Simply put, the historic districts hold more contributing properties than non-contributing. And contributing buildings were built before 1945. For more information about what makes a house contributing and other standards used by the National Register of Historic Places, see Yvette Yescas’ five-part series, linked at the bottom.
Reminder: as part of the historic district, homeowners do not have additional responsibilities or requirements when it comes to renovation or fixes to their property. However, if you’d like to maintain the historic integrity of your home during alterations, Yvette Yescas’ series talks about that, in addition to discussing what qualifies a home as a contributing property. Links: