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TechPractices: Island Presentation Partnership, Dewees Island, SC

 

TechPractices are outstanding housing projects throughout the U.S. where innovative technologies are implemented. Builders and remodelers can use these examples as models for projects of their own.

Island Presentation Partnership Snapshot
Location: Dewees Island, South Carolina
Builder: Island Preservation Partnership
Project Scope: 150 homesites for single-family detached permanent and vacation residences; 32 homes built, 1,600 to 5,000 sf, average 3,000 sf.
Price: Homesites $320,000 to $850,000; furnished homes $895,000 to $1,125,000
Financing: For-profit development
Innovations: Conservation in land use, passive climate design, SIPs, shared wastewater treatment, small-diameter sewer lines, rock filters, Energy Star appliances, low-VOC finishes and adhesives, low-flow plumbing fixtures, rainwater harvesting, permeable pavement, electric vehicles, xeriscaping

Summary

Dewees Island

Can profitable development be not only harmonious with the environment but actually enhance it? John Knott of Dewees Island thinks so. Claiming that "the environment and development are natural allies," he set about developing an island protected by conservation law. Combining local climatic responses with new materials, Dewees Island contains a growing population while protecting its sensitive ecosystems.



Details

drawing of house
view of house

When the development company, Dewees Island (DI), set out to develop the island, located 10 minutes by ferry from the mainland and 12 miles northeast of Charleston, they found a natural area with just three existing homes. About 65% of the scenic barrier island is set aside for permanent conservation by law. So DI started with an inventory of the island's natural resources (wind, vegetative covering, topography, orientation, and view), believing that harmonizing with them would reduce construction and maintenance costs.

With seven geological zones on the island, it was decided that all houses would be in the sturdiest zone, buffering the homes from storm surge while preserving the more sensitive areas. Dune fences (like snow fences), measures for new vegetative rooting, and beach access paths, are created to deter eventual erosion, common to many beachfront properties. In this case, dispersed home sites were determined to be less disruptive to the wildlife zones than clusters. DI asserts that this measure, together with creating additional ponds, triples the water habitat. And by limiting development to 150 homesites at two acres each, effectively 92% of the island is conserved, far less than the 65% conservation law. This leaves more vegetation to absorb massive rains, protecting against flooding.

For the building systems themselves, the designers relied heavily on industry information from DOE, Energy Design Update, Environmental Building News, and the Rocky Mountain Institute. A vertical, closed loop geothermal heating and cooling system was chosen for many of the homes, and the geothermal company assisted in energy modeling.

Passive solar climatic design figured largely in the initial planning stages of the community, and the architect was required to do a study of the sun and prevailing breezes for all four seasons. By orienting the houses to collect cooling breezes and incorporating deep overhangs and vegetation for shading, the air conditioning load could be reduced, saving construction and energy costs. The tight structural insulated panel walls and roofs, coupled with high-performance windows on the south and west sides, save additional energy. Transom windows in the interior walls enhance cross ventilation. The net result of these measures is that the homes are often cooled with ceiling fans.

The choice of wastewater treatment can be either a boon or a barrier to sustainability. If conventional methods were used, the leaching fields alone would take up much of the space set aside for houses. The difficult site conditions meant that a large number of lots couldn't even get a septic system permit.

To reduce the size of the treatment areas while still protecting the groundwater, the health department worked with the developer to design a system in which a combination of technologies was employed. Each residence has a septic tank/rock filter pretreatment system that feeds into a small-diameter pressurized sewer line, leading to a central disinfectant area, and finally a shared absorption field Shared Wastewater Treatment Systems. To regulate the amount of effluent going into the soil, a below-ground tank holds disinfected effluent, which is pressure-dosed to the absorption field. By these treatment methods, the entire absorption field for 150 houses is kept to 100 feet by 700 feet. A single absorption field is much easier to monitor for quality than many scattered fields.

Areas around the homes xeriscaped with native plants require little fertilizer or watering. This not only reduces maintenance and protects groundwater supplies but also allows efficient low-drip irrigation to be used, from harvested rainwater. High-efficiency dishwashers and horizontal-axis clothes washers save additional water and heating energy. All the appliances in the homes meet the EPA Energy Star Rating. Rounding out the water conservation aspect with low-flow plumbing fixtures, these homes use 70% less water than comparable homes.


