Not all old buildings are classified the same! Old buildings can be broken into two categories: Historic Buildings and Existing Buildings.
Historic buildings are listed on a local, state, or national historic registers and are typically at least 50 years old. Existing buildings are – potentially historic - buildings that aren’t listed on a local, state, or national register even if they are at least 50 years old. Just because an existing building is old does not mean it is historically listed. (In order for a building to be listed on a local or national level someone must have successfully completed the nomination process through the State Historic Preservation Office.) Potentially Historic Buildings are typically less than 50 years old and with each passing day get closer to being eligible for listing on a historic register.
Preservation designations listed from least restrictive to most restrictive preservation protections:
1. National Historic Landmark
2. State, City, or local Landmark
3. National Register Individual listing
Although, counterintuitive, buildings that are listed on a local or state historic register typically have to go through a more stringent review process than buildings that are on the National Register.