Zoning and Codes Skill

Selection Decision Tree

1. Is the project a comprehensive code replacement for an entire jurisdiction? --> Consider Transect-Based (SmartCode)
2. Is the project focused on a specific plan area (downtown, corridor, TOD)? --> Use Form-Based Code for the plan area
3. Does the area have complex environmental constraints (floodplain, noise, contamination)? --> Layer Performance standards as an overlay
4. Are existing suburban residential areas stable and not targeted for change? --> Retain Euclidean zoning for those areas
5. For most real-world jurisdictions --> Use a Hybrid approach combining the above as appropriate

2. Transect Zone Specifications

The Transect is a cross-section of the human habitat ranging from the most natural (T1 Natural Zone) to the most urban (T6 Urban Core Zone). Each zone has a distinct character defined by calibrated standards for density, building form, frontage, street type, and permitted uses. The following table provides complete specifications for all six zones plus Special Districts (SD).

Complete T1-T6 Parameter Table

Transect Zone Character Descriptions

T1 Natural Zone: Lands approximating or reverting to a wilderness condition, including lands unsuitable for settlement due to topography, hydrology, or vegetation. These are permanently protected areas that provide ecosystem services (water filtration, carbon sequestration, biodiversity habitat, flood control) and recreational value. No buildings except minor structures for conservation management and passive recreation (trails, observation platforms, restrooms).

T2 Rural Zone: Sparsely settled lands in open or cultivated state. These include woodland, agricultural land, grassland, and scattered buildings. The landscape is the dominant element; buildings are subsidiary. Typical settlement includes farmsteads, rural estates, and very small hamlets. Roads are typically two-lane without curbs, with open swales for drainage. The boundary between T2 and T3 is one of the most important in the transect, as it defines the edge of the neighborhood.

T3 Sub-Urban Zone: Low-density residential areas with predominantly detached buildings set back from tree-lined streets. Yards and landscaping are significant elements of the streetscape. Blocks are larger (150-250m) and streets are curvilinear or grid. This is the typical post-war suburban condition, but the transect version emphasizes connectivity, sidewalks, street trees, and proximity to neighborhood centers.

T4 General Urban Zone: The workhorse zone of a walkable neighborhood. Medium-density, mixed-use (by right), with a defined streetwall of moderate height (2-5 stories). Buildings have shallow front setbacks (2-5m) and form a continuous or near-continuous street edge. Ground floors may be residential or commercial depending on location. Streets are well-connected in a grid or modified grid, with on-street parking, street trees, and sidewalks on both sides.

T5 Urban Center Zone: The main street, town center, or downtown of a neighborhood, district, or small city. Higher density, wider variety of uses, more active ground floors, and taller buildings than T4. The streetwall is consistent and buildings are built to or near the front lot line. Ground floors are predominantly commercial (retail, restaurant, service). Upper floors are residential, office, or hotel. Parking is structured or underground, never surface lots facing the street.

T6 Urban Core Zone: The highest-intensity zone, found in city centers and major regional downtowns. Towers and high-rise buildings of significant height. Maximum variety and intensity of uses. Civic buildings and institutions of regional significance. Major transit infrastructure (rail stations, bus terminals). Public spaces are formal and hardscaped (plazas, civic squares, promenades). This zone typically applies only in the largest cities and in very limited geography.

3. Form-Based Code Elements

A form-based code consists of several integrated components that work together to regulate the physical form of development. Each component addresses a distinct aspect of the built environment.

3.1 Regulating Plan

The regulating plan is the coded map that designates transect zones, civic space locations, special district boundaries, and thoroughfare types for every parcel within the plan area. It is the spatial expression of the code and the primary reference document for any applicant.

• Maps transect zones (T1-T6) to specific parcels or blocks
• Identifies mandatory building frontage lines (build-to lines)
• Designates required ground-floor retail frontages
• Locates civic space reservations (plaza, green, park)
• Shows thoroughfare types for every street segment
• Identifies special districts with unique standards (civic, waterfront, transit, historic)
• May include sub-area plans for complex sites

3.2 Building Form Standards

Building form standards regulate the physical envelope and configuration of buildings. These are the core of the form-based code and replace the bulk and dimensional standards of conventional zoning.

