Single Stair Reform

Single stair apartment buildings allow more windows per unit and accommodate family-sized apartments on small lots. Image: OCFRealty

Single Stair buildings refer to residential buildings between four and six stories with only one staircase. Currently, it is typical for 4-6 story apartment buildings in the US to require two sets of stairs with a hallway connecting them. The requirement for two stair cases was implemented before the advent of modern technology that helps contain fires from spreading. Evidence suggests, when modern fire suppression technology is in place, the fire safety of single stair buildings is identical or better to that of buildings with two stairwells.

Though not requiring the second staircase may seem like a small reform, the benefits can be massive. They include the following:

• More multifamily units on smaller lots, which are often near the core of a city.

• More 2- and 3-bedroom units suitable for families.

• More “corner” units with more natural light and better cross-ventilation.

• Housing affordability.

• Shorter construction project duration.

• Higher rates of ownership opportunities.

• Due to smaller scale, developers have easier times securing financing and building incrementally.

• Small, local construction firms have a better chance to compete in the market.
  
  

In Phoenix, there are many 50-foot lots that are simply not wide enough to support buildings with two staircases. But single stair buildings could potentially fill those lots, adding much needed housing supply and filling underutilized/vacant lots in our most transit-rich areas.

Models from Peer Cities: 

• Austin: Legalized single-stair buildings up to 5 stories in April 2025.
  
  

• Nashville: Legalized single-stair construction with up to 4 units per floor in July 2025.
  
  

• Knoxville: Adopted the 2024 International Building Code with local amendments in 2024 that legalized single-stair multi-family buildings.
  
  

• Seattle: Legalized single-stair buildings in 1977 up to 6 stories with smoke-protected or exterior stairs, sprinklers, and limits of 4 units/floor.
  
  

• Honolulu: Replicated Seattle’s model in 2012.
  
  

• Dallas: Permits “scissor stair” designs for 5–6 story buildings where the two staircases are allowed to be next to each other rather than separated, offering many of the same benefits as a single-stair building.
  
  

• Chicago: Allows single-stair townhouses up to 4 stories.
  
  

• New York City: Since 1968, New York City’s building code has provided special provisions for small single-stair apartment buildings. Today there are two main options: 

• Up to four stories where each floor is no larger than 2,500 sq ft and limited to three dwelling units per story. These buildings must use Type I or II construction, have a two-hour rated stair enclosure with 1½-hour self-closing doors, and be fully sprinklered.

• Up to six stories where each floor is no larger than 2,000 sq ft, also built with Type I or II construction and sprinklers; the three-units-per-floor limit does not apply in this path.

• As of 2025, research by the Pew Charitable Trusts found over 4,400 modern single-stair apartment buildings in New York City. These provisions, introduced in the 1968 code, remain a distinctive feature of NYC’s mid-rise housing rules.

Image: OurCulver