AB 2252: The Code Change That Could Unlock California’s Missing Middle

What’s the problem?

California’s building code currently requires most multifamily residential buildings above three stories to have two separate stairwells. That requirement, rooted in older fire safety standards, has a cascading effect on building design. Double-stair buildings need a central corridor connecting both cores, which pushes units to the edges, limits floor plate flexibility, and makes smaller infill sites more economically infeasible. The result: fewer units, less variety in unit types, and higher per-unit costs.

 In terms of affordability, single-stair buildings cost less to build and can fit on smaller lots, two things that directly expand where and how much housing gets built in California. The Pew Charitable Trusts estimates that single-stair four-to-six-unit buildings cost roughly 6 to 13 percent less to build than comparable dual-stair designs, in part because they sit on narrower lots and use simpler cores. 

How we got here

The State Fire Marshal’s workgroup — mandated by AB 835 and completed ahead of the 2026 session — reached a clear consensus on buildings up to four stories: single-exit construction is viable with appropriate conditions. Those conditions include full sprinklers throughout the building, a maximum of four units per floor with no more than 4,000 square feet per floor, a maximum 20-foot corridor travel distance to the stair, no occupied rooftops, and no electrical receptacles in stairwells. For six-story buildings, the workgroup did not reach consensus and recommended further study.

AB 2252 takes that recommendation seriously — directing HCD to develop standards for single-exit buildings up to six stories, in consultation with the State Fire Marshal, for inclusion in the next triennial edition of the California Building Standards Code (Title 24). 

Local governments are already moving

California cities haven’t waited for the state. Culver City passed a single-stair exit ordinance (Ordinance No. 2025-013 / Resolution No. 2025-071) that was formally accepted for filing by the California Building Standards Commission, amending Title 24 to allow single-exit configurations in 4–6 story residential buildings, with an elevator requirement for 5–6 story buildings. San José, meanwhile, voted to study allowing six-story single-stair apartments, with Assemblymember Lee calling it an example of “proven common sense solutions.”

These local efforts are promising — but they’re constrained. The AB 130 code freeze, in effect through 2031, limits cities’ ability to adopt local building standard amendments. AB 2252 directly addresses this by carving out an explicit exception, giving other jurisdictions a clear legal pathway to follow Culver City’s lead without waiting years for the next state code update. 

What this means for HAC members

For developers and architects working in California’s urban infill market, single-stair reform isn’t an abstract policy win, it’s a practical tool. Double-stair requirements effectively set a floor on building width, which rules out a significant share of urban lots where housing is most needed. Single-stair buildings can work on narrower parcels, produce a wider range of unit layouts (including larger family-sized units that are hard to make pencil under current configurations), and reduce overall construction cost per unit by eliminating the second core and associated circulation space. Projects in the 4–6 story range are the sweet spot for wood-frame construction on infill sites, rendering it potentially one of the most impactful code changes in years. If you have sites that have stalled or been shelved because of stairwell constraints, AB 2252’s local exemption provision means some California cities could move before the next code cycle. It’s worth revisiting those projects now.

HAC members interested in engaging on AB 2252 — whether through testimony, letters of support, or coalition sign-on — should reach out to ali@housingactioncoalition.org. Your project experience and design expertise are exactly what legislative staff need to hear as this bill advances.