Single-stair Housing Innovation Part II: Exploring Seattle Development
By Kyle and Ian • Apr 23rd, 2025
Single stair
Local spotlight
Seattle
Greetings from Cedar!And welcome back to our series on single-stair reform!In Part I, we covered the recent news out of Austin City Council allowing for single-stair buildings to be built citywide.Today in Part II, we'll jump to Seattle to explore its implementation of single-stair buildings. Our team analyzed Seattle's regulatory framework and built examples (so you don't have to) to better understand how these projects are successfully developed while meeting all safety requirements.In Part III of this series, we'll officially unveil Cedar's product design for the next generation of single-stair buildings, designed for Austin and built to scale. Stay tuned for the launch in May!
Design solutions from Seattle
market proven, with over 30 buildings delivered (that we know of)
market proven, with over 30 buildings delivered (that we know of)
602 FlatsFourplex
Juniper FlatsTwelveplex
The WilletStudent Housing
An expanded catalog of building (and home) types
with 30+ years of development to learn from.
with 30+ years of development to learn from.
Seattle's code for single-stair buildings requires:
• Maximum four units per floor (same as Austin)• Maximum height of six stories (but still limited by Type V construction)• Maximum travel distance of 125ft (same as Austin, IBC compliant)
Density Profile
Our analysis of Seattle has determined that there are two distinct categories for single-stair projects:a. Maximized unit count on smaller sites.
Typically student housing or renovations to sites with existing buildings.b. Maximized floor area on larger sites.
Multiplex buildings (3-12 units) that offer better unit layouts on larger sites.
Better homes without compromising on safety
single-stair buildings present new opportunities for better living.
single-stair buildings present new opportunities for better living.
2xMore Light
Every unit is potentially a corner unit - giving each apartment more windows than comparable units in a double-loaded apartment.1
40%More Air
Studies show the ventilation rate (ACH - Air Changes Per Hour) for most corner units is 40% more effective than single-fenestrated units.2
6-13%Cost Savings
Needing to construct only one stair and significantly smaller hallways reduces average construction costs.3
24%More Unit Types
Because hallways take up less space in the floor plan, larger unit layouts are possible.4
0%More Fire Incidents
Studies in NYC and Seattle both show there are fire-related risks are not higher in single-stair buildings.5
Questions?
Schedule a time below to learn more about Cedar or share your feedback.1AIA Austin (2024). Technical Code Amendment - Single Stair. https://aiaaustin.org/wp-content/uploads/2024/10/AIA-Austin-Single-Stair_240618_Fire-Safety-Diagrams.pdf
2AIA Austin (2024). Technical Code Amendment - Single Stair. https://aiaaustin.org/wp-content/uploads/2024/10/AIA-Austin-Single-Stair_240618_Fire-Safety-Diagrams.pdf
3Public Architecture (2023). Single Stair Residential Buildings, p. 22. BC Housing & CMHC. https://www.bchousing.org/sites/default/files/media/documents/Single-Stair-Residential-Buildings-PUBLIC.pdf
4Public Architecture (2023). Single Stair Residential Buildings, p. 22. BC Housing & CMHC. https://www.bchousing.org/sites/default/files/media/documents/Single-Stair-Residential-Buildings-PUBLIC.pdf
5Horowitz, A. (2025, February 27). Small single-stairway apartment buildings have strong safety record. Pew Trusts. https://www.pewtrusts.org/en/research-and-analysis/reports/2025/02/small-single-stairway-apartment-buildings-have-strong-safety-record
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