Retaining walls not meeting the requirements of this section may be approved by the Board of Zoning Adjustment as a special exception pursuant to Subtitle X. In addition to meeting the general conditions for being granted a special exception as set forth in that subtitle, the applicant must demonstrate that conditions relating to the building, terrain, or surrounding area would to make full compliance unduly restrictive, prohibitively costly, or unreasonable.
D.C. Mun. Regs. tit. 11, r. 11-C1402