While the national conversation on housing affordability has been dominated by the high-profile debate over zoning reform—specifically the push for upzoning and the legalization of accessory dwelling units (ADUs)—a quieter, more technical revolution is unfolding in the world of building codes. For developers and architects, the most significant barriers to creating "missing middle" housing are often not found in zoning maps, but in the rigid, granular requirements of building codes that dictate how a structure must be built.
Washington state, currently grappling with one of the most severe housing affordability crises in the nation, has emerged as the vanguard for this movement. In March, the state took a landmark step by signing legislation that allows for "scissor stairs" in multifamily construction—the first state in the U.S. to do so. This move, which takes effect on June 11, represents a paradigm shift in how urban infill projects will be designed, financed, and built.
The Chronology of Change: From Single-Stair to Scissor Stairs
The path to this reform was neither sudden nor simple. For years, housing advocates and urban planners argued that the U.S. building code’s insistence on two, widely separated stairwells for virtually every multifamily project—regardless of size—was an antiquated relic that inflated costs and killed projects on narrow urban lots.
The movement began in earnest with the push for single-stair reform. By allowing smaller buildings (typically six stories or fewer) to be served by a single, fire-rated egress stairwell, planners realized they could maximize floor plates, improve unit layouts, and reduce the "dead space" that dual-stairwell requirements mandated. Washington successfully moved the needle on this, with the State Building Code Council currently racing toward a July 1, 2024, deadline to finalize amendments that allow single-stair construction statewide.
However, advocates realized that single-stair reform, while transformative for small infill, did not solve the challenges facing taller, mid-rise developments in dense urban corridors like Seattle and Bellevue. Thus, the conversation shifted to scissor stairs.
The legislative journey reached its apex this spring. After intensive lobbying by housing policy groups and architects who argued that current codes were rendering thousands of urban parcels economically unviable, the legislature passed the bill, which was signed into law by Governor Bob Ferguson in March. This legislation doesn’t just suggest a change; it mandates that the state revise its construction codes to permit the scissor stair configuration, setting the stage for a rollout that will conclude with finalized rulemaking by 2027.
Understanding the Mechanics: Single Stair vs. Scissor Stair
To understand why this is a "game-changer," one must look at the geometry of modern apartment design.
The Single-Stair Model
Single-stair reform is designed for "missing middle" housing—buildings that bridge the gap between single-family homes and massive apartment blocks. By allowing one stairwell in a building of up to six stories, architects can create "point access" blocks where every unit is a corner unit, enjoying light and air from multiple sides. This is an efficient, human-scale design that has been the standard in Europe and parts of Canada for decades.
The Scissor Stair Innovation
Scissor stairs serve a different purpose: they address the "tall and thin" building dilemma. In a traditional dual-stairwell setup, two separate shafts must be carved out of the building’s core, usually at opposite ends of the hallway. In a narrow, urban infill lot, these two shafts occupy a disproportionate amount of the floor plate, often forcing architects to shrink the size of units or, worse, preventing the building from being wide enough to house a functional apartment layout entirely.
A scissor stair configuration uses two interlocking stairways that crisscross within a single, fire-rated shaft. By folding these two separate paths of egress into one footprint, architects reclaim valuable floor area. It effectively doubles the efficiency of the egress core.
The Economic Implications: Data-Driven Development
The impact of this reform is not merely architectural; it is profoundly economic. In the hyper-expensive markets of Seattle and the tech-centric Puget Sound region, where companies like Microsoft and Amazon drive intense demand for housing, every square foot is a calculation of profit or loss.
Cost-Benefit Analysis
Research from groups like the Sightline Institute suggests that integrating scissor stairs can reduce total construction costs by between 6% and 13% per building. Even when accounting for the heightened fire-protection requirements necessitated by the shared shaft, the net gain in leasable square footage is substantial.
For a mid-rise development in a city like Bellevue, where the cost per square foot of construction is among the highest in the country, a 10% reduction in costs represents hundreds of thousands, if not millions, of dollars in savings. These savings act as a powerful incentive for developers who have previously walked away from "tight" urban lots, believing them to be unbuildable under existing code.
Official Responses and the Road Ahead
The reaction to the new law has been largely positive among the development and urbanist communities, though the process of implementation remains cautious.
"Scissor stairs are a design feature common in other countries but rare in most US cities," wrote Seattle urban planner Markus Johnson. "They help save more of a building’s interior square footage for homes, while still providing two fire-safe staircases for residents and emergency responders."
However, the transition will not happen overnight. The law mandates the formation of an advisory committee under the State Building Code Council to hammer out the specific safety protocols. Fire safety advocates have historically been the primary obstacle to such changes, citing concerns over smoke management and the complexity of emergency egress during a blaze. The rulemaking process, which will be exhaustive, is expected to last through 2027 to ensure that the scissor stair design meets the highest modern fire-safety standards.
Broader Implications: Will the Rest of the Nation Follow?
Washington’s leadership on this issue places it at the center of a national experiment. If the state can successfully integrate scissor stairs into its building codes without compromising resident safety, it provides a blueprint for other high-cost, high-density cities—such as San Francisco, New York, and Boston—to follow suit.
The broader implication here is a shift in the philosophy of urban planning. For decades, the default response to housing shortages was "build more." That led to sprawling suburban developments and massive, high-cost towers. Today, the focus is shifting toward "build better"—optimizing the capacity of existing land through technical innovation rather than just raw volume.
By proving that building codes can be modernized without sacrificing safety, Washington is challenging the rest of the country to stop treating codes as immutable laws of nature and start treating them as tools that can be refined to meet the urgent needs of the 21st-century city. As the state moves toward the 2027 implementation deadline, the eyes of urban planners across the country will be on Washington, waiting to see if this "unglamorous" change in stairwell design becomes the next big thing in the fight for affordable housing.
Ultimately, the scissor stair reform serves as a reminder that housing policy is a holistic endeavor. Zoning may set the stage, but it is the granular, technical details of the building code that determine whether that stage is ever actually built upon. By unlocking the "hidden" potential of narrow urban lots, Washington is demonstrating that sometimes the biggest solutions to the housing crisis are found in the most overlooked places.
