Green and Gray Greenfab reuses rain water and treats graywater. The system includes a rain garden and three bioretention basins.

Green and Gray Greenfab reuses rain water and treats graywater. The system includes a rain garden and three bioretention basins.

Credit: Courtesy Greenfab

Outside the Box

A prototype Seattle home offers an unusual gift: graywater recycling.

Greenfab’s premier prefab house took three-and-a-half months to build: 14 days in the factory, one day to install, and three months to finish. But the business model was years in the making. The goal: to create a house that is healthier, stronger, and more energy efficient than its stick-built counterparts. “Ours may have a similar sales price to other new homes on the block, but it offers more value in energy efficiencies and innovation,” says Greenfab founder Johnny Hartsfield.

One of two models the company sells, this one is owned by Robert Humble, principal of the Seattle firm HyBrid Architecture, who developed the designs and studied their adaptability to different sites. “It was a good opportunity to get Greenfab’s business off the ground,” Humble says.

And to influence the state’s residential building code. The pilot graywater loop Humble and Hartsfield developed is the first of its kind for a Seattle home. A 1,400-gallon cistern captures rainwater from the roof for landscape irrigation, toilet flushing, and laundry. The used water from bathroom sinks, laundry, and showers passes through a filter and into three 300-gallon bio-treatment basins in the backyard. Any overflow gushes into a rain garden and percolates back into the ground. “It passed inspection, and we’ll finish it once the new code is adopted,” Humble says.

The 1,790-square-foot, three-bedroom house is also extremely efficient. Exterior walls (R-26) are covered in rigid insulation and spray foam. A hybrid water heater supplies hot water, and a mini-split heat pump takes care of heating and cooling. There is also pre-wiring for a 2.4-kW PV system—enough to offset a quarter of the energy use.

If modular construction is all about control, so are snazzy details such as the TED 5000 energy monitor. “You can access it on an iPad or phone and adjust your usage if you want to hit targets,” Hartsfield says. “It’s easy to monitor on the go.”

Now developing partnerships with factories and builders across the U.S., Hartsfield believes prefab is a good delivery model for today’s carbon-neutral goals. Humble thinks so too. “Houses are becoming more sophisticated from an energy and mechanical perspective, and harder to build,” he says. “A factory can easily accommodate those requirements.”