In both Business Districts A and B, in the event of the construction, reconstruction or substantial alteration of any building or structure that is used, or intended to be used, in whole or in part, for any industry, trade, manufacturing or commercial purpose, there shall be constructed as part of such construction, reconstruction or substantial alteration a raised granite curb at least six inches in height along the edge of the street, except at approved driveway openings. There also shall be a paved pedestrian sidewalk no less than five feet in width set back no less than four feet from the street lot line for the entire length of the lot frontage; provided however, where driveways exist, the sidewalk shall be separated from the remainder of the lot with a strip four feet wide in which suitable evergreen shrubs or other landscaping approved by the ZBA shall be maintained in good condition. The strip between the sidewalk and the street shall be maintained in good condition as a grass area. The sidewalk location shall be such as to join in a reasonable manner existing or planned sidewalks on abutting land.