The Mayor's Agent rules on the basis of specific criteria stated in the DC historic preservation law. To approve an application for permit or subdivision, the Mayor's Agent must find that approval was necessary in the public interest, or that failure to approve the application would result in unreasonable economic hardship to the owner.

Necessary in the public interest  means consistent with the purposes of the preservation law, or necessary to allow the construction of a project of special merit.

Special merit means that a project provides significant benefits to the District or to the community by virtue of exemplary architecture, specific features of land planning, or social or other benefits having a high priority for community services.

Unreasonable economic hardship means that the failure to issue a permit would amount to a taking of the owner's property without just compensation, or in the case of a low-income owner, would impose an onerous and excessive financial burden.

Purposes of the DC historic preservation law are:  

With respect to historic districts:

• To retain and enhance those properties which contribute to the character of the historic district and to encourage their adaptation for current use;
• To assure that alterations of existing structures are compatible with the character of the historic district; and
• To assure that new construction and subdivision of lots in an historic district are compatible with the character of the historic district; 

With respect to historic landmarks

• To retain and enhance historic landmarks in the District of Columbia and to encourage their adaptation for current use; and
• To encourage the restoration of historic landmarks.

With respect to designated archaeological sites:

• To protect historic and prehistoric archaeological sites from irreparable loss or destruction; and
• To encourage the retrieval of archaeological information and artifacts when the destruction of an archaeological site is necessary in the public interest.