• Height: maximum stories and meters, measured from grade to highest occupied floor (or roof peak, depending on code), with exceptions for mechanical equipment, elevator overruns, parapets (typically +1.5m), and architectural features (spires, cupolas)
• Setback / Build-to Line: front setback is typically expressed as a build-to line (BTL) with a required percentage of building facade that must be located at the BTL (typically 70-90% in urban zones)
• Coverage: maximum building footprint as percentage of lot area
• FAR: maximum ratio of total floor area to lot area, with rules for calculation (e.g., structured parking excluded, mechanical rooms excluded, balconies excluded if open)
• Building Type: the permitted physical configurations (detached house, rowhouse, apartment building, mixed-use building, tower, etc.), each with its own sub-standards
• Disposition: the placement of the building on the lot (edgeyard, sideyard, rearyard, courtyard) -- determines how the building relates to the street and to open space

3.3 Frontage Type Standards

The frontage is the interface between the building and the public realm. Frontage type standards regulate the configuration of the ground floor and the zone between the facade and the lot line.

3.4 Public Space Standards

Public space standards regulate the design and programming of the civic realm, including parks, plazas, greens, squares, playgrounds, and community gardens.

3.5 Thoroughfare Standards

Thoroughfare standards define the cross-section, character, and design parameters for every street type in the code. These replace conventional transportation engineering standards with context-sensitive designs.

• Each thoroughfare type gets a full cross-section specification (see the Street Design skill for detailed cross-section methodology)
• Thoroughfare types are assigned to the regulating plan by segment
• Standards cover: ROW width, travel lanes (number and width), parking (type and width), bike facilities, sidewalk zones, median, planting, lighting
• Typical thoroughfare types: boulevard, avenue, commercial street, neighborhood street, residential street, rear lane/alley, passage, shared street, path/trail

3.6 Signage Standards

Signage standards regulate the type, size, placement, and illumination of signs to ensure visual quality and consistency.

• Projecting signs: perpendicular to facade, max 0.6 sqm per sign, min 2.4m clearance above sidewalk, max projection 1.2m
• Wall signs: flat on facade, max 10% of facade area or 2.0 sqm (whichever is less in T3-T4, greater in T5-T6), letter height max 300mm (T4), 450mm (T5), 600mm (T6)
• Awning/canopy signs: text on valance only, max letter height 200mm
• Window signs: max 25% of window area, no flashing or animated
• Monument signs: ground-mounted, max 1.2m height (T3), 1.5m (T4), not permitted T5-T6
• Illumination: external illumination (gooseneck, wash) permitted all zones; internal illumination (backlit channel letters) permitted T5-T6 only; neon permitted T5-T6 only; no flashing, scrolling, or animated signs

3.7 Architectural Standards (Optional Companion)

Architectural standards are typically advisory (guidelines) rather than mandatory (code), but some form-based codes include mandatory provisions for key elements.

• Materials: primary facade materials (masonry, stucco, wood clapboard, metal panel); prohibited materials (EIFS below 2.4m, vinyl siding in T5-T6, exposed concrete block); material transitions at inside corners only (not outside)
• Fenestration: minimum ground-floor transparency (60-80% in T5-T6 shopfronts, 30-50% in T4), upper-floor window-to-wall ratio (20-40%), window proportions (vertical orientation preferred), prohibited: mirrored glass, all-glass curtain wall below T6
• Rooflines: flat roofs with cornice or parapet (T5-T6), pitched roofs 6:12 to 12:12 (T3-T4), roof material standards, mechanical screening required
• Color: typically advisory, may regulate in historic districts
• Parking structure facades: must be wrapped with habitable space on all street-facing facades, or designed with architectural facade treatment that conceals the parking structure

4. Building Envelope Controls

Building envelope controls define the three-dimensional volume within which a building may be constructed. These are the most precise regulatory tools in a zoning code.

