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GENERAL PROVISIONS FOR CONSERVATION DESIGN OPTION
(A) A conservation design subdivision designed in accordance with this section and § 154.251 is a by-right permitted use option in the E-1, E-2, R-1, R-2, R-2A, R-3 and R-4 zoning districts. Other development options include a conventional residential subdivision or a planned unit development residential subdivision. When this option is utilized, the regulations of this section are intended to encourage subdivision designs that are more efficient and provide more open space and greater natural resource protection than conventional subdivision designs. One goal of conservation design subdivisions is to allow more compact and less costly networks of streets and utilities. They may also help preserve aquifer recharge, reduce stormwater runoff, reduce non-point source pollutant loading rates and preserve an area’s semi-rural character. Conservation design subdivisions are intended to encourage the provision of open space and recreational amenities for residents and preserve natural, environmentally sensitive and other resources.
(B) The conservation design subdivision standards of this section require that a specified portion of each development be set aside and permanently preserved as open space, which can be used to provide recreational opportunities for the subdivision’s residents and/or to conserve and protect significant natural resources, in accordance with the regulations of this chapter.
(C) Review period. No later than five years from the date of passage of the initial Conservation Design Ordinance, the County Board, or a committee, subcommittee or commission thereof, shall consider whether amendments are necessary to make this section, §§ 154.251, 154.265 through 154.269 and 154.280 through 154.286 consistent with recommendations of the Land Resource Management Plan, to encourage new or improved conservation design building practices which may have been developed and which may have application in the county, to correct deficiencies or difficulties which may have developed in administration of §§ 154.250, 154.251, 154.265 through 154.269 and 154.280 through 154.286, or for other reasons as the County Board may determine.
(Ord. passed 7-8-1970; Res. 09-167, passed 6-18-2009) Penalty, see § 154.999
(A) Conservation design subdivisions are subject to all other subdivision design and improvement standards of this chapter unless otherwise expressly stated.
(B) Lots and development sites within conservation design subdivisions must, to the maximum extent practical, be located outside of areas containing woodlands, grasslands, surface waters, steep slopes, drainageways, rock outcroppings and other natural resource features. See the figure below. A natural resources inventory report, that includes site specific data, prepared by the Will/South Cook Soil and Water Conservation District shall be submitted to aid in identifying areas that merit conservation.
(C) Impervious areas must be limited and, to the maximum extent practical, be sited and designed to minimize stormwater runoff impact to the watershed’s receiving waters by:
(1) Minimizing concentrated stormwater flow;
(2) Minimizing and breaking up or disconnecting large areas of impervious surface into smaller areas;
(3) Maximizing the use of sheet flow through vegetated areas;
(4) Maximizing the flow length through vegetated areas;
(5) Encouraging groundwater recharge; and
(6) Providing natural preserve areas where natural soils will remain undisturbed and soil compaction activities are prohibited.
(D) Stormwater best management practices (BMPs) shall be used to protect water quality, preserve natural hydrology and minimize overall impacts of development on aquatic resources. BMPs may include, but not be limited to, the following practices:
(1) Use of naturalized detention basins designed to maximize removal and transformation of run-on pollutants;
(2) Use of wet-bottom detention basins and native, emergent vegetation along their periphery and in bottoms of wetland basins;
(3) Use of stilling basins at major detention basin inlets and use of maximum distances between major inlets and outlets;
(4) Where detention basins discharge into adjacent or downstream wetlands, use of detention basins outlet structures designed to spread and infiltrate run-off through use of level spreader devices;
(5) Use of bio-swales in lieu of stormwater piping;
(6) Use of permeable pavers where practical; and
(7) Curb and gutter, pavement widths, right-of-way widths and sidewalk requirements will be waived or modified in a conservation design subdivision contingent upon the approval of the appropriate highway authority.
(Ord. passed 7-8-1970; Res. 09-167, passed 6-18-2009) Penalty, see § 154.999
DETERMINING MAXIMUM DEVELOPMENT POTENTIAL
(B) Regardless of the method chosen (yield formula or yield plan), the following zoning district base densities apply:
Zoning District | Maximum Base Density (units per acre [UPA]) |
Zoning District | Maximum Base Density (units per acre [UPA]) |
E-1 | 0.200 |
E-2 | 0.400 |
R-1 | 0.726 |
R-2 | 1.000 |
R-2A | 1.452 |
R-3 | 2.178 |
R-4 | 3.485 |
(C) If the conservation design subdivision is located in more than one zoning district, the maximum number of dwelling units allowed must be determined separately for each portion of the site lying within a different zoning district. Density may be transferred from one portion of the site to another, provided that the transfers do not result in an increase in the number of dwelling units allowed on the overall site.
(Ord. passed 7-8-1970; Res. 09-167, passed 6-18-2009)
(A) Developers may elect to submit a yield plan to be used as the basis for determining the maximum number of dwelling units allowed prior to bonus calculations.
(B) Yield plans (subdivision plans) must be prepared by an engineer, surveyor, professional planner or other qualified professional.
(C) The yield plan must be prepared in sufficient detail and include sufficient backup documentation to illustrate the maximum number of dwelling units that would realistically be allowed on the property under conventional subdivision design, in compliance with this chapter, the Zoning Ordinance, Water Resource Ordinances, Stormwater Management Ordinance and all other applicable ordinances.
(D) Yield plans must be reviewed and approved by the Chief Subdivision Engineer as part of the plat approval process for the conservation design subdivision.
(Ord. passed 7-8-1970; Res. 09-167, passed 6-18-2009)
(A) Generally. In lieu of the yield plan method of § 154.266, developers may elect to use a yield formula to be used as the basis for determining the maximum number of dwelling units allowed prior to bonus calculations.
(B) Step 1 - Determine base site area. The first step of the yield formula involves calculating the site’s base site area, as follows:
1. Determine gross site area | acres |
2. Subtract ROW of existing streets (and ultimate ROW) | - acres |
3. Equals base site area | = acres |
(C) Step 2 - Determine net site area. The second step of the yield formula involves calculating the net site area, as follows:
1. Take base site area (from division (B) above) | acres |
2. Subtract regulated wetlands (> than 0.1 acres in area) and wetland buffers as required by the County Water Resource Ordinances or United States Army Corps of Engineers, whichever is more stringent: | - acres |
3. Equals buildable area | = acres |
4. Subtract 10% of buildable area for stormwater management | - acres |
5. Subtract 15% of buildable area for streets | - acres |
6. Equals net site area | = acres |
(D) Step 3 - determine number of dwelling units allowed. The third step of the yield formula involves a final calculation of the maximum number of dwelling units allowed on the site:
1. Take net site area (from division (C) above) | acres |
x UPA | |
3. Equals pre-bonus maximum number of dwelling units allowed | = units |
(Ord. passed 7-8-1970; Res. 09-167, passed 6-18-2009)
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