confirms how important alley access is to this small-scale infill housing typology. Vehicles are limited to the rear of the lot, allowing the rest of the site to prioritize the residents. This allows for the creation of a central courtyard as a shared outdoor space for residents. Such spaces can foster community interactions and improve the quality of life for residents. Unfortunately, due to Seattle's platting history, there are a large number of lots without access to alleys, limiting the potential for this type of redevelopment.

While ADU and DADU developments offer some relief from the city’s housing crisis, they fall short of meeting the massive demand for affordable and varied housing. While some affordability is gained due to the limited size of ADU and DADU’s (1,000 sq ft of interior space), these projects often cater to moderate- to high-income households, without families, leaving low-income renters, or families with few options. The city’s Comprehensive Plan seeks to address these gaps by fostering the development of a wider variety of housing types, some of which are currently underrepresented in Seattle’s housing stock.

A Single DADU, behind a home in the Central Area. Before the change in owner occupancy requirements, this type of project was rare in Seattle.

A diagram showing a two neighboring Single Family, ADU and DADU projects. After legislation changed allowing owners to rent all ADUs, DADUs and Single Family homes on a site and developers selling them through a type of condominium, this project type started replacing townhomes as the popular development solution. This is also due to a lack of design review requirements and mandatory housing affordability in this project type.

A street facing render of two Single Family and attached ADUs. This is the type of project preferred in 2023-mid 2025.

Barriers to Urban Missing Middle Housing

Seattle’s Design Review process provides a key challenge to developing middle housing in Seattle, which adds significant time and cost to projects as well as a great deal of unpredictability. This process emphasizes exterior design and neighborhood input over housing variety, affordability or permitting efficiency. The process encourages material quality and exterior design principles, much of which is already desired by architects and developers. This  process offers no support for developers pursuing small to medium multifamily projects. Such projects require the same amount of oversight as large multifamily projects, but with less potential revenue, often making smaller rental buildings financially infeasible. While projects that commit to 75 years of affordable housing can avoid design review altogether, the strategy is less viable for smaller rental projects like infill apartments or stacked flats.

Parking also plays a significant role in shaping the city’s housing landscape. While the comprehensive plan aims to encourage transit-oriented development, safe street access, proper turn around space for vehicles will often monopolize the ground plane of small to medium scale projects. This allocation of space for cars will either lessen unit counts or amenity space or both, further decreasing the quality and value of smaller projects. 

Additionally, the risks associated with condominium construction - including liability and financing issues - continue to disincentivize developers from prioritizing building for sale stacked flats, courtyard apartments, or infill condominiums. These housing types, which could significantly increase density and affordability, remain a less attractive option for many developers due to the increased risk.

A 13-Unit infill apartment in Wallingford. Canceled and became a townhouse project due to financial barriers and its small size.

A 14-unit infill apartment in Yesler Terrace. Canceled and became townhouses due to financial barriers.

A diagram of Ship Street. An infill apartment designed and built between 2015-2017. The price of construction, land and increased interest rates, make this solution harder to pencil today, although we do have two under construction right now.

Ship Street’s finished outdoor lobby and courtyard.

The Need for Diversity of Housing Solutions

On June 30, 2025, Seattle adopted interim legislation that allows 4 principal dwellings on all Neighborhood Residential lots and 6 units depending on access to “major transit” stops and projects that provide affordable housing. This significant change is in response to Washington States House Bill 1110, mandating the inclusion of Missing Middle housing, which includes more multi-unit dwellings like duplexes, triplexes, apartments and townhouses in areas historically zoned for single-family homes. This legislation is designed to address Washington State’s housing shortage and affordability crisis by providing more options between large apartment complexes and single-family houses.

One potential solution for diversifying housing types in the missing middle is unlocking the potential of smaller infill single-lot developments. As the comprehensive plan takes effect, opening Neighborhood Residential zoned lots to greater density and increased housing options, the new code will create flexibility for more units on each site and reduce parking requirements. Unfortunately condominium laws will continue to disincentivize small scale for sale stacked housing. A new law in Washington state exempts two-story condominium buildings with 12 units or less from compliance with state requirements; however, other regulations will prioritize structures that are three stories, making this infeasible in Seattle.  Other projects consisting of small multi-plex buildings on individual lots can increase density without drastically altering neighborhood character. Building Code reform can make these small mulit-plex structures more feasible, however, current building code requirements for these structures add cost and complexity, resulting in the production of mostly detached homes and  townhomes, which are more profitable but offer fewer units and less housing diversity.

