In R6 through R10 Districts without a letter suffix, the obstructions permitted for any yard set forth in paragraph (a) of Section 23-311 (Permitted obstructions in all yards, courts and open areas), as well as the following obstructions, shall be permitted in any open space required on a zoning lot. For the purposes of applying such allowances to open space, all percentage calculations shall be applied to the area of the open space instead of the yard:

1. balconies, unenclosed, subject to the provisions of Section 23-62;
2. breezeways;
3. driveways, private streets, open accessory off-street parking spaces, unenclosed accessory bicycle parking spaces or open accessory off-street loading berths, provided that the total area occupied by all these items does not exceed 50 percent of the required open space on any zoning lot;
4. energy infrastructure equipment and accessory mechanical equipment, subject to the requirements set forth in Section 23-312 (Additional permitted obstructions generally permitted in all yards);
5. greenhouses, non-commercial, accessory, limited to one story or 15 feet in height above adjoining grade, whichever is less, and limited to an area not exceeding 25 percent of the open space#;
6. parking spaces, off-street, enclosed, accessory, provided that the total area occupied by a building used for such purposes does not exceed 20 percent of the total required open space on the zoning lot;
7. solar energy systems:
   1. on the roof of an accessory building, limited to 18 inches in height as measured perpendicular to the roof surface; or
   2. affixed to solar canopies and located over any accessory off-street parking space, provided that the height shall not exceed 15 feet above the level of the adjoining grade;
8. steps;
9. swimming pools, accessory, above-grade structures limited to a height not exceeding eight feet above the level of the rear yard or rear yard equivalent; or
10. fire escapes or planting boxes, provided that no such items project more than six feet into or over such open space.

However, any such open space that is part of a required yard, rear yard equivalent or court may contain an obstruction listed in this Section only where such obstruction is permitted, pursuant to Sections 23-311, 23-312, 23-341 (Permitted obstructions in required rear yards or rear yard equivalents) or 23-351 (Permitted obstructions in courts), as applicable.