D.C. Mun. Regs. tit. 9, r. 9-321
The Joint Committee on Landmarks of the National Capital (also referred to in this section as the "Joint Committee") shall, on or before December 15, 1975, provide the Mayor with a listing of all buildings which it has designated historic landmarks, and shall notify the Mayor on or before June 15th and December 15th of each succeeding year of any additions or deletions to that listing.
In order to be eligible for tax relief provided by D.C. Official Code § 47-842, owners of buildings which have been designated historic landmarks by the Joint Committee shall enter into an agreement with the Mayor for a period of not less than twenty (20) years to use and maintain the building in a manner which will assure the continued maintenance and preservation of the building as an historic site.
An eligible building for which the owner has entered into an agreement with the Mayor in accordance with § 321.2 shall, in addition to being assessed at full market value, be assessed, both as to land and improvements, as an historic site.
Assessment as an historic site, if it is less than the full market value determined without regard to the historic nature of the building, shall be the basis of tax liability in the District.
If the Deputy Chief Financial Officer determines that a building (or any part of it) for which an agreement has been entered into (in accordance with § 321.2) was not used and properly maintained in accordance with the agreement during all or any part of any fiscal year, that building (or part of a building) shall be assessed for the fiscal year (or part of fiscal year) on the basis of full market value.
The difference, if any, between the assessments made on the basis of full market value and assessments primarily made on the basis of the current use of the land and improvements shall be the basis of tax liability for violation of the agreement.
Any back taxes, plus interest at the prevailing U.S. Treasury Bill rate of interest for the fiscal year (or part of it) during which the terms of the agreement were not met, which may be due and owing shall be payable within sixty (60) days after the date of mailing by the Deputy Chief Financial Officer to the owner of a notice of the amount of taxes and interest due.
D.C. Mun. Regs. tit. 9, r. 9-321