Additionally, the scope of Design Review in the new comprehensive plan is not fully understood. The Mayor’s office has proposed reform to Design Review due to, as of June 30, 2025, the City’s Design Review Program is not compliant with recent changes to State Law (SB 1293). Seattle City Council will soon be considering interim legislation that will temporarily suspend required Design Review, making Design Review voluntary. This interim legislation will be in place while SDCI works to develop permanent changes to the Design Review program and guidelines. Projects which have a Design Review component may choose to withdraw from the program or to continue with voluntary Design Review. Ideally, major changes will be adopted to the current requirements of Seattle’s Design Review program in order to comply with State Law and support the production of a variety of housing types throughout the newly opened Neighborhood Residential zone and the rest of the city’s land previously responsible for housing production.

In our 20+ years at b9 architects, we have successfully completed many infill small to medium scaled multifamily apartment projects. These developments demonstrate the potential of this housing type to provide compact, efficient, and community-oriented living spaces. Unfortunately, we’ve also encountered multiple smaller scaled multifamily apartment projects that could not be realized due to regulatory and financial constraints. Addressing these barriers is crucial to unlocking the full potential of single-lot apartments as a missing middle solution.

A townhouse project on Sand Point, an excellent example of the potential of Missing Middle Housing. (View from the West)

Sand Point Townhouses viewed from the East.

This rowhouse in Ballard was added as part of a project that maintained two existing single family houses, and added a new Single Family home and duplex behind the rowhouse. Developing multiple sites and flexibility allowed for multifamily project with several missing middle strategies included.

The courtyard of Urban Canyon is a great example of the kind of communal spaces that can be realized with the correct site conditions.

Short-Term Affordability Concerns

Despite the promise of missing middle housing, the proposed changes in the comprehensive plan are unlikely to impact short-term affordability. Many of the missing middle solutions being incentivized involve replacing a single-family house, often valued around $700,000, with 4-6 townhomes. However, these new townhomes are frequently priced over $1 million each, reflecting the high costs of land, construction, and market demand. As a result, these developments may not address the immediate needs of low- or middle-income residents, potentially furthering affordability challenges in the short term.

What the Comprehensive Plan Should Achieve

If implemented effectively, Seattle’s Comprehensive Plan should:

1. Rezone Single-Family Areas: By rezoning single-family neighborhoods to allow duplexes, triplexes, and other multi-family housing types, the city can create opportunities for more diverse and affordable housing options.

2. Streamline or Eliminate the Design Review Process: Simplifying the process or exempting projects from the Design Review process will reduce costs and accelerate development timelines.

3. Reduce Parking Requirements: Eliminating or minimizing parking mandates  would free up space for housing and reduce construction costs.

4. Incentivize Innovative Housing Types: Providing financial or regulatory incentives for developers willing to innovate with urban missing middle typologies, such as stacked flats, courtyard townhomes, or single-lot apartments, would help bridge the gap between single-family and high-density housing.

The Path Forward

Seattle’s Comprehensive Plan update represents a crucial step toward addressing the city’s housing crisis. However, achieving the plan’s goals will require more than policy changes, it will demand a cultural shift in how the city and its residents view density, affordability, and community. Developers, architects, and policymakers must work collaboratively to create housing solutions that balance efficiency, affordability, and quality of life.

By embracing the potential of missing middle housing and addressing the barriers that have stifled its growth, Seattle can pave the way for a more inclusive and sustainable future. The Comprehensive Plan’s success will ultimately depend on the city’s ability to turn vision into action, ensuring that all Seattleites have access to the housing they need.

The 5th Avenue Townhouses used an alley to put parking access to the rear of the site and open a shared courtyard.

The Galer Rowhouses, on Queen Anne Hill, provides a strong connection between all units and the sidewalk through front stoops.

Row 1412 is an Urban+ project that retained an existing Single Family house while adding a duplex and a rowhouse around the project sites. The rowhouse is oriented to engage the street directly with backyards connecting to a common shared walkway and courtyard.

Our Principal, Brad Khouri, has been appointed Affiliate Assistant Professor at the University of Washington's Department of Architecture for the 2025–2026 academic year. This appointment recognizes his over two decades of dedication to architectural education and his significant contributions to urban housing design.​

Since 2003, Brad has served as a part-time lecturer at UW, teaching a diverse range of studios across undergraduate, graduate, and thesis levels. His courses often focus on the intersection of design innovation, policy, sustainability, and residential development, reflecting his professional expertise in infill urban housing. Notably, he co-led a research studio investigating housing density and equity, where students collaborated on design projects in specific Seattle neighborhoods.

In his new role, Brad will continue to teach the Housing Studio in Fall 2025, guiding students through the complexities of multifamily urban housing design. His ongoing involvement in both academia and professional practice ensures that students benefit from real-world insights and contemporary design challenges.

