The Supplemental Site Development Regulations recognize the existence of special conditions that cannot comply literally with the site development regulations set out for each zoning district. Therefore, these regulations qualify or modify the district regulations of this Ordinance and provide for specific areas of exception.

1   Encroachments on Required Yards. Every part of a required yard shall be open and unobstructed from finished grade upward, except as specified herein.

   A.    Architectural projections, including roofs which cover porches, enclosed porches, window sills, belt courses, cornices, eaves, flues and chimneys, and ornamental features may project three feet (3') into a required yard.

   B.    Terraces, patios, uncovered decks, and ornamental features which have no structural element more than two feet (2') above or below the adjacent ground level may project ten feet (10') into a required yard. However, all such projections must be set back at least three feet (3') from an adjacent side lot line; or and twenty feet (20') from any street property line.

   C.    ADA ramps servicing a dwelling unit may be projected 11 feet (11') into a required yard.

   D.    Fire escapes, fireproof outside stairways, and balconies opening to fire towers may project a maximum of 3 feet (3') into required yards, provided that they do not obstruct the light and ventilation of adjacent buildings.

   E.    For buildings constructed upon a front property line, a cornice may project into public right- of-way. Maximum projection is the smaller of four feet (4') or five percent (5%) of the right- of-way width.

   F.    Canopies. In commercial districts, a canopy may extend into a required front yard, provided that the canopy is set back at least five feet (5') from the front property line, covers less than fifteen percent (15%) of the area of the required front yard, and has a vertical clearance of at least eight feet six inches (8'6").

2.    Garage Setbacks: Any garage, detached or attached, that fronts on a public street must be set back at least 20 feet (20') from such street or as is required by the minimum setback requirements of the zoning district, whichever is greater.

3.    Built-Up Blockfaces: These provisions apply if forty percent (40%) or more of the buildings on that blockface have front yard setbacks different from those required for the specific district.

   A.    If a building is to be built on a parcel of land within 100 feet (100') of existing buildings on both sides, the minimum front yard shall be the mean setbacks of the adjacent buildings.

   B.    If a building is to be built on a parcel of land within 100 feet (100') of an existing building on one side only, the minimum front yard shall be the setback of the adjacent building.

   C.   If a building is to be built on a parcel of land not within 100 feet (100') of an existing building on either side, then the minimum front yard shall be the mean setback of all existing buildings on the blockface.

   D.   No setback adjustment pursuant to this section shall create a required front yard setback more than five feet (5') greater than that otherwise required by the applicable zoning district.

4.    Lots Adjoining Alleys. In calculating the depth of a required side or rear yard setback for a lot adjoining a dedicated public alley, one-half of the alley may be credited as a portion of the yard. However, no structure may be nearer than three feet (3') to the near side of the alley.

5.    Corner Lots. Required setbacks shall not reduce the buildable width of any corner lot to less than 24 feet (24'). Appropriate setback adjustments shall be allowed to maintain this minimum width.

6.    Rear Yard Exceptions - Residential Uses. When an irregular lot is used for residential purposes, the rear yard may be measured as the average horizontal distance between the building and rear lot line, provided that the minimum setback shall not be less than sixty percent (60%) of the rear yard required by the zoning district.

7.    Double Frontage Lots. Double-frontage lots shall require full front-yard setbacks along both street frontages, as set forth in the bulk regulations table of each zoning district. Residentially zoned double-frontage lots on a major street, and with no access to that street may have a 25-foot (25') minimum front yard setback along said street.

8.   Satellite Antennas. Antennas with a surface area over 6.3 square feet which are accessory to a primary use and are designed to receive and transmit electromagnetic signals, or to receive signals from satellites, shall not be located within any front yard of the primary use. Such antennas shall be located no less than fifteen feet (15') from the property line of an adjacent property within a residential zoning district.

9.   Lamp Posts: Lamp posts with a maximum height of ten (10) feet, and flag poles up to maximum height of base district may be located within required yards, provided they are set back at least five (5) feet (5') from property lines.

