Editor’s note: In 2023, Sightline helped pass bills in both Washington and Oregon that prompted those states’ building code councils to develop new code to allow what you might call “sunlight suites.” They’re often dubbed “single-stair apartments,” but that name can mislead, since plenty of these buildings feature elevators and the homes themselves can be spacious. Additional fire safety measures such as shorter travel distances and more sprinkler coverage eliminate the need for a second staircase. This enables skinnier buildings that fit well on small lots, and at the same time, opens up room for family-sized homes with windows on more sides for better light and air.
Seattle’s 1977 building code set the example for those statewide efforts, and today the city features hundreds of sunlight suites serving a range of needs. From market-rate rentals and condos to cohousing options, student housing to affordable housing, sunlight suites are providing attractive, enviably located homes at various price points in places that need them. As Oregon and Washington consider new statewide building codes that legalize them, other cities and towns can take note—and inspiration.
Below, we reprint a photo-rich article from the Mercatus Center about sunlight suites, adapted and edited slightly for Sightline audiences.
Built in 1978 with a view of Seattle’s historic Pike Place Market, the Pike and Virginia Building initiated a housing style unique to US cities: sunlight suites. 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 or elevator.1
The Pike and Virginia Building, the very first building of sunlight suites in the city, is a narrow six-story condominium tower made possible by 1977 building-code amendments. In an effort to reverse the city’s population decline, Seattle’s then-Mayor Wes Uhlman formed an advisory committee that recommended these changes. 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” and recommended amendments to legalize taller single-stair housing within the city.2
The adoption of these unique amendments allowed the Pike and Virginia project to build more than a dozen homes using a compact footprint and slender form 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 they enable a prolific building type used for new housing across Seattle.
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 But 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—just three stories.4 In contrast, Seattle diverged from the national model code after experts there evaluated how egress requirements were reducing housing options in the city. They then 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, with doors on both sides of a long central hallway that runs between the two stairwells. For single-stair housing, though, Seattle’s building code requires very short distances from units to exit (or “egress”) stairs. This results in efficient floor plates that dedicate more of the floor plan to living areas than typical double-loaded corridor housing designs do.
Clustering apartments around a central stair or elevator creates a compact building footprint that fits on small lots, enabling more infill opportunities and also avoiding the substantial cost of assembling multiple parcels needed for larger buildings. And since Seattle’s code limits the number of homes per floor to four, developers tend to make them larger, with windows on multiple walls that provide lots of natural light and allow cross-ventilation.
With apartments ranging from 220-square-foot micro-units to 2,000-square-foot multiple-bedroom, full-floor flats, Seattle’s collection of sunlight suites boasts a diversity of home types and sizes that is missing from small-lot infill in other cities across the United States.
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 them up to six stories, it does so with more restrictions than Seattle. These restrictions include a requirement for steel or concrete construction—a general rule for all construction throughout New York City—and a floor area limit of only 2,000 square feet per story. Legislation to double this size limit for sunlight suites projects 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 legalizing taller sunlight suites housing. In 2012, Honolulu’s policymakers adopted building code amendments copied verbatim from Seattle’s single-egress provisions, and in 2023 and 2024, multiple states passed legislation aimed at reforming means of egress rules around stairs to expand housing options.5
Increased attention to these building types 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 lobbying both for and against taller single-stair buildings. The NFPA plans to publish a report to help policymakers understand fire and other safety considerations.
Below are showcased six categories of recently constructed projects made possible by Seattle’s unique building-code approach:
Readers can also view a spreadsheet summary and map of the 23 projects listed.
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 “missing middle housing.”
Small lots are often overlooked for their ability to create urban density. Allowing the construction of midrise single-stair housing offers US cities the chance to support more housing types and create denser, more walkable communities in the existing urban fabric.
1. Market-rate apartments
ALNA Ballard
ALNA Ballard is one of the few apartment buildings in Seattle’s low-rise zoning and sits on a block consisting of single-detached houses and three-story townhomes.
- Architect: b9 Architects
- Address: 1123 NW 57th St
- Neighborhood: Ballard
- Number of units: 21
- Lot size: 50′ x 100′ (5,000 square feet)
- Year completed: 2022
- Floor Area Ratio (FAR): 2.1
Greenfire Campus Apartments
The Greenfire Campus Apartments complement a compact footprint with access to urban gardens and natural habitat.
- Architect: Johnston Architects
- Address: 2041 NW 57th St
- Neighborhood: Ballard
- Number of units: 18
- Lot size: Shared campus with retail building
- Year completed: 2013
Franklin Station
Franklin Station features a shared roof deck and includes a mix of micro and two-bedroom homes on a small corner lot.