Installation/Construction

Although Dewees Island includes its own construction outfit, Dewees Builders, home site buyers are permitted to hire any architect and builder they want, as long as resource-efficiency guidelines are followed. Buyers are encouraged to choose from Dewees' approved list of architects and suppliers if they choose not to go with some variation of the official Dewees Island Home.

Construction crews are trained in waste reduction. Lumber is minimally cut, and scraps from lumber and pilings are used as landscaping posts and mulch. This reduces both landscaping and carting costs. In areas of the walls and roof in which air gaps have been created during construction, an expanding spray foam is added to stop air infiltration.


Benefits/Costs

With oceanfront property in South Carolina at a premium, the home sites are fetching $325,000 to $850,000. Fully furnished Dewees Island Homes go for $895,000 to $1,125,000. These prices reflect the market more than the cost of building in environmental performance. DI actually saved money with environmentally benign practices, enriching an already profitable venture. For example, the decision to cut back paving reduced other costs including storm water drains and regional ponds. And mounting outdoor lighting on existing trees eliminated the need to clear them and install massive lampposts. Although monthly bills are not the first concern of these homeowners, efficiency measures yield 60% energy savings, 70% water savings, and 60% household waste savings. Dewees Island Homes are built to exceed Energy Star standards.


Code/Regulatory

Barrier islands typically present difficult wastewater problems with their fragile, sandy soils and high water tables. The nearby shellfish waters posed a particularly delicate situation. Before the state Department of Health and Environmental Control (DHEC) issued a variance for the space-saving wastewater treatment system, the developer went through a period of groundwater monitoring. Still, the DHEC mandated the absorption field be at least 4' above the water table. This and the high water table in the island required a mound absorption field, built 10 feet above sea level. This required filling and grading, adding costs.

Water transportation is a way of life at Dewees. But the extensive sitework needed for private docks would close shellfish hatcheries. A community docking design was much less disruptive, but only approved for commercial facilities. So another variance was sought and approved.

To ensure future preservation and resource efficiency, Dewees Island established its own architectural and environmental guidelines. For example, every plumbing fixture in every building has to be low-flow, and any watering of vegetation must be drip irrigation via cistern. Kitchen wastes are composted and garbage disposals are prohibited. Individual homes are limited to 5,000 sf. There is an absolute island limit of 150 homes.


Feedback

The development is meeting sales expectations. In Fall 1996 there were 15 residences built on the Island, with 10 to 12 more expected the following year. As of Fall 1998 there were 32 homes built, with eight more in various stages of design and construction. At this rate, home sites are expected to sell out in two years. According to the developer, the buyers appreciate the beauty and tranquility of the place, and feel they have a personal stake in its preservation.

Developers attribute the Island's success to an exclusive, but wide-ranging, marketing campaign. The approach is described as more personal and one-on-one, directed at a buyer with an environmental ethic. Ads are placed in specialized publications, and a substantial response has come through the company website. Additional interest is channeled through local realtors and friends of current Dewees homeowners. And a certain amount of P.R. is generated through the enthusiasm of John Knott, the company's CEO and managing director, who travels extensively to give talks about the project and related development issues.


Contact(s)

Do you have a specific question? Try the contacts listed below:

Dewees Island
46 41st Ave
Isle of Palms, SC 29451-2662
843-886-8783
www.deweesisland.com

Burt, Hill Assoc.
1056 Thomas Jefferson St., NW
Washington, DC 20007
202-333-2711
www.burthill.com

EPA EnergySTAR
Mailbox 6202 J
Washington, DC 20460
888-STAR-YES
www.energystar.gov/

Environmental Building News
28 Birge St.
Brattleboro, VT 05301
802-257-7300
www.ebuild.com

Energy Design Update
Cutter Information Corp.
37 Broadway, Ste. 1
Arlington, MA 02174-5552
781-641-5118
www.cutter.com/

Rocky Mountain Institute
1739 Snowmass Creek Rd.
Snowmass, CO 81654-9199
970-927-3851
www.rmi.org