10.   Vision Clearance Zones. No structure, including a fence, shall be built to a height of more than three feet (3') above the established curb grade on the part of the lot bounded by the street lines of the streets which intersect and a line connecting a point on each of such lines thirty feet (30') from their point of intersection. No landscaping shall be planted in such area which will materially obstruct the view of drivers approaching the street intersection.

These provisions allow exceptions to the height limit of any zoning district in certain situations.

1.   Vertical Projections. Chimneys, cooling towers, building mechanical equipment, elevator bulkheads, fire towers, grain elevators, non-parabolic receiving antennas, tanks, solariums, steeples, penthouses not exceeding 25 percent of total roof area, flag poles, stage towers or scenery lofts, and water towers may be built to any height in accordance with existing and future ordinances.

2.   Amateur Radio Towers and Federal Communication Commission Pronouncements. Radio towers, antennas and other appurtenances operated by licensed amateur radio operators, where permitted and when, may not exceed 75 feet in height. This height has been determined by the City to reasonably accommodate amateur service communications, and further represents the minimum practicable regulation to accomplish legitimate municipal land use regulation purpose, as recognized under published guidelines of the Federal Communications Commission.

   A.   Special instances may require that amateur radio tower heights exceed 75 feet to achieve effective and reliable communications. In such cases, the Board of Adjustment may grant a Conditional Use Permit to a licensed amateur radio operator for a specific tower height that exceeds 75 feet. In determining whether to grant such permission, the City Council shall consider the federal guidelines contained in PRB-1 (Amateur Radio Preemption, 101 FCC 2d (1985); codified at C.F.R. Section 97.15(e).

   B.   Such radio towers shall not be located within any front yard of the primary use.

3.   Broadcast Towers. Broadcast towers, when operated by a federally-licensed commercial or non-profit organization, may be built to any height in accordance with existing and future ordinances. This exception does not apply to radio towers, antennas and other appurtenances operated by licensed amateur radio operators.

4.   Civic Buildings. Buildings housing civic use types may be built to a maximum height of 60 feet. Such buildings located in residential districts shall be set back one foot in addition to required setbacks from each property line for each foot of height over the maximum height of the zoning district.

5.   Wind Energy Conservation Systems (WECS).

   A.   The distance from all lot lines or any building or power line to any tower support base of a WECS shall be equal to the sum of the tower height and the diameter of the rotor. A reduction of this requirement may be granted as part of a Conditional Use Permit approval if the Planning Commission finds that the reduction is consistent with public health, safety, and welfare.

   B.   The distance between the tower support bases of any two WECS shall be the minimum of five rotor lengths, determined by the size of the largest rotor. A reduction of this requirement may be granted as part of a Conditional Use Permit approval if the Planning Commission finds that the reduction does not impede the operation of either WECS.

   C.   The WECS operation shall not interfere with radio, television, computer, or other electronic operations on adjacent properties.

   D.   A fence six feet high with a locking gate shall be placed around any WECS tower base; or the tower climbing apparatus shall begin no lower than twelve feet above ground.

   E.   The WECS is exempt from the height restrictions of the base district.

6.   Conditional Use Approvals. The Board of Adjustment may grant an exception from the height limit for a zoning district for a Conditional Use as part of its approval of that use. The limit or extent of this exception shall be a specific part of the special use permit.

7.   Federal Aviation Administration Rules. No structure may be built in any zoning district which exceeds the maximum height permitted under the rules of the Federal Aviation Administration. These rules describe the glide angles and operational patterns for any airport within the planning jurisdiction of the City of Mount Vernon.

In the instance that the ordinance provides, the city may authorize such subdivisions to allow for greater flexibility in the design and development of subdivisions, in order to produce innovative residential environments, to provide for more efficient use of land, to protect topography and to encourage the preservation of common area and open space. These special regulations and design exceptions apply only to creative subdivisions.

1.   Site Area Per Unit. Unless otherwise provided, the site area per unit for a creative subdivision as a whole shall be that of the zoning district in which such subdivision is located. For the purpose of computing site area per unit, the area of public streets and private ways within the subdivision must be excluded. Residential use types may be combined within the creative subdivision provided that the subdivision as a whole complies with the required maximum density of the zoning district.

