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In the districts indicated, the obstructions permitted for any yard set forth in paragraph (a) of Section 23-441 (General permitted obstruction allowances), 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 23-13;
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 the percentages set forth in Section 25-64 (Restrictions on Use of Open Space for Parking);
4. Energy infrastructure equipment and accessory mechanical equipment, subject to the requirements set forth in Section 23-442;
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, not to exceed one space per dwelling unit, when accessory to a single-family, two-family or three-family residence, 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. However, two such spaces for a single-family residence may be permitted in lower density growth management areas and in R1-2A Districts;
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;
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 23-44 (Permitted Obstructions in Required Yards or Rear Yard Equivalents) or 23-87 (Permitted Obstructions in Courts), as applicable.