36 C.F.R. § 51.64
A concessioner that, with the written approval of the Director, undertakes a major rehabilitation or adds a new structure ( e.g., a new wing to an existing building or an extension of an existing sidewalk) to an existing structure in which the concessioner has a leasehold surrender interest, will increase its leasehold surrender interest in the related structure, effective as of the date of substantial completion of the major rehabilitation or new structure, by the construction cost of the major rehabilitation or new structure. The Consumer Price Index adjustment for leasehold surrender interest value purposes will apply to the construction cost as of the date of substantial completion of the major rehabilitation or new structure. Approvals for major rehabilitations and additions to structures are subject to the same requirements and conditions applicable to new construction as described in this part.
36 C.F.R. § 51.64