Federal and state permitting requirements typically include a review of historic resources, 50 years of age or older, to determine if resources within the APE may be eligible for listing in the NRHP and if they would be affected by the proposed undertaking. In addition, architectural historians can examine the evolution of a building over time, particularly one that has had several past lives, each of which may have historic significance, in order to inform decisions about preservation and restoration. 

Such resources may include houses, barns, hangers, office buildings, roads, air strips, rocket launch pads, cemeteries, wells, and gardens. Architectural historians examine all aspects of the built environment, identifying the types of resources present, their relation to one another, and evaluating the level of integrity. Information is collected about original function, uses, changes over time, and owners’ and/or designers’/architects’ history. The significance of a historic resource is evaluated using the NRHP criteria and if enough cultural resources are found that possess a significant concentration, linkage, or continuity united historically or aesthetically by plan or physical development, a group/area can be designated a historic district.

While examining historic resources an architectural historian will photograph the exterior, take measurements as needed, describe and analyze the architectural features, and conduct background research.