In all Residence Districts, except as provided in Section 23-621 (Permitted obstructions in certain districts), the obstructions listed in paragraphs (a) through (r) in this Section shall be permitted to penetrate a maximum height limit or sky exposure plane set forth in Sections 23-63 (Height and Setback Requirements in R1 Through R5 Districts), 23-64 (Basic Height and Setback Requirements), 23-66 (Height and Setback Requirements for Quality Housing Buildings) or 23-69 (Special Height Limitations):

(a)        Awnings and other sun control devices, provided that when located at a level higher than the first story, excluding a basement, all such awnings and other sun control devices:

(1)        shall be limited to a maximum projection from a building wall of 2 feet, 6 inches, except when located on the first story above a setback;

(2)        shall have solid surfaces that, in aggregate, cover an area no more than 30 percent of the area of the building wall (as viewed in elevation) from which they project; and

(3)        may rise above the permitted building height, up to the height of a parapet wall or guardrail permitted in accordance with paragraph (j) of this Section.

When located on the first story above a setback, awnings and other sun control devices shall be limited to a projection of 50 percent of the depth of the required setback, and shall be limited, in total, to 50 percent of the width of the building wall from which they project;

(b)        Balconies, unenclosed, subject to the provisions of Section 23-13;

(c)        Building columns, having an aggregate width equal to not more than 20 percent of the aggregate width of street walls of a building, to a depth not exceeding 12 inches, in an initial setback distance, optional front open area, or any other required setback distance or open area set forth in Sections 23-63, 23-64, 23-65 (Tower Regulations) or 23-66;

(d)        Chimneys or flues, with a total width not exceeding 10 percent of the aggregate width of street walls of a building at any level;

(e)        Decks, and other surfaces for recreational activities, not more than 3 feet, 6 inches in height, as measured from the maximum height limit, or the finished level of the roof as it existed on April 30, 2012, whichever is higher;

(f)        Dormers having an aggregate width of street walls equal to not more than 50 percent of the width of the street wall of a detached or semi-detached single- or two-family residence;

(g)        Elevator or stair bulkheads (including shafts; and vestibules not larger than 60 square feet in area providing access to a roof), roof water tanks and accessory mechanical equipment (including enclosures), other than solar or wind energy systems, provided that:

(1)        such obstructions shall be located not less than 10 feet from the street wall of a building, except that such obstructions need not be set back more than 25 feet from a narrow street line or more than 20 feet from a wide street line. However, such restrictions on location shall not apply to elevator or stair bulkheads (including shafts or vestibules), provided the aggregate width of street walls of such bulkheads within 10 feet of a street wall, facing each street frontage, times their average height, in feet, does not exceed an area equal to four times the width, in feet, of the street wall of the building facing such frontage;

(2)        all mechanical equipment shall be screened on all sides;

(3)        such obstructions and screening are contained within a volume that complies with one of the following:

(i)        the product, in square feet, of the aggregate width of street walls of such obstructions facing each street frontage, times their average height, shall not exceed an area equal to eight feet times the width, in feet, of the street wall of the building facing such frontage; or

(ii)        the lot coverage of all such obstructions does not exceed 20 percent of the lot coverage of the building, and where the maximum permitted height of a building is less than 120 feet, such obstructions are limited to a maximum height of 25 feet, and where the maximum permitted height of a building is 120 feet or greater, such obstructions are limited to a maximum height of 40 feet.

For the purposes of this paragraph, (g), abutting buildings on a single zoning lot may be considered to be a single building;

(h)        Exterior wall thickness, up to eight inches, where such wall thickness is added to the exterior face of a building wall existing on April 30, 2012, provided the added wall thickness has a thermal resistance (R-value) of at least 1.5 per inch. Where buildings that have added exterior wall thickness pursuant to this Section are enlarged, such enlarged portion may similarly penetrate a maximum height limit in order to align with the exterior walls of the existing building, provided such enlargement contains less floor area than the existing building, and there is no penetration of floor area above a maximum height limit;

(i)        Flagpoles or aerials;

(j)        Parapet walls, not more than four feet in height, as measured from the maximum height limit, or the finished level of the roof as it existed on April 30, 2012, whichever is higher. A guardrail with a surface at least 70 percent open or with an opacity no more than 30 percent (as viewed in elevation), shall be permitted above a parapet wall or within two feet of a parapet wall, provided such guardrail is not more than four feet above the accessible level of a roof. Such restriction on guardrail height shall not apply when located beyond two feet from a parapet wall;

(k)        Roof thickness, up to eight inches, to accommodate the addition of insulation, for buildings or portions of buildings constructed prior to April 30, 2012. For a building that has added roof thickness pursuant to this paragraph, an enlargement may align with the finished roof surface of such building, provided the enlarged portion does not exceed the maximum height limit by more than eight inches;

(l)        Skylights, clerestories or other daylighting devices, not more than four feet in height, as measured from the maximum height limit, or the finished level of the roof as it existed on April 30, 2012, whichever is higher. Such devices shall be limited to a lot coverage not greater than 10 percent of the lot coverage of the roof and be located at least eight feet from the street wall edge. However, such devices shall not be permitted obstructions above a roof with a slope greater than 20 degrees;

(m)        Solar energy systems:

(1)        on the roof of a building, up to four feet in height, as measured from the maximum height limit, or the finished level of the roof, whichever is higher;

(2)        on the roof of a building, greater than four feet in height, as measured from the maximum height limit, or the finished level of the roof, whichever is higher, provided that all such portions above four feet are set back at least six feet from a street wall, limited to a lot coverage not greater than 25 percent of the lot coverage of the roof and do not exceed:

(i)         in R1 through R5 Districts, a height of six feet;

(ii)        in R6 through R10 Districts, a height of 15 feet; and

(iii)        when located on a bulkhead or other obstruction pursuant to paragraph (g) of this Section, a height of six feet;

(3)        on walls existing on April 30, 2012, projecting no more than 10 inches and occupying no more than 20 percent of the surface area of the building wall (as viewed in elevation) from which it projects.

However, any installation on a roof with a slope greater than 20 degrees shall be limited to 18 inches in height, as measured perpendicular to the roof surface.

(n)        Vegetated roofs, not more than 3 feet, 6 inches in height, excluding vegetation, as measured from the maximum height limit, or the finished level of the roof as it existed on April 30, 2012, whichever is higher. On roofs with slopes greater than 20 degrees, vegetated roofs shall be limited to a height of 12 inches measured perpendicular to such roof surface;

(o)        Weirs, check dams and other equipment for stormwater management, not more than 3 feet, 6 inches in height, as measured from the maximum height limit, or the finished level of the roof as it existed on April 30, 2012, whichever is higher;

(p)        Wind energy systems on portions of buildings with a height of 100 feet or greater, provided:

(1)        the highest point of the wind turbine assembly does not exceed 55 feet;

(2)        no portion of the wind turbine assembly is closer than 10 feet to any lot line; and

(3)        the diameter of the swept area of the rotor does not exceed 15 feet;

(q)        Window washing equipment mounted on a roof;

(r)        Wire, chain link or other transparent fences.