Pueblo, Colo.-based Tierra Concrete Homes has taken precast wall construction one step further than commercial homebuilding. The company's homes have an insulation method that, combined with Tierra's design strategies, help reduce the homes' heating and cooling requirements as much as possible.

In developing the wall design, the company incorporated a strategy that combines passive solar design with thermal mass construction. According to Tierra Concrete Homes President Judy Niemeyer, the company has obtained design analysis from the National Renewable Energy Laboratory (NREL) and participates in NREL's Exemplary Buildings Program.

Tierra's unique tilt-up concrete construction method for precast walls involves insulating the walls and the foundations. Polyisocyanurate insulation forms the base of the exterior wall form. This insulation is secured to the outside surface when the walls are poured with connectors 16 in. on center. The company uses a frost-protected shallow foundation that is 2-ft. deep with 2 in. of rigid insulation around the outside perimeter of the concrete. Tierra places extra emphasis on using special insulation.

According to Niemeyer, Tierra has a patent application on this wall method, and the company licenses and trains other builders to use this system. The walls are poured horizontally, so they can be as little as four inches thick without sacrificing strength, says Niemeyer. Tierra constructs the walls at its precast manufacturing plant in Pueblo, and transports them to the building site intact. This insulated wall method, combined with solar design strategies, keeps the homes cool in the summer and warm in the winter. During the winter, the insulation on the outside surface traps solar gains in the walls. In summer, the walls absorb heat from the room during the day.

As a member of the Passive Solar Industries Council, Tierra has computer programs to assist in the design and analysis for energy efficiency. The passive solar design methods used by Tierra in addition to the insulation mostly involve strategic placement of the homes' windows. The number of south-facing windows are increased to gain direct sunlight in the winter. To accomplish this, Tierra selects the site and orients the building so that the long wall of the home faces south. Proper sizing and placement of north, east, and west windows and design of overhangs on the homes provides shading from the summer sun.

Landscaping also plays a role in the solar design, and Tierra makes recommendations to customers on specific tree and shrubbery locations that will help protect the home from winter winds. On the home's interior, the company designs the walls and windows to provide enough natural daylight so that occupants can use any room during the day without having to turn on a light, Niemeyer notes. The interior space has an open floor plan to allow air to circulate freely; this floor plan also allows the sun to penetrate deep into the house in the winter.

Tierra raises an average home in one or two days, according to Niemeyer. To prevent thermal short circuits, the company insulates the joints with 2-in. rigid foam and fills any cracks with spray foam. The partition walls between the rooms are also concrete, with the exception of the plumbing walls, which allow for pipes.

The remainder of the home is generally conventional, with wood trusses, a stucco exterior and drywall ceilings. Sometimes Tierra negotiates an "owner finish" agreement, with Tierra providing the enclosed shell and the homeowner finishing the interior.

Tierra homes are typically three-bedroom, one-story ranch-style houses with about 1,500 sq. ft. of living space. Because the company is an Energy Star Builder (affiliated with the Environmental Protection Agency's Energy Star Program), its homes qualify for Energy-Efficient Mortgages. These mortgages give home buyers access to a lower interest rate, lower closing costs and allowance for higher debt-to-income ratio, officials note.

These homes are cost-competitive with custom homes constructed with conventional techniques, Niemeyer says. Costs for insulation (roof, wall and full slab) and for the concrete walls are higher than equivalent costs in typical wood-framed construction, but there are significant savings from reduced construction time, limited drywalling and the elimination of central heating or cooling systems. According to Niemeyer, Tierra's home building system was evaluated by NREL and found to be 75 percent more efficient than the Model Energy Code. In addition, the company has received the National Association of Home Builders' National Energy Value Housing Award for two of its homes that were honored for being the most energy efficient in the Colorado climate.