The Seattle Special: A US City’s Unique Approach to Small Infill Lots

Built in 1978 with a view of Seattle’s historic Pike Place Market, the Pike and Virginia Building (figure 1) initiated a housing style unique to US cities. Locally dubbed the Seattle Special, this type of housing is a multifamily dwelling built up to six stories in height, constructed with a small footprint on an urban lot, also known as an infill lot, and served by a single staircase.[1]

 FIGURE 1. Pike and Virginia Building (1978), Olson Walker Architects

_{^{Photograph courtesy of Andrew Van Leeuwen Photography.}}

The Pike and Virginia Building, the very first Seattle Special, is a narrow six-story condominium tower made possible by 1977 building-code amendments drafted at the recommendation of an advisory committee formed by Seattle’s Mayor Wes Uhlman to reverse the city’s population decline. The committee, known as the Building Code Advisory Board, was tasked with examining how the building code could be modified to “encourage in-city living, redevelopment, and new construction”[2] and recommended amendments to legalize taller single-stair housing within the city. The adoption of these unique amendments allowed the Pike and Virginia project to build more than a dozen units using a compact-footprint and slender-massing design that met strict urban-design guidelines. Though the amendments have evolved over the decades, they have maintained the original spirit that first encouraged the development of dense housing on small urban lots, and today the Seattle Special is a prolific building type used for new housing across the city.

In response to today’s housing crisis in the United States, building-code reform has drawn attention from US politicians and housing advocates looking to make housing more attainable.[3] With a three-story height limit, the most commonly used model code in the United States, the International Building Code (IBC), mandates one of the most restrictive height limits in the world for single-stairway multifamily buildings.[4] In contrast, the Seattle Special diverged from model code requirements after experts in Seattle evaluated the impact that egress requirements were having on housing options in the city and created measures for taller single-stair housing of any construction type, including wood, steel, and concrete.

Typical IBC-compliant apartment buildings taller than three stories have double-loaded corridors, whereby a required central corridor bisects the building to provide access to multiple exits, resulting in a wide footprint. For single-stair housing, Seattle’s building code requires very short distances from units to exit stairs, resulting in highly efficient floor plates that dedicate a larger portion of the floor plan to living areas than typical double-loaded corridor housing floor plates do. Clustering units around a central stair creates a compact floor plate that fits on small lots, avoiding the substantial costs of assembling the parcels needed for larger buildings, and since Seattle’s code limits the number of units per floor to four, typical units have windows on multiple walls, providing a high quality of living.

With apartments ranging from 220-square-foot micro units to 2,000-square-foot multiple-bedroom, full-floor flats, Seattle’s collection of Seattle Specials boasts a diversity in housing that is missing from small-lot infill in cities across the United States. Seattle Special projects increase the housing supply by bringing dense housing to small lots and adding units across the housing spectrum, including affordable housing, market-rate apartments, student housing, and mixed-use luxury condominiums.

Currently, Seattle, Honolulu, and New York City are the only US cities that allow single-stair housing up to six stories in height. While New York City permits new single-stair buildings up to six stories, it does so with more restrictions than Seattle has and with a requirement for steel or concrete construction—a general rule for all construction throughout the city—and a floor area limit of only 2,000 square feet per story. Legislation to double this size limit was introduced in 2022, aligning New York City’s regulations more closely with Seattle’s. Also following Seattle’s lead, other municipalities throughout the United States have legalized or are considering legislation allowing taller single-stair housing. In 2012, Honolulu’s policymakers adopted building-code amendments copied verbatim from Seattle’s single-exit provisions, and in 2023 and 2024, multiple states passed legislation aimed at reforming means of egress rules around stairs in order to improve housing options.[5] Increased attention on these buildings led the National Fire Protection Association (NFPA) to host a two-day Single-Exit Stair Symposium in September 2024 that brought together international fire-safety experts and advocates for and against taller single-stair buildings. The NFPA plans to publish a report that policymakers can use as a resource to understand fire and other safety considerations.

The gallery section of this policy brief showcases six categories of recently constructed projects made possible by Seattle’s unique building-code approach:

1. Market-rate apartments
2. Condominiums
3. Student housing
4. Affordable housing
5. Mixed-use housing
6. Cohousing

These compact buildings are located on height-zoned lots too small to accommodate the typical double-loaded corridor apartments. The examples, which have 4 to 29 units, demonstrate how building-code reform can transform small urban infill lots into the dense and vibrant developments referred to by housing experts as the “missing middle housing.”

Small lots are often overlooked for their ability to create urban density, and allowing the construction of mid-rise single-stair housing offers US cities the chance to support more housing types and create denser, more walkable communities in the existing urban fabric, whether in a historic district like Pike Place Market or an emerging neighborhood yet to make a name for itself.

Gallery of Small Infill Lots

1. Market-rate apartments

ALNA Ballard

_{^{Photograph by Alex Hart Photography.}}

This project is one of the few apartment buildings in Seattle’s low-rise zoning and sits on a block consisting of single-family homes and three-story townhomes.

• Architect: b9 Architects
• Address: 1123 NW 57th Street
• Number of units: 21
• Lot size: 50' x 100' (5,000 square feet)
• Year completed: 2022

Greenfire Campus Apartments