Samples of the work generated by the students of the 2024/2025 Architecture 503 Studio

b9 Architects is thrilled to announce the well-deserved promotion of Megan Zeien-Perez from Project Designer to Associate. Megan, who joined the firm on December 30, 2019, has consistently demonstrated outstanding dedication, creativity, and leadership in her role.

Megan has been an integral part of the b9 architects team, contributing her skills and expertise to a diverse range of projects, including townhouses, small apartments and our nearly completed 107-unit Passive House certified apartment. Her commitment to excellence, innovative design solutions, and willingness to engage in all aspects of company leadership has set a high standard for the firm.

In her new role as Associate, Megan will be taking on expanded responsibilities, with a focus on championing b9 architects' design standards and brand. Her passion for architecture aligns seamlessly with our commitment to creating site specific, forward thinking design solutions.

Megan's dedication extends beyond her design work, as she regularly seeks out new challenges in non-billable aspects of the firm, including business development. She assists new clients in project feasibility, helping b9 forge meaningful partnerships, and contributes to the firm's growth and success. Her growth mindset makes her an ideal candidate for leadership opportunities.

Additionally, Megan has been playing a key role in the onboarding of new employees, leveraging her experience to ensure a smooth integration of fresh talent into the b9 architects team.

"We are thrilled to recognize Megan's exceptional contributions to b9 architects with this well-deserved promotion to Associate in recognition of her passion for design excellence, commitment to the health of the organization, and enthusiasm for fostering connections with clients and team members" said Bradley Khouri, Principal at b9 architects.

Megan Zeien-Perez's promotion reflects b9 architects' commitment to recognizing and nurturing talent within the organization. As we look to the future, Megan's leadership will play a pivotal role in driving the continued success and growth of b9 architects.

selected works

Ballard Townhouses

Graceland Apartment

Madrone Passive House

Midvale Apartment

Urban Link

Ballard Apartment

Lee Townhouses

Market Townhouses

Aloha Duplex

As part of its plan to increase housing options in the city and to find solutions to solve missing middle housing, the City of Seattle has recently changed regulations around accessory dwelling units. Commonly referred to as a mother-in-law apartment,  an accessory dwelling unit is a smaller residential unit tied to a single family house that comes in both an attached and detached typology, known as ADU and DADU respectively. Picture a finished basement with its own kitchen and entry from the rear or a separate cottage on the same property.

In previous years, the Seattle Municipal Code enforced by the Seattle Department of Construction & Inspections (SDCI), required two significant items that dramatically reduced the feasibility of ADU or DADU projects. One, each ADU required onsite parking be provided, and two, the property owner would have been required to physically reside in one of the units on the site for at least 6 months out of the year.  In addition the units were limited to 800 square feet. The former requirement ate up valuable footprint space making a lot of Seattle sites, especially those with environmentally critical areas like slopes and wetlands, too small to add an additional structure, and the latter often priced out any developer beyond a homeowner interested in taking on construction risk to invest in their property. In 2019, the City of Seattle removed these requirements and began allowing two ADU’s per lot. Since then Seattle has seen an increase in this type of project entering the permitting process.

While this change definitely encouraged the development market to explore another avenue to create housing, the ADU/DADU cluster has very little difference to a project type we at b9 architects are already familiar with; namely, the duplex and Single Family house, or even a three unit townhouse development. Where the two differ most is in zoning and size.

As a part of the change to the municipal code that allowed this type of project to flourish, the City has made this three unit typology admissible in all Neighborhood Residential zones (formerly Single family residential), a zone that until this change could only allow one house with one accessory dwelling unit. With this change, a significant portion of land in the City of Seattle has been unlocked as developable. The trade off is in size. While Seattle’s multi-family zones would allow three townhouses of any size (so long as they meet FAR guidelines) this typology limits an ADU or DADU to no more than 1,000 sq ft each, with allowances for storage and garages that exceed that amount. 

The 335 DADU is a small backyard residential unit completed in 2017. This would have been the only typology allowed in Single Family zones.

The 335 DADU is a small backyard residential unit completed in 2017. This would have been the only typology allowed in Single Family zones.

If you look at our 2018 study Urban +, you’ll see how the backyard building can range in size and scale based on the lot number, size and zone. In 2018, the only thing that could be done with a single lot in the Single Family zone is what you can see in our 335 DADU project. Since the code changes, the new type of project could resemble the configuration of several of our completed projects, including Urban +, Urban Share, or the North lot in Row 1412. In 2022 we used our expertise in Urban + to help two of our clients approach this type of project.

