Generally. No exterior alteration, restoration, reconstruction, demolition, new construction, or moving of a landmark or property within an historic district, nor shall any material change in the appearance of such property, its light fixtures, signs, sidewalks, fences, stops, paving, or other exterior elements visible from a public street or alley which affect the appearance and cohesiveness of the historic district, without first obtaining a certificate of appropriateness from the Scenic and Historic Preservation Commission.