- Architect: Diepenbrock Architects
- Address: 2303 Franklin Ave E
- Neighborhood: Eastlake
- Number of units: 22
- Lot size: 60′ x 80′ (4,800 square feet)
- Year completed: 2019
- FAR: 2.5
Sola16
Sola16 replaced one single-detached house with eight family-sized, two-bedroom homes. A central circulation core containing a stair, elevator, and corridor separates units, so neighbors do not share internal walls.
- Architect: Schemata Workshop
- Address: 2351 Franklin Ave E
- Neighborhood: Eastlake
- Number of units: 8
- Lot size: 60′ x 90′ (3,600 square feet)
- Year completed: 2016
- FAR: 3.1
602 Flats
602 Flats consists of four full-floor homes, so each apartment features natural light and ventilation on all four sides.
- Architect: BUILD LLC
- Address: 602 12th Ave E
- Neighborhood: Capitol Hill
- Number of units: 4
- Lot size: 40′ x 65′ (2,600 square feet)
- Year completed: 2018
- FAR: 2.0
Sylvan Court
Following a change to local parking requirements, Sylvan Court transformed a surface parking lot into 20 homes in a four-story addition to an existing three-story apartment building.
- Architect: David Neiman Architects
- Address: 1901 E Fir St
- Neighborhood: Yesler Terrace
- Number of units: 20
- Lot size: 30′ x 130′ (3,900 square feet)
- Year completed: 2021
- FAR: 2.7
Jansen Court
On a very narrow lot, the Jansen Court sunlight suites were constructed in the side yard of an existing century-old single-detached house.
- Architect: CAST architecture
- Address: 2010 E Jansen Ct
- Neighborhood: Capitol Hill
- Number of units: 10
- Lot size: 30′ x 120′ (3,600 square feet)
- Year completed: 2022
- FAR: 1.3
Juniper Flats
Juniper Flats is a 12-home sunlight suites building that maximizes the potential of its small lot while maintaining a scale relatable to adjacent single-detached houses.
- Architect: BUILD LLC
- Address: 6547 24th Ave NW
- Neighborhood: Ballard
- Number of units: 12
- Lot size: 50′ x 102′ (5,100 square feet)
- Year completed: 2024
- FAR: 1.5
Fremont View
Completed in fall 2024, the 29-unit Fremont View Apartments is located on a steep hillside and shares a lot with an existing multistory apartment building. Taking advantage of the terrain, the narrow seven-story project consists of two separate single-stair sections stacked on top of each other. The bottom three floors are served by an elevator and by a single, enclosed stairway that exits at the street level on the building’s south side, and the top four floors are served by a separate, open stairway that exits at the top of the hill on the building’s north side.
- Architect: BUILD LLC
- Address: 519 N Bowdoin Pl
- Neighborhood: Fremont
- Number of units: 29
- Lot size: 80′ x 120′ (9,000 square feet)
- Year completed: 2024
- FAR: 2.2
2. Condominiums
Dexter Condominiums
The four-story Dexter sunlight suites sit on an urban lot zoned with a 40-foot height limit overlooking Seattle’s Lake Union. The project contains eight luxury condominiums, each with windows on three sides.
- Architect: Johnston Architects
- Address: 2514 Dexter Ave N
- Neighborhood: East Queen Anne
- Number of units: 8
- Lot size: 90′ x 100′ (9,000 square feet)
- Year completed: 2024
- FAR: 1.8
Two Ten Comstock
Neighboring both a single-detached house and a six-story, 40-unit apartment building, Two Ten Comstock provides a much-needed housing type in Seattle: urban condominiums.
- Architect: Prentice Balance Wickline Architects
- Address: 210 W Comstock St
- Neighborhood: Queen Anne
- Number of units: 8
- Lot size: 60′ x 110′ (5,700 square feet)
- Year completed: 2018
- FAR: 2.6
East Union Lofts
Seattle’s East Union Lofts is the oldest of the projects featured in this article, having been completed in 2001. It activated a narrow lot with full-depth units so that residents enjoy full-height windows on the front and rear of the building, which allow for breezy cross-ventilation. The project’s raw and disciplined design earned recognition and awards from AIA Seattle, AIA Washington, and AIA NW & Pacific Region.
- Architect: Miller Hull
- Address: 1310 E Union St
- Neighborhood: Capitol Hill
- Number of units: 8
- Lot size: 40′ x 80′ (3,200 square feet)
- Year completed: 2001
- FAR: 5
The Fitzgerald
The Fitzgerald contains 13 large three-bedroom condo homes, each with abundant daylight from windows on multiples sides of the project’s unusual L-shaped lot.
