Washington state continues to lead the pack with measures to lower the cost of homebuilding and make it easier to build more homes, in all shapes and sizes, in more places. The state reformed building codes to allow single-stair apartments in 2023, to extend residential code to middle housing in 2024, and in 2026, to legalize smaller elevators, as well as—the focus of this article—scissor stairs.1

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Scissor stairs are a design feature common in other countries but rare in most US cities. 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. What’s more, scissor stairs make it possible to design for more light and cross-breeze in every apartment, plus accommodate narrow or oddly shaped lots for more infill opportunities.

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Scissor stairs increase the efficiency of circulation by arranging two separate stairways in one compact, interlocking coil like a double helix. The interlocking stairways have separate exits on each floor. They are enclosed and separated by fire-resistance-rated walls (see diagram below). The stairwells in a scissor stair never cross or intermingle with one another, and their walls ensure that if one stairway is compromised with smoke or fire, residents and emergency responders can safely use the other one.

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Scissor stairs yield a compact building core that holds stairs, elevators, and hallways. As shown below, less space for the core means more space for living. And the slimmer the building, the more important it is to minimize the size of the core, to keep it from consuming an ever larger portion of the leasable floorspace. In other words, scissor stairs make small footprint designs more financially feasible to build.

Building data from Los Angeles, Seattle, and Vancouver, BC, illustrate the efficiency gains possible with scissor stairs (see summary table below and appendix for complete data set). The average core area for circulation (stairs and hallways, but not elevator hoistways) in Vancouver’s scissor stair buildings is 46 percent smaller than the average in Seattle’s separate-stair buildings and 56 percent smaller than Los Angeles’. The floor plates of Vancouver highrises typically range from 6,000 to 8,000 square feet, while in Seattle and LA, it’s 10,000 to 12,000 square feet.

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Scissor stairs also offer benefits beyond raw floor-space efficiency. First, the smaller-footprint buildings they facilitate can fit on smaller lots, making more infill housing possible, reducing land costs, and obviating the onerous process of assembling multiple parcels often needed to hold large buildings.

Second, skinnier buildings yield homes with better natural light and ventilation. That’s because less of the living space is far from the windows, and more of the homes are likely to include corners of the building, allowing for windows on two sides. Skinnier buildings can also leave more space between neighboring buildings, which can improve views for tenants and neighbors passing by.

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Countries throughout the world commonly allow scissor stairs, as in Hong Kong and China, for example.2 For over 30 years, builders in Canada, and especially in Vancouver, British Columbia, and Toronto, Ontario, have routinely used scissor stairs in residential towers to help create their exemplary urban neighborhoods near transit and amenities.

In contrast, scissor stair buildings are far less common in most US cities, though scattered examples can be found throughout the country, built as far back as the 1950s. Since then, building code changes adopted across most of the US now prohibit scissor stairs, though the timeline varies.3 In Western states, including Washington, building codes have effectively banned scissor stairs since the early 1970s (page 406, 1967 and page 472, 1973). Code requires stairway doors to be separated by a distance of at least one-half the diagonal dimension of the building, making it impossible to use an interlocking configuration.

The two current US exceptions are New York City and Dallas. New York City continued to allow scissor stairs in residential buildings, opting to not follow the national trend new stair separation restrictions. New York City even allows scissor stairs in office buildings no taller than six stories (between 1968 and 2008, that allowance had no height limit; page 228, 27-363).