Project: Tonalacalli custom home, Austin, Texas. Size: 3,082 square feet. Cost: $200 per square foot. Completed: June 2008. Certifications: LEED-Platinum, Austin Energy Green Building Program 5-Star rating. HERS Rating: 40. Architect: Environment Associates, Houston. General Contractor: Custom Building, Austin.
Austin, Texas’ first LEED-Platinum residence began with a simple request from the owners: a healthy house that would live in harmony with the land. The couple—he’s a geophysicist, she’s a biologist who grew up in Mexico—wanted to experience the low-impact pleasures of minimal energy bills, clean indoor air, and total reliance on rainfall for their household water needs. For a 34-year green building veteran like architect LaVerne Williams, AIA, LEED AP, it was a dream commission. Not only were the owners committed to making their home as environmentally friendly as possible, it was also an opportunity to work in a city whose builders are exceptionally well versed in sustainable materials and methods, thanks to Austin Energy’s venerable Green Building Program.
To Houston-based Williams, that difference is measurable. “The same house in Houston will cost twice as much as in Austin, because Austin’s electric utility is city-owned and they’ve been pushing the public to build green for almost two decades,” he says. “There’s an industry trained to deliver.”
Austin also delivers a mild climate and plenty of sunshine and rainfall. Williams’ design is a simple, common-sense response to the site’s microclimate using modern materials and technologies.
The house—dubbed Tonalacalli, which means “house of sun and water” in the ancient Nahuatl dialect of Central Mexico—is situated on 10 acres just outside city limits. Heating and cooling loads were minimized by orienting the house east-west, bathing the long south-facing front in sunlight while avoiding late-day heat gain from the west. Deep, shaded porches capture cooling breezes and add outdoor living space to the 3,082-square-foot house.
The need for air conditioning is delayed by two months, Williams says, thanks to north-facing operable clerestory windows in the master suite and the open-to-below second floor. When the windows are open, hot air is swept up through the clerestories and replaced with cooler air from the bottom of the house. “You have this Venturi effect creating the air flow, and also the heat stack effect with hot air rising,” Williams says. “It’s like having a whole-house fan.”
The house’s thermal mass also helps maintain comfortable indoor temperatures year-round. First-floor walls were built with 8-inch-thick aerated autoclaved concrete (AAC), a lightweight structural material with tiny insulating air pockets. In winter, the stained-concrete floor and AAC walls absorb and store the sun’s heat, moderating temperature swings by radiating it slowly into the home. The reverse occurs in warm weather, when the thermal mass slowly releases cooler nighttime temperatures throughout the day. This delays the need for air conditioning until nighttime, when the cooling load is lighter. Throughout the house, Energy Star–rated appliances and compact fluorescent bulbs also reduce electricity use.
With basic passive solar and energy conservation measures in place, Williams specified a 3.3-kWh photovoltaic array and a solar hot water system, which together provide for 80% of the house’s electricity needs. The 16 panels are mounted on the metal roof of a detached carport/greenhouse/workshop that faces due south. Linked to the house by a covered walkway, the 1,272-square-foot building has the added benefit of housing the mechanical equipment and offering ample space for more PVs down the road.
Most of the home’s materials came from Texas. The project earned four LEED points for its use of plentiful local wood species, including Eastern red cedar porch columns, ceiling beams and trim, interior stair handrails, and master-closet shelving; reclaimed long-leaf yellow pine second-story flooring; and mesquite bathroom cabinets, entry floor, and stairs. Balcony handrails and balusters were cut from juniper found on the property, and some of the stone used on the building base, walkways, and fence was excavated on site.
Four additional LEED points came from a rainwater harvesting system that captures runoff from 100% of the buildings’ roof surfaces—enough to supply all the water needed for drinking and household use. Rainwater is stored in two 10,000-gallon above-ground tanks, which sit about 50 feet west of the house, and is pumped through purifiers and into the house’s supply line. Wastewater is run through an on-site sewage treatment system and sprayed back onto the landscape.
For the couple, avid gardeners, living off the land also meant growing much of their own food. They installed a drip irrigation system for the vegetable garden, but the drought-tolerant ornamental landscape needs scant water. Conservation continues inside the house with Toto’s 1.1-gpf toilets and 2.2-gpm faucets.
Although green certification was never an explicit goal, Williams’ trademark environmental rigor paid off. Tonalacalli earned the Austin Energy Green Building’s 5-Star rating—the program’s highest—and the distinction of being the first LEED-Platinum home in the city.
As pleased as he is with the project’s outcome, Williams has his sights set even higher. “We’ve got to go beyond green, and beyond sustainable, to regenerative architecture,” he says.
Cheryl Weber is a freelance writer in Lancaster, Pa.
