After Will Rosenzweig and Carla Fracchia bought this 100-year-old farmhouse in Healdsburg, California, they hired Arkin Tilt Architects and Earthtone Construction to make an eco-friendly example out of it. The house had good bones but it was "thermally challenged in both summer and winter," says architect Anni Tilt. Thanks to the addition of a new wrap of rigid insulation on the exterior, new windows throughout, a ventilated roof, and a new wing with shade overhangs, the house is transformed. "It now provides an entirely different level of comfort and performance—a quantum leap forward—which has transformed the way we use it," the owners report. Click through the slideshow to see how the architects and contractors turned the old and leaky structure into a model of energy-efficiency. All photos courtesy of Edward Caldwell (copyright 2011).