Plenty of thermal mass, deep porch overhangs, and quality windows help this Texas Hill Country house keep its cool during sultry summers.
When Laurel Treviño and husband Carlos Torres-Verdin moved to Austin in 1999, southwest Austin was still “in the country.” Not anymore. But in an area exploding with “little boxes” organized in subdivisions, their home stands out as a more sustainable model.
Treviño had nursed the dream of building a green house for three decades, influenced by books like The Barefoot Architect, and inspired by outings to rural “eco-homes.” It was on a Cool House Tour that the couple met architect LaVerne Williams and learned about Hebel aerated autoclaved concrete (AAC) blocks. Treviño originally wanted to build with straw bale or adobe, but decided against these materials because of the labor involved.
One of the first Leadership in Energy Efficient Design (LEED) certified homes in the nation, Tonalacalli (“house of sun and water”) uses passive and active solar, insulation, thermal mass, and quality glazing to achieve its energy efficiency. A 3.3 kW batteryless grid-tied PV system offsets almost of the home’s electricity, and a two-collector solar hot water system provides most of their water heating. The AAC blocks balance thermal mass and insulation, decreasing temperature swings inside the home. Deep porches and eaves help keep the hot summer sun at bay, while well-placed operable windows funnel summertime breezes through the house, reducing the couple’s reliance on mechanical cooling. Despite the legendary Texas summers, they use their air conditioner only intermittently in the summer months, and rely on ceiling fans, and cross and stack ventilation to cool the home. During colder months, passive solar lowers the heating demand.
The house is not connected to city water and there’s no well; instead, 5,500 square feet of roof feed rainwater to three 10,000-gallon cisterns. Treviño says several of their neighbors have rainwater collection systems, too, in part because wells are drying up and droughts are severe and unpredictable.
Tonalacalli features local materials, from the clay plaster to the exterior stonework. Much of the interior wood came from trees on-site. Peeled eastern cedar logs formed the exposed columns; stair risers were crafted from local mesquite; stair railings, fencing, and decking came from mountain juniper harvested on site.
Tonalacalli has been featured on both the Cool House Tour and the Hill Country Tour; the couple also host many informal groups, including teachers and journalists. Despite the awards and accolades, Treviño insists the house could be even greener. If she could do anything differently, she would have built a smaller house, and built it out of Hebel block exclusively.