An axon of the 335 DADU. This project could add an additional ADU based on new requirements.

An axon of the Judkin’s Park House. This configuration would not be allowed in Neighborhood Residential zoning due to the location and size of the two homes.

An axon of the Urban Share project. While it’s three units, this configuration would not be allowed in Neighborhood Residential zoning due to the location and size of the two homes.

The Genesee ADU Cluster in West Seattle will add five residential units across two sites of current single family homes. One of these primary residences will be retained and converted to the allowable DADU for that lot. The other existing residence will be removed to make room for the new dwellings. The duplexes (or Single Family w/ ADU) that face the two streets are three stories with living on the second floor. Each new unit has at least two bedrooms, with the two larger units designated as Single Family Houses having three bedrooms. Similarly, in our project Urban Share, a Single Family home remained on site while a duplex was built behind it. If Urban Share were on a Neighborhood Residential zoned lot today, the two small units in the duplex would be comparable in size to what is allowed now as an ADU or DADU.

The Genesee ADU Cluster retained an existing Single Family House.

Due to being a corner site with access to two streets, we are position the existing Single Family house behind a new structure, and designate it as the site’s DADU.

The site plan for the Maple Leaf ADU Cluster is organized to give each of the three units a private outdoor space. While each of these spaces is accessible to all three units, they are recessed from the street and are configured like a checkerboard with each unit exiting through a rear door onto an established space. Due to the new code allowances, parking is only provided for the front Single Family home in a ground floor garage.

In the end, the driving factor for the large increase in ADU and DADU development in Seattle is cost, specifically related to the process required to obtain a permit for construction. These three unit projects, while being similar to a three unit townhouse project, are not required to participate in the city’s Design Review program, or comply with the requirements of the Mandatory Housing Affordability program. This streamlines the entitlement process, and saves money while being more predictable. While this will help bring the much needed residential units to the area, it will increase the amount of small ADU and DADU units that come to the city, which offers a more affordable option in the market.

Happy New Year! At b9 architects, we have the good fortune of having a large portfolio of completed works. Due to the diligence and expertise of our clients, the majority of the residential projects we’ve designed are completed, a feat not all architecture firms have. In 2022, we examined a couple projects that, due to the economic realities of Seattle, were canceled mid-process. Due to the increasing costs of construction, longer permit entitlement processes, and current incentivisation programs in the municipal code - creating dense, rentable residential units is not always cost effective, especially on small or complicated sites. Here are case studies of two projects that did not move forward.

Midvale Apartment

The Midvale Apartment Building and its surrounding neighborhood were up zoned when the City of Seattle implemented the Mandatory Housing Affordability (MHA) legislation in 2019. Properties facing the main arterial, Stone Way, remained in the Neighborhood Commercial zone but received a height and allowable area increase.  The neighborhood to the west was largely shifted from the exclusive Single Family zone to the more flexible Residential Small Lot zone. Our site, however, and everything on the half block between the two received the intermediate Lowrise Multi-Family designation. 

As a potential transitional space between the more active Commercial Stone Way and the classic Seattle Single Family neighborhood, this site appeared to us as a space designated for small-scale, dense, rental housing. But in implementation, the zoning allowance does not reflect the true cost. A family-sized unit requirement, a one-time MHA fee payment, and construction complications made an apartment building at this site with the height and area restrictions infeasible. 

This Axonometric View of the surrounding blocks of the proposed project on Midvale Avenue North represents the existing zoning and development and in particular, it diagrams the different scales of surrounding residences and buildings between zones

While the MHA implementation unlocked this half block strip for potential multifamily redevelopment, higher density housing came with a family-sized unit requirement. For every 4 proposed units, one 2-bedroom (minimum 850 square feet) or for every two 2-bedroom units a single 3-bedroom unit (minimum 1,050 square feet) must be provided. In addition, any development under MHA (that does not provide affordable housing on site as part of the development) incurs a fee that must be paid to the city of Seattle before a building permit can be issued. The fee is a variable dollar amount per square foot that changes based on location within the City and the extent of the upzone. Alternatively, a project can choose to designate a portion of their units to rent for significantly less than market value for the first 75 years of the project. In our experience, the client almost always chooses the fee due to the complication of renting units through a city managed program and the future potential loss of rental income. At the same time, construction costs due to a lack of staging space on midblock sites, supply chain issues, and other national economic difficulties caused our client to rethink this project and focus elsewhere. The multiple requirements that previously would have made the projected income tight, but feasible, became too constricting as the project became short on projected rental income and desired number of overall units. We believe the zoning intended to create small apartment buildings with family-sized units, providing increased density near a commercial zone while also transitioning towards the more residential blocks of the existing neighborhood. Instead, due to the complexity described above, small townhouse structures and additional single family dwellings are being developed along this same zoning block. This is achieving a greater density than what previously existed, but still is creating single-family living at higher cost to future residents. Following the permitting of the small-scale 13-unit apartment building, our client chose to sell the site, resulting in the creation of a single family unit and a duplex structure.

