Integrity is based on significance: why, where, and when a property is important. Only after significance is fully established can you proceed to the issue of integrity.
The steps in assessing integrity are:
- Define the essential physical features that must be present for a property to represent its significance.
- Determine whether the essential physical features are visible enough to convey their significance.
- Determine whether the property needs to be compared with similar properties. And,
- Determine, based on the significance and essential physical features, which aspects of integrity are particularly vital to the property being nominated and if they are present.
Ultimately, the question of integrity is answered by whether or not the property retains the identity for which it is significant.
All properties change over time. It is not necessary for a property to retain all its historic physical features or characteristics. The property must retain, however, the essential physical features that enable it to convey its historic identity. The essential physical features are those features that define both why a property is significant (Applicable Criteria – see below, and Areas of Significance) and when it was significant (Periods of Significance). They are the features without which a property can no longer be identified as, for instance, a late 19th century dairy barn or an early 20th century commercial district.
Four Criteria for Evaluating Significance
CRITERION A: EVENT: Properties can be eligible for the National Register if they are associated with events that have made a significant contribution to the broad patterns of our history.
CRITERION B: PERSON: Properties may be eligible for the National Register if they are associated with the lives of persons significant in our past.
CRITERION C: DESIGN/CONSTRUCTION: Properties may be eligible for the National Register if they embody the distinctive characteristics of a type, period, or method of construction, or that represent the work of a master, or that possess high artistic values, or that represent a significant and distinguishable entity whose components may lack individual distinction.
CRITERION D: INFORMATION POTENTIAL: Properties may be eligible for the National Register if they have yielded, or may be likely to yield, information important in prehistory or history.
[National Register Bulletin 15]