D.C. Mun. Regs. tit. 11, r. 11-D1009
Buildings constructed on or before April 17, 1992, and existing legitimate uses within the buildings shall be deemed conforming, except that no addition, replacement, or expansion of the building, or change in use (except to a more conforming residential use other than a dormitory) shall be permitted unless in conformance with the requirements of the R-17 zone.
If any building is destroyed by fire, collapse, explosion, or act of God, it may be reconstructed or restored to its previous condition or to a more conforming residential condition other than a dormitory. Excluded from this provision are uses that are nonconforming prior to April 17, 1992, and operating without a special exception issued by the Board of Zoning Adjustment.
D.C. Mun. Regs. tit. 11, r. 11-D1009