- Architect: Johnston Architects
- Address: 1406 3rd Ave W
- Neighborhood: Queen Anne
- Number of units: 13
- Lot size: L-shaped (9,300 square feet)
- Year completed: 2023
- FAR: 2.3
3. Student housing
15th Avenue Apartments
The 15th Avenue Apartments feature eight large three- and four-bed apartments for college students on a narrow lot in Seattle’s walkable University District.
- Architect: Novion Group
- Address: 5234 15th Ave NE
- Neighborhood: University District
- Number of units: 8
- Lot size: 40′ x 110′ (4,400 square feet)
- Year completed: 2016
- FAR: 1.8
University Flats
The University Flats building provides a range of home sizes, from micro to two-bedroom, with excellent daylight and views.
- Architect: Neiman Taber Architects
- Address: 5521 15th Ave NE
- Neighborhood: University District
- Number of units: 18
- Lot size: 40′ x 100′ (4,000 square feet)
- Year completed: 2020
- FAR: 2.4
The Willet
The Willet used a compact and efficient floor plate to replace a single-detached house with 18 units on a narrow lot. The homes are within walking distance of the University of Washington campus.
- Architect: Ryan Rhodes Designs
- Address: 4252 8th Ave NE
- Neighborhood: University District
- Number of units: 18
- Lot size: 40′ x 100′ (4,000 square feet)
- Year completed: 2017
- FAR: 2.0
4. Affordable housing
Capitol View
This five-story condominium is the largest multifamily project Habitat for Humanity has ever built anywhere in the US, and it created affordable homeownership opportunities for Seattle residents.
- Architect: JW Architects
- Address: 410 11th Ave E
- Neighborhood: Capitol Hill
- Number of units: 13
- Lot size: 40′ x 100′ (4,000 square feet)
- Year completed: 2023
- FAR: 2.9
Aurora Avenue Apartments
The Aurora Avenue Apartments sit on a lot just 30 feet wide. They replaced a single-detached house with a collection of 13 affordable homes. All of them have cross-ventilation, and the upper-level units include balconies.
- Architect: Jerry Jutting Architect
- Address: 3833 Aurora Ave N
- Neighborhood: Fremont
- Number of units: 13
- Lot size: 30′ x 80′ (2,400 square feet)
- Year completed: 2017
- FAR: 1.9
5. Mixed-use housing
101 John Street
Only blocks from the Space Needle, the 101 John Street Apartments are a long, narrow bar of four large, street-facing homes per floor and a circulation core on the rear. The ground floor features a deli and a salon.
- Architect: Kilburn Architects
- Address: 101 John St
- Neighborhood: Belltown
- Number of units: 20
- Lot size: 40′ x 115′ (4,600 square feet)
- Year completed: 2016
- FAR: 5.4
BB House
The BB House apartments were constructed as part of a renovation and addition to a century-old retail building and create a new mixed-use project.
- Architect: PUBLIC47 Architects
- Address: 1208 E Remington Ct
- Neighborhood: Yesler Terrace
- Number of units: 22
- Lot size: 80′ x 90′ (7,200 square feet)
- Year completed: 2024
- FAR: 1.9
Park Modern
Designed, developed, and built by BUILD LLC, the mixed-use Park Modern sunlight suites boast a large floor plate and provide 12 full-depth condominiums atop three ground-floor commercial spaces and below-grade parking.
- Architect: BUILD LLC
- Address: 5611 University Way NE
- Neighborhood: University District
- Number of units: 12
- Lot size: 75′ x 90′ (6,750 square feet)
- Year completed: 2007
- FAR: 2.7
Admiral Mixed-Use
The Admiral Mixed-Use project contains four condominiums per floor, each with access to a balcony and windows on multiple sides. The ground floor contains tuck-under parking and a childcare center.
- Architect: NK Architects
- Address: 2310 California Ave SW
- Neighborhood: West Seattle
- Number of units: 12
- Lot size: 50′ x 123′ (6,150 square feet)
- Year completed: 2020
- FAR: 3.2
6. Cohousing
Capitol Hill Urban Cohousing (CHUC)
CHUC is one of the most innovative urban housing projects in the United States. The cohousing project was designed and developed by the residents and uses a five-story single-stair design to provide nine homes facing a central courtyard.
- Architect: Schemata Workshop
- Address: 1720 12th Ave E
- Neighborhood: Capitol Hill
- Number of units: 9
- Lot size: 40′ x 110′ (4,400 square feet)
- Year completed: 2016
- FAR: 4
