The Batesville Net-Zero Home

The architecture of the Batesville residence was inspired by the clients’ love for Frank Lloyd Wright’s Usonian houses and their wish for a contemporary design that integrated energy-efficiency and sustainable materials with warmth, sensually interesting textures, variety in spacial experiences, and good indoor-outdoor connections and views to the surrounding Virginia Piedmont and Blue Ridge Mountains.

Through multiple design-, energy-modeling-, and budget iterations, it became clear that the priority with respect to energy was to be net-zero or even net-positive through integration of solar power, rather than seeking passive house certification. Therefore, in team with our builder, Daniel Ernst of Promethean Homes, we settled on a building envelope that is well-insulated, vapor-open and air-tight, and relatively affordable with about 1/3 less in average R-value than would have been needed to meet passive house heating demand criteria. While the initial goal was net-zero, the clients reported a net-positive energy status after a year of residence.

The basement walls are insulated concrete forms (ICF) finished in stucco; the above-ground walls are advanced framing wood stud walls with dense-packed cellulose between the studs and exterior rigid rockwool insulation for a thermal-bridge-free construction. The exterior walls are clad with thermally treated wood and corten steel rainscreen siding. The windows and doors are european triple glazed, wood-aluminum clad tilt & turn windows, providing excellent energy-efficiency, durability and functionality as well as great daylight and views. These ‘passive measures’ are complemented with an ‘active system’ of a 7.2kWp photovoltaic array that feeds off the grid if there is an energy surplus, and once a battery bank is added, will also supply the house with power during power outages. Currently the inverter provides a small amount of power, enough to keep the refrigerator running during an outage for example. The clients plan to install lithium-ion batteries in the near future to allow for a larger load and multiple days of off-grid power supply. The supplemental heating and cooling is provided by two 1t ducted mini-split heat pumps and a wood-stove with direct air-supply and a sealed combustion chamber.

Beyond the envelope, the architecture integrates basic principles of energy-efficient and sustainable design: overhangs on three sides to provide shading in the summer and protection from weather, large openings in the south to allow for passive solar heat gains in the winter, and low and high openings in the north to provide passive cooling and glare-free daylight and support cross-ventilation. Additionally, insulated, exposed concrete floors in the basement and in the slab-on-grade portion of the house serve as thermal mass to help cool in the summer and to store the warmth of daytime sun in the winter.