4.1 Height Controls

4.2 Setback and Build-to-Line Controls

Build-to-line (BTL) is fundamentally different from a setback. A setback defines a minimum distance from which a building must be placed; a BTL defines a line at which the building facade must be placed. The BTL creates a consistent streetwall. The "compliance percentage" specifies how much of the lot width must have building facade at the BTL (the remainder may be recessed for courtyards, forecourts, or entries).

4.3 Lot Coverage

Maximum percentage of the lot area that may be covered by the building footprint:

• T3: 30-50% (significant open space on lot)
• T4: 50-70% (moderate open space)
• T5: 70-90% (minimal open space, may be on upper levels)
• T6: 80-100% (nearly full lot coverage, open space on rooftops or at upper setbacks)

Coverage calculations typically include: all roofed structures, covered porches and galleries (if enclosed on three sides), but exclude: uncovered terraces, pergolas (if less than 50% covered), at-grade patios, underground structures.

4.4 Floor Area Ratio (FAR)

FAR = Total Floor Area / Lot Area. This controls the overall bulk and density of development.

FAR calculation inclusions: all enclosed floor area measured to outside face of exterior walls, mezzanines, occupied basements, enclosed balconies. FAR calculation exclusions: structured parking (often excluded to encourage structured over surface parking), mechanical rooms, unenclosed balconies, residential storage rooms below 5 sqm, ground-floor retail in mixed-use buildings (incentive exclusion in some codes). FAR bonuses: additional FAR may be earned through provision of affordable housing (+0.5-2.0 FAR), public open space (+0.5-1.0 FAR), transit infrastructure contributions (+0.5 FAR), LEED/green certification (+0.5 FAR), heritage preservation (+0.5-1.0 FAR). Bonuses are typically capped and cannot exceed the maximum FAR.

4.5 Sky Exposure Plane

The sky exposure plane is an angular plane that limits building height above a certain base height at the street setback line. It ensures daylight and sky access at the street level.

• Base height: the height at the setback line at which the angular plane begins (typically the streetwall height: 12-24m depending on zone)
• Angle: the angle of the plane measured from the horizontal at the setback line (typically 70-80 degrees from horizontal, or equivalently a slope of approximately 2.5:1 to 5.7:1)
• Application: the building may not penetrate the sky exposure plane on any street-facing facade
• Calculation: at any point along the facade, maximum height = base height + (distance from setback line x tangent of angle)
• Exemptions: mechanical bulkheads, elevator overruns, and architectural features (if within permitted exceptions)

Example: Base height 18m, angle 75 degrees from horizontal. At 5m setback from facade line: max height = 18 + (5 x tan75) = 18 + 18.7 = 36.7m.

4.6 Step-Back Requirements

Step-backs require upper portions of a building to be set back from the lower streetwall facade, reducing the visual bulk of taller buildings and preserving the pedestrian-scale streetwall experience.

• Streetwall height: the height at which the step-back occurs (typically 4-6 stories, or 15-22m)
• Step-back depth: the minimum horizontal distance the upper floors must be set back from the streetwall facade (typically 3.0-6.0m)
• Application: required on all street-facing facades (may not be required on alley-facing or interior facades)
• Rationale: preserves the 1:1 to 1:2 street-width-to-building-height ratio at the pedestrian level, which research identifies as the most comfortable enclosure ratio for urban streets

4.7 Tower Separation

For buildings with tower elements (above the podium/streetwall), minimum separation distances prevent a canyon effect and ensure light, air, and privacy.

• Tower-to-tower (same site): minimum 24m face-to-face
• Tower-to-tower (adjacent sites): minimum 24-30m center-to-center
• Tower floor plate: maximum 750-2,000 sqm (varies by zone; smaller plates improve light penetration and reduce wind effects)
• Tower lot coverage: maximum 40-50% of lot area (the tower footprint, not the podium footprint)
• Point tower preferred: slender towers with floor plates under 1,000 sqm minimize shadow, wind, and view impacts

4.8 Lot Dimensions

Maximum lot and block dimensions prevent superblocks and ensure a fine-grained, walkable urban fabric with frequent cross-streets, mid-block passages, and varied building frontages.

