Parking areas, roads, house sites, other impervious surfaces and their improvements shall not be included in the calculation to determine the amount of available open space. However, the entire tract, apart from these exceptions, shall be considered in determining the required amount of open space. The following facilities or improvements may be located on open space land: stormwater systems, bike paths, walking trails and other common community facilities that do not involve buildings or imperviousness, such as playgrounds.