Illegal conversion

An illegal conversion is the use or configuration of a building outside what its certificate of occupancy and zoning permit — more dwelling units than certified, dwellings where none are allowed, cellar or attic occupancies the codes forbid. The pattern ranges from a single added unit to systematically subdivided buildings, and the enforcement responses range from violations to vacate orders where configurations endanger occupants.

For analysis, conversion risk reads from mismatches: unit counts in listings or utility patterns exceeding the certificate, layouts inconsistent with filed plans. The stakes are more than fines — illegally configured space can be uninsurable, unfinanceable, and, in the worst cases, unsafe in exactly the ways the occupancy rules exist to prevent.