5. Code Generation Workflow

This section provides a step-by-step process for producing a form-based code from a masterplan or area plan. Follow these steps sequentially.

Step 1: Define Character Areas and Transect Zones

• Walk the site and surrounding context (or analyze the masterplan if greenfield)
• Identify distinct character areas based on intended density, use mix, building scale, and street type
• Assign a transect zone (T1-T6) to each character area
• Document the rationale for each zone assignment
• Map zone boundaries on the regulating plan base (parcel map or block map)
• Ensure transitions are gradual (do not jump from T2 to T5 without intermediate zones)

Step 2: Assign Building Form Standards

• For each transect zone, calibrate the dimensional standards (height, setback/BTL, coverage, FAR)
• Select permitted building types for each zone
• Define building disposition (edgeyard, sideyard, rearyard, courtyard) for each zone
• Set ground-floor height minimums (especially for zones requiring commercial ground floors)
• Define step-back requirements for zones permitting buildings above 4-6 stories
• Specify tower controls (floor plate, separation, coverage) for T6

Step 3: Define Frontage Types

• For each transect zone, select the permitted and required frontage types
• Specify dimensions (depth, height, setback) for each frontage type
• Identify required retail frontage streets (where shopfront frontage is mandatory)
• Illustrate each frontage type with a section drawing and photograph (or described equivalent)
• Define the relationship between frontage type and the sidewalk/furnishing zone

Step 4: Create Thoroughfare Standards

• Classify every street in the plan area by type (boulevard, avenue, commercial street, neighborhood street, alley, etc.)
• Assign a cross-section to each street type (use the Street Design skill for detailed specifications)
• Specify ROW width, travel lanes, parking, bike facilities, sidewalk zones, median, planting, and lighting for each type
• Map thoroughfare types to the regulating plan

Step 5: Write Public Space Standards

• Identify all civic spaces in the masterplan (plazas, greens, squares, parks, playgrounds, community gardens)
• Assign a civic space type to each
• Specify minimum size, character, required elements, and programming for each
• Define the relationship between civic spaces and adjacent transect zones (e.g., a plaza must be fronted by T5 or T6 with shopfront frontage)

Step 6: Draft Regulating Plan

• Combine all layers onto a single regulatory map: transect zones, thoroughfare types, civic space locations, special district boundaries, required retail frontage lines, build-to lines
• The regulating plan is the applicant's primary reference -- it must be clear, unambiguous, and at a scale that shows individual parcels
• Include a legend that keys to the code text for all standards
• Provide both a full-area regulating plan and enlarged sub-area plans for complex zones

Step 7: Add Administrative Procedures

• Define the review process: by-right approval (administrative, no hearing) for projects that comply with all standards; design review (staff or board) for warrants (minor deviations); variance process for hardship cases
• Specify which deviations are warrants (minor, staff-approved) versus variances (significant, board-approved)
• Define the submittal requirements: site plan, building elevations, floor plans, landscape plan, signage plan
• Establish a pre-application conference process for large projects
• Include a nonconformities section (existing buildings that do not comply with the new code)

Step 8: Create Design Guidelines Companion Document

• Produce an illustrated, advisory companion document that shows the intent and aspirations of the code
• Include precedent photographs, rendered streetscapes, and annotated diagrams
• Cover topics that are difficult to regulate by code: color palettes, material quality, landscape character, architectural style compatibility
• This document informs applicants, guides design review, and builds community understanding
• Design guidelines are advisory, not mandatory -- they supplement the code but do not override it

6. Output Format

When producing a zoning analysis or form-based code, deliver the following specification package:

Zoning Analysis Output Template

SITE: [Address / Location]
EXISTING ZONING: [Current zone designation]
PROPOSED ZONING: [Proposed zone designation, if applicable]

DIMENSIONAL STANDARDS:
+-----------------------+----------+-----------+
| Parameter             | Required | Proposed  |
+-----------------------+----------+-----------+
| Max Height (stories)  |          |           |
| Max Height (meters)   |          |           |
| Front Setback / BTL   |          |           |
| Side Setback          |          |           |
| Rear Setback          |          |           |
| Lot Coverage (max %)  |          |           |
| FAR (max)             |          |           |
| Open Space (min %)    |          |           |
| Parking Requirement   |          |           |
+-----------------------+----------+-----------+

PERMITTED USES:
- Residential: [list]
- Commercial: [list]
- Institutional: [list]
- Other: [list]

BUILDING TYPES PERMITTED:
- [list with max dimensions for each]

FRONTAGE TYPES REQUIRED/PERMITTED:
- [list with dimensions]

SPECIAL CONDITIONS:
- [overlays, special districts, historic designations, etc.]

