Since this comes up a lot in waterfront purchases, let's use a real world example. Boathouses are the crown jewel up here in the lakes region. (Here are some Boathouses on Lake Winnipesaukee!) If you are purchasing a property with a boathouse, you must be satisfied about one of two criteria.

First, if the structure can be proven to exist without alteration, prior to July 2, 1969, then it is most likely "grandfathered"**. Second, if the construction happened after July 2, 1969 and permits can be produced to show the structure in its current location, size and configuration, then it's also most likely "grandfathered".**

Grandfathered structures can be maintained, but in most cases have to be kept in the same place without altering the structure's size or configuration**.  Be careful of boathouses that may have grown over time or suddenly have finished space that was not permitted.