In his ambitious recent citywide Block by Block housing program, Mayor Mamdani pledged to “expand opportunities for homeowners to add accessory dwelling units and legalize basement apartments safely.”

Mamdani may think he’s a housing pathbreaker — but he’s echoing both his two immediate predecessors. In 2019, Bill de Blasio said “there are thousands of basement apartments in our city, but too many are illegal and unsafe.”

In 2025, Eric Adams decried the fact that “too many New Yorkers have been forced into dangerous basement and cellar set-ups just to find a place to live” and pledged to turn illegal, unsafe apartments into “legal, safe ones.”

Perhaps Mamdani will be more successful in this mission — but there’s a reason that so many dangerous basement units continue to exist: the city’s requirements to make them legal are too stringent and therefore too costly.

To make a basement unit comply with city building codes, not........

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