Nothing in this chapter shall be construed to prevent the ordinary maintenance and repair of any exterior architectural feature of a landmark or property within an Historic Preservation Overlay District that does not involve a change in design, material or outward appearance. No person shall carry out any exterior alteration, restoration, reconstruction, demolition, new construction, or moving of a landmark or property within an Historic Preservation Overlay District, nor shall any person make any material change in the appearance of such property, its windows and shutters, exterior light fixtures, signs, sidewalks, fences, steps, paving, changes in grade, or other exterior elements which affect the appearance and cohesiveness of the landmark or Historic Preservation Overlay District, without first obtaining a certificate of appropriateness from the Historic Preservation Board.