Open space requirements. A minimum of 30% of the parcel shown on the development plan shall be contiguous open space, excluding required yards and buffer areas. Such open space may be separated by the road(s) constructed within the townhouse development. Not more than 25% of such open space shall be wetlands, as defined pursuant to MGL c. 131, § 40. The required open space shall be used for conservation, historic preservation and education, outdoor education, recreation, park purposes, agriculture, horticulture, forestry, or for a combination of these uses, and shall be served by suitable access for such purposes. The required open space shall remain unbuilt upon, provided that 10% of such open space may be paved or built upon for structures accessory to the dedicated use or uses of such open space, pedestrian walks, and bike paths, and agriculture. Underground utilities to serve the townhouse development site may be located within the required open space.