Is my house historic?

It depends.

Houses in historic overlays either "contribute" to the historic character of the neighborhood, or they do not.

Generally, houses built before or during World War 2 are considered to be contributing because of their age.  However, not every house built before 1945 is necessarily contributing, as a house that has been so significantly modified that it has bears little resemblance to its original appearance have in effect become non-contributing. 

In addition to the age of a house, the presence of a recognizable architectural style often indicates that a structure is contributing to the historic character of a neighborhood.  The Historical Commission has developed some useful resources to help you identify the style of your home: http://www.nashville.gov/Historical-Commission/Educational-Resources/Publications-and-Brochures.aspx.

Also, it is possible that a house built after 1945 is contributing because it reflects an important period or style of architecture, is the work of a significant designer or builder, or is associated with an important person or event.  Other factors could also affect whether or not a property is contributing or not.