continued

For qualification under the Built Green Colorado program, houses are assessed according to the specific criteria on the Built Green Checklist, which includes an energy efficiency requirement and a menu of "green" options. Qualifying houses must include at least a minimum number of these options. The range and number of options available on the checklist means each builder may build "green" a little differently.

Tierra Concrete Homes was the first certified "green builder" in southern Colorado. Their combination of passive solar design and insulated concrete construction has won many sustainability awards over the years, of which the Built Green Award for Tierra's entry in the 2001 Colorado Springs Parade of Homes is the most recent.

To facilitate bank financing for buyers, Tierra's insulated concrete houses look the same as conventionally framed houses. To ensure sales, they cost the same as well. The difference is their high-energy performance and low forest-product consumption.

Over twenty years ago Frank Fosdick, Tierra's project manager, invented a system of reinforced concrete panel walls for houses that minimize the use of natural resources in construction, operation, and maintenance.

Under this patented system, the walls are poured flat at the job site or on a casting bed at a manufacturing site. Electrical outlets and conduit, door, and window block-outs are embedded at the time of the pour. The wall panels are then hoisted into position by crane, and welded to a grade beam foundation. Assembly is swift, taking only one or two days.

The remainder of the construction process is conventional — with the addition that Tierra incorporates Built Green's checklist items into its conventions. These include heavy insulation, passive solar space and hot water heating, energy-efficient appliances and lighting, low-e windows, and sealed-combustion fireplaces.

Tierra's commitment to sustainable building also extends to teaching and marketing a variety of low-energy building technologies. The company's president, Judy Fosdick, has received special "hall of fame" recognition from Built Green Colorado for her long-term commitment to raising awareness of sustainability in the construction industry.

Lennar's Destiny

Each house that Lennar Homes builds in the state of Colorado meets the Built Green standards. Award-winning Model 8027 features an impressive list of about fifty "green" features, ranging from solar orientation to low-toxicity grout. Work begins by saving all site topsoil for reuse, and ends by providing the purchaser with a list of native, drought-resistant plants. In between, the builders incorporate environmentally sound practices into each aspect of the house's design and construction.

Improving a building's thermal performance is one of the most effective ways to reduce its environmental impact. To maximize passive solar heating from the Colorado winter sun, these houses are oriented with their long dimension facing within 30 degrees of south. Thermal performance is further improved with a sealed-combustion gas fireplace, sealed wood-burning fireplace, or woodstove using outside combustion air.

In addition to formaldehyde-free, recycled-content insulation within the wall cavity, the house uses R-3.5 exterior wall sheathing. Exterior doors (including the garage door) are insulated to R-5 or greater.

Choices of materials also bear out a commitment to sustainability. The house is designed to avoid using large-dimension solid lumber (2x10 or greater), and instead uses engineered wood I-joists for floors, and trusses or I-joists for roofs.

Sheathing and siding contain a minimum of 50 percent recycled fiber. And the framing system — including 24-inch-on-center studs in interior nonbearing walls, and three-stud corners — further reduces the use of wood in this house.

Roofing choices include concrete, slate, clay, metal, or fiberglass, for a guaranteed minimum performance of 30 years, reducing waste and maintenance costs over the building's lifetime.

Interior materials, such as low-VOC (volatile organic compound) paints and finishes, low-toxicity mastic and grout, and low-toxicity binders in recycled-content doors, improve indoor air quality for residents, while light-colored walls and carpets and the use of compact fluorescent light bulbs reduce the electricity needed for lighting.

During construction, more than 50 percent of job-site waste is recycled.

Perhaps most significant for the environmental impact of residential construction, the Lennar's Model 8027 house is not a singular success. As a mass-produced house, it implements these award-winning technologies and practices on a scale that make a larger difference.

Built Green Colorado is a voluntary program, which its creators believe to be the largest green building program in the United States. It promotes the use of building technologies, products, and practices that provide greater energy efficiency, reduce pollution, provide healthier indoor air, reduce water use, preserve natural resources, and improve building durability.

Katharine Logan is an assistant editor of ArchitectureWeek.

The living room of the Built Green award-winning house from Tierra Concrete Homes, Inc. is as cozy as a "stick-built" house. Photo: Tierra Concrete Homes, Inc. Building services are installed before the concrete pour with Tierra's patented construction system. Photo: Tierra Concrete Homes, Inc. Floor plans for the "Built Green Home of the Year over $500,000" from Tierra Concrete Homes. Photo: Tierra Concrete Homes, Inc. Tierra's kitchens have energy-efficient appliances. Photo: Tierra Concrete Homes, Inc. The concrete walls and floors act as a heat sink for storing the sun's heat energy in winter and keeping the house cooler in summer. Photo: Tierra Concrete Homes, Inc. Southwest view of the Tierra house at night. Photo: Tierra Concrete Homes, Inc.   Click on thumbnail images to view full-size pictures.