DEVELOPMENT CAPACITY:
- Lot area: [sqm]
- Buildable area (coverage): [sqm]
- Maximum floor area (FAR): [sqm]
- Estimated dwelling units: [range based on unit size assumptions]
- Estimated commercial area: [sqm, if applicable]

COMPLIANCE NOTES:
- [List any variances or warrants that would be required]
- [List any additional approvals needed (design review, environmental, etc.)]

Form-Based Code Output Template

FORM-BASED CODE: [Project / Plan Area Name]
JURISDICTION: [City, State/Province, Country]
DATE: [Draft date]
VERSION: [Version number]

ARTICLE 1: GENERAL PROVISIONS
- Purpose and intent
- Applicability
- Relationship to other codes
- Definitions

ARTICLE 2: REGULATING PLAN
- [Map with zone designations]
- Zone descriptions and intent

ARTICLE 3: BUILDING FORM STANDARDS
- [Table for each zone: T3, T4, T5, T6]
- Building type specifications
- Building disposition standards

ARTICLE 4: FRONTAGE TYPE STANDARDS
- [Table for each frontage type]
- Illustrations and dimensions

ARTICLE 5: PUBLIC SPACE STANDARDS
- [Specifications for each civic space type]
- Landscape standards

ARTICLE 6: THOROUGHFARE STANDARDS
- [Cross-sections for each street type]
- Intersection standards

ARTICLE 7: PARKING STANDARDS
- Parking requirements by zone and use
- Bicycle parking requirements
- Design standards for parking structures

ARTICLE 8: SIGNAGE STANDARDS
- Sign types by zone
- Dimensional standards
- Illumination standards

ARTICLE 9: ADMINISTRATION
- Review procedures
- Warrants and variances
- Nonconformities
- Definitions

7. Reference Links

Primary Standards and Model Codes

• SmartCode v9.2 (Center for Applied Transect Studies): https://transect.org/codes.html
• Miami 21 Form-Based Code: https://www.miami21.org/
• Denver Form-Based Code (Zone Districts): https://www.denvergov.org/Government/Agencies-Departments-Offices/Community-Planning-and-Development/Denver-Zoning-Code
• Form-Based Codes Institute (FBCI): https://formbasedcodes.org/
• Congress for the New Urbanism (CNU): https://www.cnu.org/
• Duany Plater-Zyberk & Company (DPZ CoDesign): https://www.dpz.com/

Supplementary Resources

• American Planning Association (APA) Zoning Practice: https://www.planning.org/zoningpractice/
• Lincoln Institute of Land Policy: https://www.lincolninst.edu/
• Urban Land Institute (ULI): https://uli.org/
• National Association of City Transportation Officials (NACTO): https://nacto.org/
• ITDP TOD Standard: https://www.itdp.org/publication/tod-standard/
• PlaceMakers Code Study Collection: https://www.placemakers.com/
• Project for Public Spaces (PPS): https://www.pps.org/

Foundational Texts

• Duany, Plater-Zyberk, Alminana. The New Civic Art: Elements of Town Planning. Rizzoli, 2003.
• Parolek, Parolek, Crawford. Form-Based Codes: A Guide for Planners, Urban Designers, Municipalities, and Developers. Wiley, 2008.
• Talen, Emily. City Rules: How Regulations Affect Urban Form. Island Press, 2012.
• Barnett, Jonathan. Redesigning Cities: Principles, Practice, Implementation. APA Planners Press, 2003.
• SmartCode Manual v9.2. Center for Applied Transect Studies, 2009.