2.   Perimeter Yards.

   A.   Structures must maintain normal street yard setbacks from any public streets that form the perimeter of the development.

   B.   Structures must maintain a 20 foot minimum side-yard setback from any property line that forms the boundary of the development.

3.   Area and Yards for Individual Lots.

   A.   Individual lots within a creative subdivision are exempt from minimum lot area or yard setback requirements set forth elsewhere in this Ordinance, unless provided for by the regulations for a specific zoning district. A creative subdivision must be planned and developed as a common development. A minimum separation of twenty (20) feet shall be established for all residential structures not attached to one another, unless the City Council grants a specific exception for developments proposing unique circumstances, only in as much as said development can be demonstrated to avoid detriment to Mount Vernon's efforts to protect public health, safety, welfare, community character, property values and aesthetics.

   B.   Any private garage oriented to or facing a public street or private way internal to the creative subdivision must be set back a minimum of 25 feet from that public street or private way.

4.   Coverage and Landscaping Requirements. Individual lots in a creative subdivision are exempt from maximum building and impervious coverage limitations and street yard landscaping requirements established for the zoning district. However, the subdivision as a whole, including streets, walks, and access ways, must comply with the building and impervious coverage regulations for its zoning district.

1.   Location Restriction. Unless otherwise provided by this Ordinance or other sections of the Mount Vernon Municipal Code, no fence shall be built on any lot or tract outside the surveyed lot lines, or adjacent to any Municipal property, excluding public streets.

2.   Required Openings. Unless otherwise provided by this Ordinance or other sections of the Mount Vernon Municipal Code, any fence built on residential property within required front or street side yards shall contain openings constituting no less than 50 percent of the surface area of the fence.

3.   Sight Obstruction. No solid fence permitted or required by this article or other sections of the Mount Vernon Municipal Code shall be built within a triangle formed by the adjacent side lines of two intersecting streets and a line connecting points 30 feet on each leg from their point of intersection; or otherwise in any manner create a traffic hazard or obstruction to visibility.

4.   Facing. The finished surfaces of any fence shall face toward adjacent properties and street frontage.

5.   Effect on Adjacent Properties. No accessory building shall damage adjacent property by obstructing views, inhibiting solar access, or hindering ventilation.

6.   Swimming Pools and Hot Tubs. Any parcel in the City of Mount Vernon containing a permanent outdoor swimming pool or hot tub, whether above ground or below, with a depth greater than 18”, or capacity greater 5,000 gallons, shall provide for a fence that shall meets regulations contained in the Mount Vernon Zoning Ordinance.

7.   Residential Fences. Fences constructed within residential districts or on land used for residential purposes are subject to the following provisions.

   A.   Height: The maximum height of a fence within a required front yard or street side yard shall be four feet. The maximum height for any other fence shall be six feet.

   B.   Exception for Street Side Yards: On corner lots, a fence built parallel to the street side yard line but set back in conformance with the required street yard setback may have a maximum height of six feet.

   C.   Exception to Openness Requirement: Fences built on residential property other than a required front or street side yards may exceed 50 percent closed construction.

   D.   Exception for Front Yards of Double Frontage Lots: A fence built within the required front yard of a double frontage lot may be a maximum of six feet in height and may exceed 50 percent closed construction if such lot fronts an arterial street or expressway, as defined in the Comprehensive Plan or the street planning map of the City of Mount Vernon; and if such frontage does not provide primary access to the property.

   E.   Materials: Fences shall be constructed of wood, chain-link, PVC/ resin, metal, stone or masonry materials only. Wood fences shall utilize standard building lumber only. Barbed wire and/or electrified fences are not permitted, and are defined as any fence that includes in its material barbs, blades, razors, electric current or other features specifically designed to injure or abrade an individual or animal who attempts to negotiate the fence.

