“Of Exceptional Importance”: The Origins of the “Fifty-Year Rule” in Historic Preservation

The “fifty-year rule” is one of the most commonly accepted principles within American historic preservation: properties that have achieved significance within the past fifty years are generally not considered eligible for listing in the National Register of Historic places. An often misunderstood chronological threshold, the fifty-year standard was established by National Park Service historians in 1948. Until the advent of the “new preservation” with the National Historic Preservation Act in 1966, the standard of exceptional importance had only been applied to presidential and atomic heritage sites. Operating as a filter to ward off potentially controversial decisions about the nature of historic site significance, understanding the origins of the fifty-year rule reveals how Americans have constructed the chronological boundaries of a useable past through historic preservation during the twentieth century.