Title
Discussion on Residential Density Calculations
The purpose of this discussion item is to evaluate whether the Village’s current approach to residential density calculations - based on Net Buildable Acres - continues to effectively support community goals, and to consider targeted amendments that better align with contemporary development practices and fiscal sustainability.
History
In October 2025, a text amendment was presented to the Board of Trustees (Case #2025-0584) that proposed modifying how dwelling units per acre are calculated in residential zoning districts. The amendment recommended shifting from a net buildable acreage standard to a gross acreage approach. The Board did not approve this change, signaling a preference to retain a framework that accounts for site-specific constraints in determining allowable density.
Staff is proposing an alternate amendment for your consideration.
In the R-3, R-3A, R-4, and RSB zoning districts, residential density is currently calculated based on net buildable acreage. The proposed amendment refines the definition of net buildable acreage and updates the density bonus criteria to improve clarity, consistency, and alignment with the Village’s broader growth and development objectives. This approach provides numerous benefits to both the Village and the development community.
How is Density Calculated
In the R-3, R-3A, R-4 and RSB Zoning Districts, density of a development is calculated based on the Net Buildable Acreage.
Current Definition
Net Buildable Acres are calculated by deducting the following from the gross acreage of land:
• 50% of ComEd easement if owned by the petitioner and the space serves as a public open space amenity
• Floodplain that must be conserved
• Wetlands that must be conserved by federal, state, or local requirements
• Perimeter road right-of-way (ROW) dedication
• 50% of land required for a park or school dedication
• Detention and retention areas up to the high-water level
Of the above 6 deductions:
The first three reflect fixed, pre-existing site constraints
The ROW dedication contributes to public and may not need to be deducted from gross acreage
The last two deductions are policy-driven requirements that are not known in the preliminary project stages
Proposed Definition
Net Buildable Acres are calculated by deducting the following from the gross acreage of land:
• 50% of ComEd easement if owned by the petitioner and the space serves as a public open space amenity
• Floodplain that must be conserved
• Wetlands that must be conserved by federal, state, or local requirements
BENEFITS OF PROPOSED MODIFICATIONS
BENEFITS TO THE VILLAGE
• Lowers infrastructure cost per unit -
o fewer linear feet of road per household
o shorter utility runs
o more efficient stormwater systems
• Reduces long term maintenance liabilities
• Yields higher property tax/acre
• More efficient service delivery
• Better use of existing infrastructure
• Plan review efficiency for Village Staff & Consultants
• Benefits extend across multiple jurisdictions, including schools, fire, police etc.
BENEFITS TO DEVELOPERS
• Improves predictability by focusing on “buyer beware” conditions (wetlands, easements, floodplain)
• Reduces upfront engineering costs, entitlement risk and plan review time
• Eliminates circular deductions tied to final unit count
• Provides flexibility to accommodate evolving requirements (e.g., stormwater regulations)
WHY NOT A FULL SHIFT TO GROSS DENSITY?
While a gross density model offers simplicity, it represents a more significant policy shift and removes the ability to account for site-specific constraints (like wetland and floodplains) within the density calculation itself. A modified definition of net buildable acreage achieves many of the same benefits - clarity, predictability, and efficiency - while preserving a more tailored and context-aware framework.
Density Bonuses
In addition to base density calculations, the Land Development Code (LDC) includes a framework that allows developers to avail of density bonuses as follows:
Current Bonus Structure (Dwelling Units per Acre)
Zoning District Net DU/Ac Max DU/Ac w/ Bonuses
R-3, R-3A 2.5 4 (60% increase)
R-4 3.5 6 (71% increase)
RSB 4 8 (100% increase)
While these bonuses are achievable in large, master-planned developments, they present huge challenges for smaller or infill projects due to:
• Limited site area
• Physical constraints
Additionally, some bonus criteria - such as boulevard medians - are now discouraged due to impacts on emergency access, maintenance, and snow removal. As a result, the current bonus structure needs to be evaluated and revised.
CURRENT FRAMEWORK FOR DENSITY BONUSES
1 unit per acre for every additional 20% of common open space over the minimum required
And
1 unit per acre for every 1200’ of boulevard treatment design
And
1 unit per acre if all other optional bonuses are provided
Optional Density Bonuses
• Orientation of more than 50% of buildings that provide views of common open space, forests, valleys, ponds, wetlands and hills
• Less than 50% of garage doors facing the street or common courtyard
• Garbage enclosures and places for recreational vehicles hidden from view from the street
• Buildings oriented for solar heating
• Boulevard treatment of a street, including a wide landscaped median strip or island in the middle of a street
• Attractive non-standard, but consistent, style for lampposts and signs, varied pavement treatments, tiles, stones, bricks and mosaics
PROPOSED FRAMEWORK FOR DENSITY BONUSES
1 unit per acre for every additional 20% of common open space over the minimum required
And
1 unit per acre for every 1200’ of enhanced streetscape (hardscape and landscape) design
And
1 unit per acre if all other optional bonuses are provided
Optional Density Bonuses
• Orientation of more than 50% of buildings that provide views of common open space, forests, valleys, ponds, wetlands and hills
• Less than 50% of garage doors facing the street or common courtyard
• Garbage enclosures and places for recreational vehicles hidden from view from the street
• Potential additional incentives listed below
What do we want to incentivize in residential planned developments?
• Enhanced Common open space with public art, multi use paths, natural features, playground equipment
• Green infrastructure including bioswales, rain gardens, green roofs exceeding Village’s requirements
• Preservation of mature trees or natural features
• Exceeding baseline Design Standards
• Mixed use development, including ground level commercial/retail
• Housing diversity - age-friendly design
• Inclusion of renewable energy (solar, geothermal)
• Redevelopment and infill sites, including brownfield parcels
• Traffic calming measures
• Larger caliper trees, and plant materials size that exceeds Village’s requirements
• Dry bottom detention ponds that serve as park areas
Recommended Action/Motion
Discussion only.