Scissor stairs may lower Washington multifamily building costs

Zoning reform has grabbed most of the attention in housing policy circles, but sometimes it’s the unglamorous, technical building code changes that save builders real money.

Single-stair reform was the first to sweep through state legislatures and city halls as a tool to spur missing-middle housing. Washington state is now cutting deeper into the building code by allowing scissor stairs – two interlocking stairways that crisscross within a single, fire-rated enclosure.

Gov. Bob Ferguson quietly signed the building code change into law in March, making Washington the first state in the nation to allow scissor stairs in multifamily construction. The law takes effect June 11. Whether other states follow will depend on both the reform’s performance and the fire safety industry’s considerable influence over building code changes.

For Washington, the change is the latest in a steady flow of aggressive housing reform to address a severe affordability crisis. The crisis is concentrated in the Seattle metro area, where Amazon, Microsoft, and a dense tech corridor have made the region one of the most expensive housing markets in the country.

Single-stair code changes were among the laws passed. After three years of work, the State Building Code Council faces a July 1 deadline to adopt amendments allowing single-stair construction up to six stories. Seattle has allowed that type of construction for decades.

Single stair versus scissor stair

Single-stair reform targets smaller multifamily buildings, typically six stories or fewer with a dozen or so units, where one stairwell is sufficient for safe egress. Scissor stairs solve a different problem. In taller buildings on tight urban infill lots, placing two stairwells at opposite ends of the floor plate can consume so much of a narrow building’s width that development becomes impossible.

By folding two fire-rated egress paths into a single shared shaft, scissor stairs restore that lost design flexibility – opening urban lots that the dual-stairwell requirement had effectively locked out of development. Those separate shafts for dual stairwells also carve out significant floor area that could otherwise be leasable units. Developers can trim a building’s footprint, add units, or both.

“Scissor stairs are a design feature common in other countries but rare in most US cities,” Seattle urban planner Markus Johnson wrote in a post for think tank Sightline Institute. “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.”

Research suggests the design consolidation can cut total construction costs by 6% to 13% per building, even after accounting for additional fire protection requirements. For a mid-rise project in Seattle or Bellevue, that translates to hundreds of thousands of dollars left on the table under the old code.

Builders eager to take advantage of the new law will need to wait a little longer. It directs the State Building Code Council to convene an advisory committee and develop final code amendments – a rulemaking process expected to extend into 2027. June 11 opens the door, but the council will determine exactly how far.