In January 2005, we announced the Dwell Home II Design Invitational, with the aim of establishing a model for sustainable home building in the 21st century. Intrepid Angelenos Glen Martin and Claudia Plasencia offered up their plot of land in Topanga Canyon as the test site. Escher GuneWardena Architecture was selected from a group of five architects to build the winning design: a 2,000-square-foot home with a budget of approximately $500,000 exclusive of land costs.

Unrelenting rains this winter caused delays in permitting, as several required tests were unable to take place. Escher GuneWardena thus turned their undivided attention toward one of the less glamorous but most critical components of making this house as self-sufficient and energy-efficient as possible: water usage.

The Metropolitan Water District of Southern California estimates that a family of four uses approximately 163,000 gallons of water a year. Supposing that 60 percent (98,000 gallons) of that water consumption is for the outdoors and 40 percent (65,000 gallons) is used indoors, low-water-usage plumbing fixtures and appliances should reduce indoor water use by about 25 percent (16,000 gallons). Understanding that decreasing the level of water consumption is key to the house’s sustainability, the architects devised a plan to separate and reuse the domestic graywater (from showers, washing machine, sinks, and dishwasher) both to irrigate the green roof and to flush the toilets. If the house’s toilet flushing accounts for about 6,800 gallons per year, utilizing graywater for this activity has the potential to reduce the indoor water use to 42,200 gallons a year.

“The environmental issues relating to the heating, cooling, and water management are some of the most interesting but highly complex aspects of this house,” explains Bojana Banyasz, the project architect. “Right now, the project is in a stage where most of the development is taking place on a more technical level in collaboration with our consultants.”

The first of these developments was deciding which septic system to use. The team opted to go with a MicroSepTec tank—a top-of-the-line septic treatment tank—and the architects devised a scheme that plants the tank under the future driveway. Cameron Church, a consultant from Los Angeles–based Environmental Planning and Design (EPD), explains that the septic system is crucial because “all the wastewater from the home will be treated onsite in a four-stage treatment process. There is no connection to a municipal sewer, which is important to making the project as green as can be.”

The treatment process (see illustration below), says Church, “comprises primary settling and anaerobic (without oxygen) digestion, two stages of aerobic (with oxygen) digestion, and ultraviolet light disinfection.

The treated, disinfected water will provide irrigation to the home’s planted roof and toilet water.”

Two seepage pits, where unused treated wastewater will be deposited, rest 6 and 16 feet, respectively, from the septic tank. A third seepage pit is at the southwest corner of the house. This pit will collect the water runoff from the roof, since the county requires that any treated water, even if it’s only irrigating the roof, must be collected to avoid possible contamination of the surrounding land.

According to Church, “Any extra water from the roof’s irrigation will gravity flow into the seepage pit [see illustration, page 116] on the south side of the house, from which it will percolate into the ground. In rainstorms, the first inch of overflow from the roof will also be directed to the seepage pit.” Architect Frank Escher says, “As far as we know, this type of system has not been attempted, at least not on the residential scale and certainly not in Topanga Canyon. So it’s really a learning process for us all.”

Part of building a good structure is building a good team and, as Ravi GuneWardena explains, “EPD are experts in sustainable water systems and solutions for environmentally friendly buildings. They were consultants for the Audubon Center in Los Angeles and the Natural Resources Defense Council regional office in Santa Monica, both LEED Platinum-certified green buildings. We’re very happy that they’re on our team.”

After reaching agreement on the direction of the water treatment, drills were called in to conduct the necessary percolation testing of the seepage-pit sites. With the tank installed, the home site is ready for further surveying in preparation for groundbreaking in early 2006.