Common open spaces, such as parks, preserves, recreation areas and facilities, tennis courts, golf courses, lakes, ponds, playgrounds, swimming facilities, drainage or other ways and other similar uses, along with structures and accessory features appurtenant thereto, shall be provided at a ratio of not less than 40% of the gross area of the planned unit residential development. The types and amounts of areas to be counted toward establishing the minimum amount of common open space shall be determined by the Planning Board but shall not include areas designated as sidewalks, roads, drives, paved parking areas, required front yards and those side yards as established by the Planning Board along side lot lines. The Planning Board may require such areas to be considered as part of the common open space for maintenance and other purposes, even though such areas are not of the type to be counted toward establishing the 40% minimum area.