As much as the City of Seattle needs to solve the lack of affordable housing and needs the addition of more family-sized rental units to the housing market, passing the cost of multiple housing initiatives - when applied at such small infill sites - onto the developer incentivizes the developer to avoid them entirely, where they instead pursue more predictable  projects with a greater financial upside and less risk.

Pictured is the proposed apartment project viewed from Midvale Ave N to the Northeast

An entry sequence was designed to bring residents and guest to the central open space of the site

The central space was designed to feel very open to allow air and light to activate the site and shared apartment spaces and to provide neighboring sites with massing relief

Fir Street

A very small site in Seattle’s Midrise Residential zone, the Fir Street project came to b9 architects as an apartment, proposed to take advantage of the increased capacity allowed under the MHA upzone. 

The site is located on a small peninsula of Midrise zone that is adjacent to the Yesler Terrace Master Planned Community and to the south of a small Neighborhood Commercial zone.  This site is visible from adjacent rights-of-way as it is surrounded by two parking lots and a garden owned by the neighboring Japanese Baptist Church to the west and the north, with an alley to the east. A pocket park is located across the street and the immediate context features many large new multifamily apartment structures that are part of the Yesler Terrace Master Planned Community.  

This Axonometric View of the surrounding blocks of the proposed project on E Fir Street and Broadway depicts the existing zoning and development and in particular, it diagrams the much larger scales of surrounding residences and buildings as well as the relative small size of the lot occupied by the proposed project.

The originally proposed massing for apartments on E Fir Street

The site dimensions and height allowance result in a vertical structure that helps anchor the pocket park across E Fir Street to the south and respond to the larger surrounding developments.  The proposal addresses this unique circumstance and emerges from a clear design concept. In response, the massing consists of an aggregation of “basalt columns” of various widths and heights.  These columns combine to create a subtle, yet dynamic building mass and landscape concept.  This design concept produces numerous modulations and material changes along all facades of the building.  The termination of the “columns” at different elevations along the facade creates opportunities for balconies, which further activate the facades of the building.

The project’s height is consistent with many of the newer buildings in the Yesler Terrace Master Planned Community to the south and west while the footprint is more consistent with the fourplexes, townhouses, and smaller apartment buildings to the east and north. Due to the small lot area, 2,400 square feet, the building would be unlike anything in the neighborhood. An innovative, 6-story apartment building, this Yesler Terrace project, touted by the DJC as an “infill infill project” would have yielded 15 rental units. The project was required to go through the city of Seattle’s Streamlined Design Review process as part of the permitting process.  Through this process, we proposed modifications to reduce the setbacks required in Seattle’s land use code in order to achieve the project goals of an infill apartment on this incredibly unique site. In our experience Design Review can and should allow for flexibility in order to respond to unique sites such as this one.  The design proposal was significantly less area than what is allowed by code. Unfortunately, the Design Review process resulted in a strict application of the land use code, eliminating the necessary area to make the “infill” infill apartment feasible. That, combined with the cost of construction, became untenable and so the project shifted to a less risky townhouse scope.

The proposed massing for the project featuring 15 units provided on site

The current proposal for 3 townhomes on the same site, currently in process

The height and capacity allowance in the Midrise zone, does not have the incentives necessary to take full advantage when the site does not conform to certain characteristics including size, access to utilities such as storm and sewer, and being clear of environmental critical areas like steep slopes or wetlands. While b9 architects, inc. enjoys designing townhouses and seeing their impact on the City, we recognize a need for a variety of housing solutions.

Over the past 20 years, b9 architects has garnered expertise in maximizing Seattle’s sites in smart and well-designed ways. Clients often choose our firm to help them navigate difficult sites, or design innovative projects to compete with larger rental properties down the street. In our experience, these small 10-30 unit infill apartments tend to be the projects most difficult to meet the financial model necessary to build. If the market isn’t completely on board, developers stop completely or change typology.

In 2023, we hope to explore ways to incentivize small and medium multifamily solutions to help our clients and partners better achieve the combined goals of better, denser, and more affordable housing in Seattle’s neighborhoods.  This will include examining the necessary code changes to expand the access to housing opportunities and levels of affordability in the current Neighborhood Residential zones.