8.   Civic, Office, Commercial, and Industrial Fences. Fences constructed in commercial and industrial districts are subject to the following special provisions:

   A.   The maximum height of a fence for any permitted use in any non-residential zoning district shall be eight feet.

   B.   Civic Uses in Residential Districts: The maximum height of fences installed as part of Primary and Secondary Educational Facilities or Park and Recreation Use Types within Residential Zoning Districts shall be eight feet.

   C.   The Board of Adjustment may approve greater fence heights on a case-by-case basis if it concludes that such permission furthers the health, safety, and welfare of the residents of the City of Mount Vernon.

   D.   Barbed wire shall not be used in the construction of any fence outside of the LI Limited Industrial Zoning District. Barbed wire may be used in the construction of fencing in an industrial district provided that the bottom strand of the wire shall be at least six feet above ground level.

   E.   Electrified fences are not permitted within the jurisdiction of the City of Mount Vernon.

9.   Fences on Easements. Fences may be constructed within both public and private utility and drainage easements provided:

   A.   The fence and its design is subject to the approval of the City Engineer.

   B.   Removal and/or subsequent replacement of the fence or a portion thereof for the purpose of utilizing the easement shall be at the property owners expense.

Denial, revocations, or cancellations of a building permit based on the provisions of this Section may be appealed to the Board of Adjustment, as set forth in Article 13.

Accessory uses and buildings are subject to all site development regulations of its zoning district, except as provided below:

1.   Setbacks:

   A.   Side Yards: An accessory building may be located a minimum of five feet (5') from the side lot line of the property if it is located between the rear building line of the principal building and the rear property line.

   B.   Front Yards: No accessory building may be located between the front building line of the principal building and the front property line.

   C.   Rear Yard: The minimum rear yard setback for accessory buildings shall be 8 feet (8'). This minimum rear yard setback shall be increased to 15 feet (15') if the accessory building requires vehicular access from an alley.

   D.   Street Yards: No accessory building shall be located within 20 feet from any street side yard property line.

   E.   Easements: Easements may be incorporated into these required setbacks. however, no accessory building shall be located within any easement or right-of-way along the property line.

2.   Maximum Size:

   A.   No accessory building shall exceed 144 square feet, or 1.5% of total lot area, whichever is larger, within an SR, TR, or HR residential district., with the exception of an accessory dwelling unit or detached garage.

   B.   All buildings on a site, taken together, must comply with the building coverage requirements for the zoning district.

   C.   The maximum square feet of any detached garage or accessory dwelling unit shall not exceed 100% of the primary dwelling unit's ground floor square feet, alone or in combination, excluding any attached garage square feet. Dwelling space which may occupy a half story is not subject to this limit, however, the area limit applied for an accessory dwelling unit between this section and section 610 shall be the most restrictive limit.

3.   Height:

   A.   In residential districts, the maximum height shall be 12 feet (12') for a detached garage and 10 feet (10') for any other accessory building.

   B.   Additionally and without any increase to the height of the sidewalls of a detached garage or accessory building based on the aforementioned maximum height limitations, the height and pitch of the roof may be increased if, in the discretion of the Zoning Administrator, that increase is necessary to complement the pitch and style of the primary residential structure.

   C.   In no event shall a detached garage or accessory building exceed the height of 20 feet (20'), as measured from the established grade to the highest point of the structure.

4.   Separation from Other Buildings: No accessory building shall be placed within ten feet of any other building on its own property or any adjacent properties.

5.   Attached Accessory Buildings: Any accessory building physically attached to the principal building shall be considered part of the principal building and subject to the development regulations of its zoning district.

6.   Effect on Adjacent Properties: If an adjacent lot is built upon, the accessory building must be entirely to the rear of the line of any principal building on such adjacent lot. No accessory building shall damage adjacent property by obstructing views, inhibiting solar access, or hindering ventilation.

7.   Hazards: Any accessory use which creates a potential fire hazard shall be located a minimum of 10 feet from any residential structure. Such uses include but are not limited to detached fireplaces, barbecue ovens, or storage of flammable materials.

8.   No accessory building shall be built upon any lot until construction of the principal building has begun.