Buffer strip. There shall be a buffer strip of at least 10 feet, located within the townhouse property, between this zone district and any property used or zoned for residential purposes, except that on the eastern boundary of this zone district, the buffer strip shall be at least five feet. This strip shall be landscaped and planted with evergreens at least six feet in height throughout its entire length and shall be so maintained. This planting shall be so located with sufficient density as to screen from view any building located on said plot from any contiguous residential zone district and shall be subject to the approval of the Planning Board. Any existing growth in such buffer strip shall be preserved if such existing growth supplements the desired screening effect. The buffer strip area may be crossed by driveways and access roadways. The buffer strip may be coincidental with and include any other setback requirements.