In its most basic form, a nonconforming use is the use of a property which is no longer a permitted use under current zoning regulations but was permitted under prior zoning (or, in some cases, before there was zoning). In effect, a prior permitted use is grandfathered in despite the current zoning status. For instance, imagine the neighborhood where you run a business is rezoned as a residential area. Does this mean you have to shut your doors? No. Non-conforming uses play a key role in real estate development as a creative solution to promote urban infill through reuse of existing properties, as it may allow a use that is not otherwise permissible

There are two catches to non-conforming uses. The first catch is that the non-conforming use cannot substantially change the nature of the use in a more intense fashion. For instance, if an office building as non-conforming use has ten stories, the owner of the building cannot add two more stories to the building. The non-conforming use must be of the same type and intensity. The building owner could likely remove two stories from the building, making it an eight-story building. Once the building has been reduced, however, the building owner cannot then build two stories back on to the building, making it a ten-story building again. Once the non-conforming use has been reduced, it cannot be expanded again back to prior form.  In other words, non-conforming uses are a one-way street – you can stay where you are or de-intensify, but you can never expand.

The second catch is that the non-conforming use typically must be continuous. In Lexington, Kentucky, for instance, if a non-conforming use is discontinued for a year or more, the non-conforming use may not be resumed. If the non-conforming use becomes a permitted use, it cannot then revert to a non-conforming use.

The practical upshot of non-conforming use is that land use attorneys can help businesses identify properties with non-conforming uses that are ripe for reuse. For instance, a legal non-conforming restaurant may find new life from a new proprietor, and the practical effect of the updated zoning precludes other restaurants from setting up shop in the immediate area. Non-conforming use is a practical and creative way to give new life to existing structures even after zoning regulations change.