The local architectural firm Antidote is designing net zero homes for North Chattanooga that produce at least as much energy as they consume.

Green|Spaces NextGen homes

* About: The four homes will produce as much energy as they consume and use building materials that don’t damage health. The International Living Future Institute grants net-zero certification.

Location: 631 Hamilton Ave., North Chattanooga

* Construction: Begins on first home this spring and will take six months

* Size: 1,700 square feet, 3 bedrooms, 2 1/2 baths

* Projected sales price: $350,000

* Features: Solar panels, potable water conservation, natural stormwater management materials sourced regionally that are sustainable and durable, smart ventilation with an energy recovery ventilator

Source: GreenSpaces

There's a house in Chattanooga that produces at least as much energy as it uses, a first for the city. Another is on the way, with several more planned.

You could say it's part of a green-building trend – although net-zero homes, as these homes are called, take sustainability a step further.

It's not all about being kind to the earth, though idealists might like to think so; instead, cutting utility and other costs is a big motivation, according to local architects and a recent survey by the U.S. Green Building Council.

For example, a local firm, Antidote, designed a 2,200-square-foot home in North Chattanooga for a family wanting to keep bills low for their son, who would be living in it. Construction on the $319,000 home finished in March 2015. Antidote is seeking net-zero certification for it (it takes a year to collect the data to qualify through the International Living Future Institute).

Meanwhile, this spring, GreenSpaces expects to start construction in North Chattanooga on what it hopes will qualify as a net-zero home. The $350,000 home should be done by the end of the year and is on the market, with three more planned on the site at 631 Hamilton Ave.

GreenSpaces's NextGen homes, as they're known, are the result of a design competition that the nonprofit organization sponsored in 2014 to help regional architects, engineers and contractors develop workable market-rate solutions for net-zero energy homes.

GreenSpaces had anticipated completing the project last year, but after working with the winning team, couldn't bring the price under $420,000.

"There's kind of a cliff at $400,000," says Michael Walton, executive director for GreenSpaces.

So, it reduced the size from about 2,200 square feet to 1,700. The home still has three bedrooms and two-and-a-half bathrooms. The site's steep grade makes it challenging for construction, says Walton, an architect.

GreenSpaces consulted with the team that placed second in the design competition, Sure Foot Builders in Asheville, North Carolina, where steep slopes and green homes are frequently found together, Walton says. Then, GreenSpaces designed the home in-house with help from Workshop Architecture and Collier Construction. Landscape architect Matt Whitaker designed the low impact and low-maintenance landscape, and SK Collaborative helped with energy modeling.

Losing the original design wasn't a total loss, Walton says. Indeed, the final design was informed by it. And the competition was about raising awareness for net-zero energy construction, not just about a final product, he says.

"I wouldn't necessarily have done something differently," Walton says. "It was as much about the process as the end result."

During, and even after, construction is done, GreenSpaces will offer tours of the home.

Antidote is also trying to shine a light on sustainable construction, through its new program, Antidote Living.

That's why it's building three spec homes in North Chattanooga with nationally sourced materials that aren't toxic. One, located on Oliver Street, is expected to be a net-zero home. The homes range from 2,200 to 2,400 square feet and are expected to cost $439,000 to $450,000.

"If you don't make it available, people aren't going to buy into it," says Antidote co-owner Tyler Smith.

A report released in February by the U.S. Green Building Council showed that green building doubles every three years. Conducted in nearly 70 countries, the Dodge Data & Analytics World Green Building Trends 2016 SmartMarket Report found that economics were the driving force behind the trend – namely saving money through lower operating costs. This applied to emerging economies, such as Brazil and India, too, the report said.

GreenSpaces says its NextGen homes will be free of urea-formaldehyde and VOCs (volatile organic compounds), and deliver filtered fresh air to every room. Low-impact landscaping will preserve trees and incorporate low-maintenance native plants.

There will be parking (with pervious pavers) for two cars, but residents will be able to walking to grocery stores and other shops. They'll also be near Bike Chattanooga stations, bus stops and the electric shuttle.

"Residents (can) live car-free if they please and use the parking area as an additional patio," Walton says.