Properties located within a designated historic district are subject to design review. Property owners proposing to make a "material change in appearance" to a property within the district are required to apply for a Certificate of Appropriateness from the Historic Preservation Commission before making any changes. The Commission is required to grant a Certificate unless it can justify not doing so. Certificate of appropriateness (COA) is defined as "a document evidencing approval by the Historic Preservation Commission of an application to make material change in the appearance of a designated historic property or of a property located within a designated historic district." The ordinance defines a material change in appearance as follows: "a change that will affect either the exterior architectural or environmental features of a historic property or any building, site, object, landscape feature or work of art within a historic district such as:
- A reconstruction or alteration of the size, shape or facade of a historic property, including relocation of any doors or windows or removal or alteration of any architectural features, details or elements;
- Demolition or relocation of a historic structure;
- Commencement of excavation for construction purposes;
- A change in the location of advertising visible from the public right-of-way; or
- The erection, alteration, restoration or removal of any building or other structure within a historic property or district, including walls, fences, steps and pavements, or other appurtenant features."
Ordinary maintenance or repair of any exterior architectural feature, that does not involve a material change in design, material, or outer appearance, is excluded from review. Also, interior changes to properties that do not have an effect on exterior appearance are also excluded from review.