It’s official: Colorado just became the latest state to legalize single-stair multifamily housing up to five stories.

Governor Jared Polis signed HB25-1273 into law yesterday, calling it a breakthrough for affordability and housing innovation. The bill requires cities like Denver to update their building codes by December 2027 to allow mid-rise residential buildings with just one staircase—so long as strict fire safety and ventilation standards are met.

This change may sound technical, but its impact could be significant. Under prior code, developers were required to include two stairwells in most buildings over three stories—resulting in inefficient layouts, higher construction costs, and fewer units. The new law unlocks the potential for more livable, space-efficient housing across Colorado.

Polis described the model as “smart-stair housing,” adding, “This will help meet housing demands across our state. More homes, lower costs.”

Colorado now joins other cities like Seattle and countries like Norway that have long allowed single-stair designs as a way to increase density without high-rises or displacement. As demand grows for walkable, transit-oriented neighborhoods, this shift opens the door for more flexible, design-forward development.

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