PROFILE:LaVerne Williams, AIA, LEED AP
LaVerne Williams takes a purist’s approach to sustainable building. In fact, he insists on using the term green to describe current projects, because it more accurately portrays an industry in transition. “I refuse to call projects ‘sustainable’ as long as fossil fuels are involved in the making and operation of buildings,” he says. “We’re in such a dire situation with climate change that we need to get our terms straight. As long as we mislead the public, the hard choices about true sustainability are not going to be made.”
Williams’ conservation ethic was instilled early in his life by his parents and community activities. He later spent 10 years learning the nuts and bolts of construction while working his way through the University of Houston’s architecture program. By 1975 he had launched the architecture firm Environment Associates, and a year later helped found the Texas Solar Energy Society and the Houston Solar Energy Society (now called Houston Renewable Energy Group).
Yet the Tonalacalli house is Williams’ first commission to include photovoltaics, a fact that reflects his focus first on passive solar design and energy conservation as the highest priorities, before adding PVs or active solar system features.
“Our work is about quality of life and looking at things holistically,” he says.
Wood-Burning Stove
A Vermont Castings DutchWest catalytic cast-iron wood stove (model 2460) contributes to heating needs and has a low EPA emissions rating of 1.1 grams per hour. The adobe hearth was crafted by ThangMaker Construction. Vermont Castings: 800.525.1898. www.vermontcastings.com ThangMaker: 512.517.9272. www.thangmaker.com
Flooring
Stained concrete floors in the living areas of the slab-on-grade house enhance passive heating and cooling. Cork flooring in the media room absorbs sound and is renewable, as is the kitchen’s Forbo Marmoleum linoleum and the bamboo in the master suite and study. The upper-story floor is longleaf pine reclaimed from a Galveston, Texas, warehouse by Hill Country Woodworks of Texas. Bravo Concrete Design: 512.331.4333. www.bravoconcrete.com Natural Cork cork and bamboo: 800.404.2675. www.naturalcork.com Forbo: 866.627.6653. www.forboflooringna.com Hill Country Woodworks: 512.756.6950. www.texaswoodwork.com
Interior Wall Finishes
Mud plaster for first-floor walls was made on site by ThangMaker Construction using raw clay from nearby Elgin, Texas, and locally sourced wheat straw. The upstairs drywall is covered with BioShield Healthy Living no-VOC paint. The natural clay coatings comply with Green Seal Standard GS-11 and come in a range of textures and tones. ThangMaker: 512.517.9272. www.thangmaker.com BioShield: 505.438.3448. www.bioshieldpaint.com
Windows
Double-pane aluminum-clad wood windows provide ample insulation in Austin’s mild winters. Williams chose casement, awning, and fixed windows to avoid the weather-stripping wear and tear on sliders and single- or double-hung units. These have a U-value of 0.47 and an SHGC of 0.46. The Pella Designer Series windows tilt down for cleaning. Operable clerestories provide additional daylighting and vent hot air. The awning clerestory windows are paired with an RC 312-S manually operated Window Wand from Miller Mfg. Pella: 800.374.4758. www.pella.com Miller: 707.584.9528. www.windowwand.net
Rainwater Collection
With no well or municipal tie-in, the water for the home is supplied entirely by rainfall using a Rain Man Waterworks system consisting of two above-ground 10,000-gallon tanks that store runoff from the metal roof. Water is pumped through a two-stage micron filter before passing through an ultraviolet purifier and into the house’s supply line. Wastewater is treated on site and sprayed back onto the landscape. 512.351.5150. www.rainharvester.com
Siding
Given the humid climate, the architect specified moisture-resistant fiber-cement materials from James Hardie for upper-story siding, trim, and soffits. The surfaces are finished with Duckback Woodperfect Series Semi-Transparent Coating, a locally sourced low-VOC stain. James Hardie: 888.542.7343. www.jameshardie.com
Walls
First-story walls consist of 8-inch-thick autoclaved aerated concrete block from Xella AAC Texas and the company’s proprietary stucco exterior finish. The blocks, which contain small air pockets, provide thermal mass and superior insulating values (R-18 in Austin). The concrete blocks emit no VOCs and eliminate the need for pesticides to control termites. On the upper story, 2x6 wood framing is sprayed with BioBased’s Greenguard-certified closed-cell polyurethane insulation foam. Xella AAC: 888.729.3552. www.xellatexas.com BioBased: 800.803.5189. www.biobased.net
Photovoltaics and Roofing
Sixteen Sharp modules deliver 3.3 kWh of electricity, and a Fronius IG inverter ties the panels to the grid. With the addition of a solar hot water heater from TechSun Solar, the sun supplies about 80% of the household’s energy needs. Sharp: 800.765.2706. www.solar.sharpusa.com Fronius USA: 810.220.4414. www.fronius-usa.com TechSun Solar: 866.765.2763. www.solarme.com The standing-seam galvanized metal roof lasts 40 years, about the life span of the solar arrays. Its U panels were made from readily available mill stock and crimped on-site. Deep overhangs protect doors and windows from the elements, reducing utility and maintenance costs.