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Open Space Residential Design (OSRD)
Case Study

Bellingham locus map Woodbury Ridge, Bellingham, MA

Woodbury Ridge is an excellent example of an Open Space Residential Design (OSRD) development that incorporates Low Impact Development (LID) practices. Homes are clustered, linear feet of roadway is reduced, drainage goes into slightly pitched open drainage swales, and rooftop drainage also goes into swales thus eliminating stormwater drainage infrastructure.

Designed by Weston & Sampson, Inc., the Woodbury Ridge project placed all housing units on the southern portion of the site where there was already substantial site disturbance. This environmentally-friendly housing project did not interfere with existing wetlands or intermittent stream crossings, provided new preserved open space for the town, and reduced overall costs for the developer, David Lachance of Bel Air Gardens, Inc.

Convential subdivision plan

Photo provided by Weston & Sampson, Inc.

A conventional subdivision plan for Woodbury Ridge.

OSRD Site Design with LID Techniques:

Under existing zoning regulations in Bellingham, the developer could have built a conventional residential development with twelve one-acre single family house lots and a total of 68,800 square feet of roadway paving that included 2,700 linear feet of roadway, two 40 foot radius cul-de-sacs, and 20 to 100 foot long driveways. Besides the overall impact of the houses and pavement, as conventional subdivision project it would have required one stream crossing, the filing of 1,500 square feet of wetlands, and 3,000 linear feet of piped drainage infrastructure which would have been both costly to install and to maintain.

Instead the Town of Bellingham, developer David Lachance, and site designers/engineers at Weston & Samson, Inc. designed an OSRD residential development. Their plan clustered the homes on 6 acres and preserved aesthetic natural landscape as permanent conservation land on 10.4 acres. They further reduced negative environmental impacts in the built land areas by incorporating LID practices into the subdivision. Instead of twelve one-acre lots allowed by right under Bellingham's zoning, the OSRD development created six smaller duplex lots ranging in area from .49 to .60 acres. A Homeowners Association was created to govern issues related to waste water, stormwater, and common lands.

OSRD plan with duplex lots

Photo provided by Weston & Sampson, Inc.

Alternative residential development plan with duplex lots and LID conservation techniques.

Equally important to reducing the ecological impact of the project is that fact that the impervious roadway surface area was reduced by 50 percent and infiltration of rainfall was greatly increased. Two catch basins were installed but virtually all piped street drainage was eliminated instead using open drainage (roadside water quality swales) at 2% pitch with no crown to handle roadway drainage and allow runoff to slowly infiltrate into the soil. Impervious pavement was reduced to 45,400 square feet with 1,700 linear feet of 22 foot wide roadway and 500 linear feet of 16 foot wide one way loop roads. Pervious pavement (Grasspave2) was installed in twelve overflow parking spaces instead of 2,200 square feet of impervious pavement.

In addition to concentrating most of the construction in previously disturbed areas of the site, the six-acre OSRD development reduced the subdivision area by 100 percent. The Town and its residents gained 10.4 acres of protected natural land. Wetlands on site were protected by 50 to 100 foot natural vegetated buffers.

Benefits for the Town of Bellingham:

Street cross section drawing

Drawing provided by Weston & Sampson

Street cross section plan.

With this development, the town will receive a host of environmental and municipal benefits. The natural hydrologic cycle and the base flows of local streams and wetlands will be maintained. Most of the stormwater will run into swales and slowly percolate through the soil recharging aquifers and augmenting groundwater supplies. The swales will collect, briefly store, and slowly release stormwater so the soil can "pre-treat", removing pollution and particulates present in runoff. This will reduce the amount of runoff and sediment that would otherwise enter the public drainage system thereby lowering the municipality's cost for maintenance and replacement of aging or damaged infrastructure.

Grasspave cutaway

Photo provided by Grasspave2

Cutaway of Grasspave2 structure.

By concentrating the homes on part of the site and creating natural vegetative buffers, abutter privacy will be enhanced. On-site natural areas with unique or fragile habitats will be preserved and protected. Residents will be able to easily access both neighbors and wildlife habitats through an interconnected network of trails and open space.

Benefits for the Developer and Realtor:

The OSRD development plan for Woodbury Ridge gives benefits to the developer and realtor too. Valuable amenities such as access to trails, views to open space, and privacy from abutting properties can enhance marketing of homes and their selling prices. Developments designed with nature can enhance aesthetics and home values. Homes in OSRD subdivisions have shown to appreciate faster than those in conventional subdivisions and remain attractive to buyers.

The developer benefits when the plan review process is streamlined which reduces time and costs. Designing with existing features of the terrain further decreases site development costs. Low impact development practices cost less than conventional drainage techniques to build and maintain due to a reduction in the size and number of detention facilities and the size and cost of pipes and drainage infrastructure.

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