California weighs single-stair multifamily to ignite housing supply

California’s emerging housing fracas over a single stairwell may become a lightning rod, affecting both building codes and capital investment in more multifamily projects in more places.

California’s Fire Marshal is reportedly in the final stages of a report due this month on whether the state will allow single‑stair multifamily buildings above three stories, and on when and how they may be permitted.

Whatever the report concludes, the matter has become a flashpoint regarding how far policymakers will go to support investment models for affordable multifamily housing in an era of stubbornly high costs.

Changing single‑stair regulations could add a new dimension to the state’s years‑long effort to address acute affordability challenges and spark new solutions.

The efforts – and ones like it – are bubbling up amid intensifying national debates over how building codes can either unlock or continue to choke off new supply.

“It really is a scenario of trying to resolve the housing problems at many different levels,” said Phillip Babich, a land use attorney with global law firm Reed Smith’s San Francisco office.

While California typically leads the nation in zoning legislation, Colorado, Montana, Texas, New Hampshire, and Tennessee have been out ahead in adopting this building code change.

New York City and Seattle have allowed single‑stair construction up to six stories since 2012.

Minnesota recently completed its own study, which concluded that single‑stair construction up to six stories can be safe when other fire safety conditions are in place.

California lawmakers, however, will not have to look outside the state’s borders for a test case.

In September 2025, Culver City legalized six‑story single‑stair apartments, becoming the state’s first jurisdiction to do so.

City leaders cast their ordinance as both a housing-affordability tool and a real‑world pilot to win support from state regulators and capital markets.

Studying change to make change

Rather than immediately rewriting the California Building Standards Code, lawmakers passed legislation in 2023 that launched a fresh study process now at the center of the debate.

Current multifamily residential safety rules typically require at least two enclosed stairs and exits for most buildings taller than three stories.

Such a standard dictates a building’s shape, circulation, and the number of homes that can fit on a specific property site.

Developers and architects contend that the second stair is not just a life‑safety feature but also a design requirement with a ripple-effect on a project’s budget and unit-cost constraints. They argue that an additional staircase consumes non-leaseable floor area and increases structural and mechanical costs.

Eliminating one stair and its associated corridor can trim structural concrete, shafts, and other non‑revenue‑generating space. Doing so frees up more of the project budget for livable square footage. More efficient floor plates, they argue, allow developers to reallocate hard costs to support either more units or larger two‑ and three‑bedroom homes that families can use.

Such layouts could ease the prevailing trend toward concentrating new construction in small luxury studios.

Why infill sites matter most

The stakes are highest on tight urban infill sites, where fitting two compliant stairs can be the dividing line between projects that pencil and those that don’t.

In today’s realities, a single stair option could be the difference between a surface parking lot and a viable small apartment building. Incremental new supply on such sites can help ease rent pressures at the neighborhood scale.

That prospect is one reason the debate has drawn close attention from lenders and investors. They view stair and core design as a capital calculus pivot point for unit mix, yield and perceived tenant appeal.

Architects also frame single‑stair reform as a design and livability issue, not just a cost question. Single‑stair layouts, they say, can produce wider units with windows on two sides, better suited for families. Those units can be less dependent on the “luxury micro‑unit” model that dominates many elevator‑served high‑rises.

Because many of these buildings are four‑ to six‑story walk‑ups, they can sometimes avoid elevators or rely on smaller cores. That shift reduces both construction and long-term operating expenses that are ultimately reflected in rents or homeowners’ association fees.

Safety questions and safeguards

Safety remains the central political and technical obstacle. Reed Smith’s Babich said that “fire safety concerns were very much front and center” in the working group meetings. “But what are the risks of not housing people?” he noted.

California’s study is unfolding alongside evidence that small single‑stair buildings have a strong life‑safety record under modern codes. That record appears strongest when designers pair single stairs with sprinklers and compartmentalized construction.

A Pew Charitable Trust study last year found that “single-stairway four-to-six-story apartment buildings have fire performance at least as good as their two-stairway counterparts.” Any state‑level change is expected to include guardrails, such as caps on floorplate depth and units per floor.

Observers also expect full sprinklers and, where applicable, pressurized stairs, calibrated to meet the 2027 International Building Code. That model code will allow single‑stair apartments up to four stories and will likely mirror standards in peer cities.

Watching other cities and the next moves

California’s major urban peers already offer a glimpse of what the state might embrace or reject. New York City and Seattle provide the built precedents that many California stakeholders cite. Los Angeles has directed staff to draft its own single‑exit, single‑stair ordinance modeled in part on Seattle. The final thresholds and technical details of that ordinance remain under negotiation.

What happens next will shape not just code manuals but also business and capital pro formas, and the projects and floor plans that get funded. A green light from Sacramento would give lenders, architects, and cities cover to treat single‑stair walk‑ups as standard, not speculative.​

If the state opts for a narrow pilot instead, the most inventive single‑stair projects may remain confined to a few coastal cities, even as the housing shortage spreads far beyond them. Either way, the stair tower is about to become a front‑line test of how much design risk California will tolerate in exchange for more homes.