D.C. Mun. Regs. tit. 10, r. 10-C701
Historic districts and landmarks are identifiable entities that possess and convey historic significance as a whole. To meet the integrity requirement for designation, the preponderance of buildings and structures comprising a district or landmark shall contribute to its historic significance. Most districts nonetheless contain some buildings or structures that do not contribute to the significance of the district. Some landmark sites may also include buildings or structures that do not contribute to the significance of the landmark.
A building or structure shall be evaluated by comparison with the established historic significance and physical attributes of the overall district or landmark. The determination of whether a building or structure contributes to historic significance shall be based on information such as date of construction, function, associations, and physical characteristics. The determination for an archaeological site shall be based on an analysis of the information potential of the component element.
An addition to a historic building, particularly an addition that is largely self-contained, may be evaluated separately for a determination of significance. An integral element of a building or structure shall not be evaluated separately for this purpose.
A contributing or non-contributing determination made at the time of a historic district or historic landmark designation shall be presumed to retain validity unless a re-evaluation is warranted due to physical change, the availability of new information, or the passage of time since the designation was made.
D.C. Mun. Regs. tit. 10, r. 10-C701