Serenbe Residence

Just outside the metropolitan hum of Atlanta in a pioneering community of EarthCraft-certified homes called Serenbe, Luis Imery is building the area’s first ProudGreenHome net-zero residence. The 1,400 acres of this sustainable development feature 120 homes with 300 residents and several homes targeting net-zero-energy status. Imery, however, wanted to “blow everyone’s mind in terms of performance and aesthetics.” His cutting-edge 2,600-square-foot home, which will be offered at a lower price point than other Serenbe homes because of its size and energy efficiency, was completed in June 2013. By then, Imery had already been asked to build a second home in Serenbe.

Curb Appeal

When local advocacy network ProudGreenHome approached Imery’s company, Imery Group, to create a consumer-oriented and educational home for the Serenbe community, Imery drew inspiration from the basic reality of the real estate market. “If you don’t have a nice home with great curb appeal and that is designed well, then it’s never going to sell,” he says. Imery could either build a very efficient home without renewables or make a net-zero home. He decided to go for net zero so it would “have another mechanism to leverage what we are doing—which is consumer awareness,” he says. Although the house incorporates Passive House ideas, Imery says the design had to remain simple and stick to conventional techniques to prove to potential buyers that a net-zero home could indeed be built with traditional methods.

Siting and Shade

Imery and his team walked through the entire Serenbe community and finally zoomed in on a lakeside lot that faced a wooded area and was surrounded by a network of trails for easy access to anywhere within the community. A shade study was conducted to determine placement of shading devices, but reducing the window area in the west wall while encouraging high-efficiency design was difficult because of the lake views. To solve the problem, Imery used French doors that open up to an outdoor trellis and added shading devices to reduce heat gain.

Communal Water Treatment

The house uses structure plumbing, WaterSense fixtures, native landscaping with a minimal amount of sod, and sensor-controlled rain irrigation according to each plant’s requirements. Imery says the house would have had a water tank, but Serenbe uses a collective approach to capture all of its storm-water runoff to recharge underground water and also has a water biotreatment plant, so all wastewater is diverted to the system, filtered through the wetlands, and finally pumped back to each lot to be used for irrigation.

Dual Solar

Imery and his team wanted to build a home that had a projected HERS index of 45 before incorporating any renewables. The national average of an existing home has a HERS index of 130, but a new home built to code in Georgia would have a HERS index of 90. To achieve net zero in the Serenbe home, the home will need to generate 10 kilowatts per year. The roof features both photovoltaic and solar-thermal water heating panels.

Sealing the Envelope

The overall goal was to keep the shell as airtight and insulated as possible. To that end, the house features two-by-six framing, which increases the amount of insulation space and reduces the amount of lumber on the exterior wall when used with advanced framing techniques. One inch of rigid foam insulation was used between the exterior sheathing and wall to minimize cooling and heating loads. Imery also insulated the edge of the foundation with high-density fiberglass to reduce heat lost through the slab edge. And what especially is unique, Imery notes, is the use of a mini-split system to deliver heating and cooling into the home.