All open parking areas of 36 or more parking spaces or at least 12,000 square feet in area shall provide at least one tree for every eight parking spaces. Fractions equal to or greater than one-half resulting from this calculation shall be considered to be one tree. Such trees shall be in addition to the trees required in the perimeter screening area. Each such tree shall have a minimum caliper of three inches and be located in a planting island with a minimum area of 150 square feet of pervious surface.
The following distribution rules shall apply:
(1) Each end space in a row of five or more parking spaces shall fully abut a planting island or a perimeter landscaped area along the long dimension of such end space;
(2) No more than 15 parking spaces shall be permitted between planting islands, or a planting island and a perimeter landscaped area; and
(3) For open parking areas at least 150,000 square feet in area, in addition to the requirements set forth in paragraphs (a)(1) and (a)(2) of this Section, every other row of parking spaces in which each space does not fully abut a perimeter landscaped area shall abut a planting island. Such planting island shall have a minimum width of eight feet and extend along the entire length of such row of parking spaces. Such planting islands may be traversed by walkways no more than three feet wide and spaced at least 50 feet apart.
(4) Planting islands required pursuant to paragraphs (a)(1) and (a)(3) may be discontinued where a pedestrian access lane is provided that serves no more than five parking spaces required by the Americans with Disabilities Act.
(5) Compliance with paragraphs (a)(1) and (a)(2) may be waived where the Commissioner of Buildings determines that tree planting in such locations would conflict with loading operations. Such trees shall be planted elsewhere in the open parking area.
(b) Grading, drainage and soil
The open parking area shall be graded to allow stormwater runoff to drain into all planting islands required pursuant to this Section and perimeter landscaped areas required pursuant to Section 37-921. Planting islands shall have an inverted slope to allow a minimum six inches and a maximum of one foot of stormwater ponding, and surface ponding must drain in at least 24 hours. To allow for adequate drainage, elevated catchbasins shall be placed in the planting island above the ponding level. Planting islands shall be comprised of soil with a depth of at least two feet, six inches, measured from the surface of the adjoining open parking area. Beneath such soil, filter fabric and one foot of gravel shall be provided. Proper drainage rates shall be attained through underdrains that are connected to detention storage that meets the drainage and flow requirements of the Department of Environmental Protection or through infiltration through the surrounding soil volume. If underdrains are not provided, soil boring tests shall be conducted by a licensed engineer to ensure that ponded surface water is drained in at least 24 hours. A raised curb shall edge the planting island, shall be at least six inches in height and shall contain inlets at appropriate intervals to allow stormwater infiltration from the open parking area.
However, where the Commissioner of Buildings determines that due to the natural sloping topography of the site the drainage provisions of this paragraph, (b), would be infeasible for an interior planting island, such drainage provisions may be waived. In lieu thereof, such planting island shall be comprised of soil with a depth of at least three feet measured from the adjoining open parking area. A raised curb shall edge the perimeter landscaped area and be at least six inches in height. The planting requirements of paragraph (c) of this Section shall apply to such planting islands, except that plantings need not be selected from the lists in Section 37-963.
The first two feet of the planting island fronting the open parking area shall be comprised of mulch and densely planted with groundcover above jute mesh to stabilize the inverted slope. This area may be used as an automobile bumper overhang area and may be included in calculating the required depth of an abutting parking space. The remaining area of the planting island shall be densely planted with shrubs, maintained at a maximum height of three feet, at a distance of 24 inches on center. Planting islands which are bisected by pedestrian access lanes serving Americans with Disabilities Act parking spaces (as shown in paragraph (a)(4) of this Section) shall provide groundcover in lieu of shrubs. Each required tree shall be centered in a planted area measuring at least eight feet by eight feet. Multiple trees are allowed in a single planting island provided they are spaced no closer than 25 feet on center and there is at least 150 square feet of pervious area for each tree. Any area with a dimension of less than two feet shall not contribute to such 150 square foot minimum area. Required trees shall be located first in planting islands at the ends of parking rows required pursuant to paragraph (a)(1) of this Section, and then in planting islands that break up parking rows with more than 15 spaces required pursuant to paragraph (a)(2) of this Section. Any remaining required trees may be located in the continuous planting island required pursuant to paragraph (a)(3) of this Section or located in other planting islands within the open parking area. All required trees, shrubs and groundcovers shall be selected from the lists in Sections 37-962 and 37-963.