43 C.F.R. § 17.260
(a) Definitions. For the purposes of this section, Historic Preservation Programs are those that receive Federal financial assistance that has preservation of historic properties as a primary purpose.
Historic properties means those buildings or facilities that are listed or eligible for listing in the National Register of Historic Places, or such properties designated as historic under a statute of the appropriate State or local governmental body.
Substantial impairment means a permanent alteration that results in a significant loss of the integrity of finished materials, design quality or special character.
(b) Obligations.
(1) A recipient shall operate any program or activity involving Historic Preservation Programs so that when each part is viewed in its entirety it is readily accessible to and usable by handicapped persons. This paragraph does not necessarily require a recipient to make each of its existing historic properties or every part of an historic property accessible to and usable by qualified handicapped persons. Methods of achieving accessibility include:
(iv) Adopting other innovative methods to achieve accessibility.
Because the primary benefit of an Historic Preservation Program is the experience of the historic property itself, in taking steps to achieve accessibility, recipients shall give priority to those means which make the historic property, or portions thereof, physically accessible to handicapped individuals.
(2) Where accessibility cannot be achieved without causing a substantial impairment of significant historic features, the Secretary may grant a waiver of the accessibility requirement. In determining whether accessibility can be achieved without causing a substantial impairment, the Secretary shall consider the following factors:
(iv) Cost of alterations in comparison to the increase in accessibility.
The Secretary shall periodically review any waiver granted under this section and may withdraw it if technological advances or other changes so warrant.
[47 FR 29546, July 7, 1982, as amended at 55 FR 28912, July 16, 1990; 68 FR 51377, Aug. 26, 2003]