Subdivision Design

Converting Raw Land into Saleable Lots and Desirable Communities

Today’s Agenda

• What is a subdivision?– Regulatory requirements– Qualitative standards

• Subdivision layout process

• Design concepts

• Case study example

What is a subdivision?

• Conversion of a land parcel from its natural or previous state to:

• Legal entity, where lot ownership can be transferred

• Profit venture, where development costs can be recouped through lot sales

• Urban place, where neighborhood roots can be developed

Each Lot Must Have:

• Minimum size (sq. ft.)

• Minimum road frontage

• Provision for utilities– Water/sewer or well/septic– Electricity, phone, gas, cable, etc.

• Buildable area/feasible structure location– Meeting setbacks, buffers– Respecting constraints (slopes, soils, wetlands)

Subdivision Approval Process

• Sketch plan review– Feedback on type (major/minor), regulatory fit

• Preliminary plat review– Checks on roads, utilities, lots, etc.

• Final plat submission– Install improvements or post bond– Recorded in land and tax records

Sketch Plan

Preliminary Plat

Final Plat

What is a Good Subdivision

• Creates desirable social patterns

• Respects natural environment

• Provides efficient utility services

• Ensures accessibility (car, bike, pedestrian)

• Builds safe roads

• Minimizes cut and fill

• Seeks pleasant aesthetics

Elements of Success: 3 Scales

• Housing cluster or block – Access, parking, yards

• Neighborhood– Road systems– Open space network

• Community– Connectivity– Activity centers

Building a Sense of Place

• Theme or big idea (e.g., walkable neighborhood)

• Amenity location (e.g., central park, pool)

• Unique landscape (e.g., native plants, oaks)

• Architectural style (e.g., neotraditional)

• Site graphics (e.g., entry sign, st. signs)

Central Commons as a Big Idea

Subdivision Layout Process• Regulations (density,

lot size, open space, utilities, etc.)

• Average/minimum lot sizes

• Site analysis• Road access• Internal roads (topo,

block layouts)

• Lot layout (rectangles, short side to st., build. area, n/s orientation, no double frontage)

• Open space, amenities• Paths, sidewalks• Utilities/storm water • Vegetation & slopes• Refine alternatives

Open Space Subdiv. Design-1

• Identify open space areas– Primary conservation: wetlands, floodplains,

steep slopes– Secondary conservation: sensitive, scenic,

unique uplands

• Locate house sites– Maximum view lots, abut open space, min. lot

width

Site Before Development

Traditional Yield Plan

Primary Conservation Areas

Secondary Conservation Areas

Open Space Subdiv. Design-2

• Design road & trail alignments– Level or rolling areas– Avoid wetlands, habitats– Minimize road length, cost, dead ends, long

straight streets

• Draw in lot lines– Use off center, up front houses for larger side &

back yards

Adding Houses, Roads, Trail

Adding Lot Lines

Subdivision Street Concepts

• Curvilinear: naturalistic, organic– Source: Frederick Law Olmsted– Auto oriented street standards– Examples: Treyburn, Gov. Club, The Oaks

• Neo-traditional: geometric, grids, diagonals– Source: Andres Duany, Peter Calthorpe– Pedestrian/transit/auto networks– Examples: Seaside, Washington, South. Village

Subdivision Street Concepts-2

• Urban cluster: geometric, central courts– Source: Clarence Stein, Henry Wright– Separation of auto service lanes & pedestrian

paths and open spaces– Example: Radburn, N.J.

Curvilinear, Grid, & Cluster

Basic Housing Layout Concepts

• Single family detached &/or attached– Block: face street, w/ alleys (5-10 du/ac)– Cluster: face st. or green, w/ alleys (4-6 du/ac) – Parking court: face court (10-12 du/ac)– Eyebrow: face island (3.5-6 du/ac)

• Multi-family– Quadrangle: face court & parking (14-16 du ac)– Parking court: face parking (15-18 du/ac)

Block Layout

Cluster Layout

Parking Court Layout

Eyebrow Layout

Multi-family Quadrangle

Multi-family Parking Court

Case study example

• Difficult hilly site

• 1st layout disregarded drainage ways, slopes

• 2nd layout left drainage ways open, followed natural contours with road

Case Study Site Analysis

Original Plan--Too Costly

Better Plan: Respects Contours