To the east of Eagle Mountain Lake near the town of Lake Worth, Texas, Ferrier Custom Homes is putting the finishing touches on its first net-zero energy residence. The two-bedroom, two-bath, 1,051-square-foot house, dubbed the Zero-Energy Casita, will serve as a second home for its owners and will provide for much of their energy needs with a residential wind turbine.
Ferrier, which built the first LEED Platinum home in Texas and was named the NAHB's 2007 Green Builder of the Year, has focused on building sustainable, high-performance, and near-zero energy homes almost since its beginnings in 1984. More recently, company president Don Ferrier decided that every home he builds will be certified under LEED for Homes, the National Green Building Standard, Energy Star, the DOE's Builders' Challenge, and Green Built Texas. The casita in Lake Worth will follow suit.
Designed by Bundy, Young, Sims & Potter of Wichita Falls, Texas, the casita (Spanish for "small house") is an L-shaped ranch built of SIPs and lots of reclaimed wood. Its location in a category 2-3 wind zone provides ample opportunity for electrical generation, and luckily there is no homeowners association to restrict use of wind power. In fact, notes Ferrier, within about 1 mile of the casita are at least five other wind turbines.
Ferrier's strategy has long been to maximize a structure's energy efficiency before adding renewable energy generation, and his approach was no different with the Zero-Energy Casita. The house is oriented to take advantage of a 30-foot-tall oak tree and a stand of 20-foot-tall shrubs for shading. Solar heat gain is further minimized by the light-colored Galvalume metal roof installed over an airspace, which prevents up to 95 percent of the sun's heat from penetrating into the attic space, according to Ferrier. Weathershield ZoE5 windows and the SIP wall and roof deck construction create a well-insulated and tightly sealed envelope. To further conserve energy, ductwork for the highly efficient HVAC system runs through the conditioned attic space.
Ferrier and his consultants performed a lot of energy modeling before systems and R-values were finalized to maximize benefit and return on investment. In preliminary testing with its finalized systems, the casita scored a 30 on the DOE's E-scale (similar to the HERS scale). Once the structure's efficiency was assured, Ferrier and the clients decided on a 3.7 kW SkyStream wind generator, which has curved blades to minimize troublesome noise during operation.
When the wind generator produces excess electricity, it will feed back into the local power grid, and when the winds don't produce enough energy to operate the house, it will draw energy from the grid.
"Some people think wind turbines are unsightly, but if they're giving you zero energy they look pretty good to me," Ferrier says. He adds that the ideal renewable energy system is a combination of photovoltaics and wind, but the Zero- Energy Casita is so efficient and will be used about one-third of the year that only wind generation is necessary. The wind generator came with a $16,000 up-front price tag, but that will be offset substantially by local and federal rebates and tax deductions.
At a cost of roughly $200 per square foot, the Zero-Energy Casita may leave the wrong impression on those interested in zero-energy building but concerned about the cost. Performance is primarily achieved through passive measures and use of highly efficient systems and materials that do add some up-front cost but also provide cost savings over time. Much of the casita's price tag—as with the average custom home—is due to its finishes and the owners' desire for perfection.
Its rustic appearance looks simple, but results from extensive (and not inexpensive) use of antique reclaimed wood siding, wood flooring, and wood beams. "The owners wanted the house to look like it's been there 150 years," Ferrier says. "So it's both new and old." Interiors are finished to look like structural timber framing, with reclaimed 8x8 barn beams cut in cross-section and applied to the walls and ceilings along with a lightly hand-troweled wall surface to create a decorative façade. An additional 336 square feet of porch space, built with salvaged cedar from the site, expands the casita's living area to the outdoors.
Other green features include rainwater catchment for irrigation, xeriscaping, dual-flush toilets and water-conserving showers, and non-VOC and formaldehyde-free finishes, adhesives, and countertop materials. During construction, all scrap wood was ground up for mulch and scrap wallboard was ground and used as a soil amendment.
In a few years, the owners will use the casita as a guest or mother-in-law house, and they will build a larger, more permanent home on the site that also will aim for zero-energy performance.
Ferrier Custom Homes is tracking the Zero-Energy Casita's progress on a dedicated website that details all the house's features and discusses its sustainable materials and wind energy system.