The regulations contained herein relating to the height of buildings and the size of yards and other open spaces shall be subject to the following exceptions.
Chimneys, cooling towers, elevator bulkheads, fire towers, monuments, windmills, stacks, scenery lofts, tanks, water towers, ornamental towers, spires, wireless or broadcasting towers, masts or aerials and necessary mechanical appurtenances exceeding the height regulations of this chapter may be permitted as conditional uses by the Plan Commission.
The yard requirements stipulated elsewhere in this chapter may be modified as follows:
A. 
Uncovered stair restrictions. Uncovered stairs, landings and fire escapes may project into any yard, but not to exceed six feet and be not closer than three feet to any lot line, and must be eight feet or more above ground.
B. 
Cul-de-sac and curve restrictions. Residential lot frontage on culs-de-sac and curves in R-1 Districts may be less than 80 feet, provided the width at the building setback line is at least 80 feet and the street frontage is not less than 45 feet. Residential lot frontage on culs-de-sac and curves in R-2 Districts may be less than 100 feet, provided the width at the building setback line is at least 100 feet and the street frontage is not less than 55 feet.
C. 
Architectural projection restrictions. Architectural projections such as chimneys, flues, sills, eaves, belt courses and ornaments may project into any required yard, but such projection shall not exceed two feet.
D. 
Residential fence restrictions. Residential fences are permitted only on the rear and side yards in the residential districts and shall be located no closer than 18 inches from the property line. On the side yards, the fence shall not project into the principal building required setback distance and shall be in compliance with required vision clearance. A building permit is required; see Chapter 115, Building Construction, of the Code of the City of Markesan.
E. 
Security fence restrictions. Security fences are permitted on the property lines in all districts, but shall not exceed 10 feet in height and shall be an open type similar to woven-wire or wrought-iron fencing. A building permit is required. See Chapter 115, Building Construction, of the Code of the City of Markesan.
F. 
Essential services exemptions. Essential services, utilities, electric power and communication transmission lines are exempt from the yard and distance requirements of this chapter.
G. 
Street yard restrictions. With the approval of the Building Inspector, the required street yards may be decreased in any residential, business or industrial district to the average of the existing street yards of the abutting structures on each side, but in no case less than 15 feet in the residential districts and five feet in any business or industrial district.
Except in C-1 Districts, on corner lots, the side yard facing the street shall not be less than 30 feet.
Where a lot abuts on two or more streets or alleys having different average established grades, the higher of such grades shall control only for a depth of 120 feet from the line of the higher average established grade.
The requirements for a rear yard for buildings on through lots and extending from street to street may be waived by furnishing an equivalent open space on the same lot in lieu of the required rear yard, provided that the setback requirements on both streets be complied with.
Accessory buildings which are not a part of the main building shall not occupy more than 30% of the area of the required rear yard, shall not be more than 16 feet high and shall not be nearer than five feet to any lot line or five feet to any alley line, and shall not extend into a front yard beyond the required setback.
Every part of a required yard shall be open to the sky unobstructed except for accessory buildings in a rear yard, and the ordinary projections of sills, belt courses, cornices and ornamental features projecting not more than two feet.