In an office building in downtown Manhattan, an eight-foot-long banner stretched across the length of a fluorescent-lit hallway.

Five-inch-tall red letters indicated the location of an entrance to a basement apartment, as required outside each unit. That’s according to proposed rules from the Department of Buildings for a pilot program to legalize those illicit spaces.

The rules specify both the color and five-inch height of the letters on the sign.

The requirement is “cartoonishly absurd,” said Howard Slatkin, executive director of the Citizens Housing and Planning Council, which commissioned the large banner’s creation.

It’s one of several such measures in the proposed rules from the Department of Buildings that safe housing advocates say impose obstacles or make it untenable for h

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