What green|spaces is trying to do on the NorthShore might sound like magic. But Executive Director Michael Walton is no wizard. He and the others at the nonprofit simply want to prove it’s possible to build a home that consumes no net energy for a price that either matches what it would cost to build a house using traditional techniques or is negligibly higher.
The people at green|spaces are calling the project NextGen Homes, and their vision for it is as ambitious as their name for it suggests: they want nothing less than to spark a revolution in the local home building industry.
“Our mission at green|spaces is to advance sustainability in Chattanooga and the surrounding region,” Walton said. “Net zero homes are being built around the country but not in this market, even though a large percentage of the population appreciates our natural resources and wants to protect them so Chattanooga never again looks like it did in the early seventies. Green|spaces wants to prove there’s a viable business model for building these kinds of homes.”
Although examples of net zero homes exist, green|spaces took no short cuts on the path to designing its own development. Instead of adopting another project as a template, the nonprofit launched a competition that brought together several teams of architects, engineers, and builders to develop potential solutions. These home building professionals didn’t work in a vacuum, either, but factored in the wants and needs of active home buyers who took part in a focus group assembled to determine what people want in a NorthShore residence.
The initial design is based on the work of two finalists: Bema A/E, a local architectural and structural engineering firm, and a partnership between Vandemusser Design and SPARC Design in Asheville, N.C. Walton, an architect by trade, combined and modified the designs.
Designing the home in-house instead of basing the work on a similar project was vital to the success of the NextGen Homes venture, Walton says, because a net zero energy home must take advantage of its environment to minimize the need for mechanical heating and cooling. By being mindful of the local climate when designing each component of the NorthShore homes, green|spaces won a big part of the battle before it ever broke ground.
“Sustainability starts with what we call passive design,” Walton says. “We used to build buildings in a way that was responsive to their location. There was adobe construction in the southwest because the high thermal mass and small windows were perfectly adapted to the climate, whereas homes in South Carolina tended to have big porches and overhangs as a response to hot, humid southern afternoons. We moved away from that once we were able to mechanically heat and cool buildings.”
Green|spaces is building its NextGen homes on Hamilton Avenue, a narrow road cut into a steep hill visible from North Market Street. On this site, passive design involves southern facing glazing with overhangs that block sunlight in the summer, when the sun travels high across the sky, and lets in sunlight in the winter, when the sun travels lower on the horizon. This maximizes the benefits of the free heating and cooling the location provides.
Once an optimal passive design was in place, green|spaces tackled the envelope of the home. The goal was to make the walls, roof, and floors as air tight as possible to enable the occupants to heat and cool it using passive sunlight and natural ventilation. Unlike many aspects of building a house, this actually is as easily said as done.
“You can achieve a high performance envelope with almost any type of insulation,” Walton says. “To reach high levels of efficiency, you can combine a really good batt insulation with a continuous layer of rigid insulation on the outside of the building, or use blown-in cellulous or blown-in batt. Spray foam is also very tight.”
The final components of a net zero energy home are what Walton calls the mechanicals. Using passive design and maximizing the tightness of a home minimizes the need to heat and cool it extensively, Walton says; however, some heating and cooling will still be necessary. Plus, the creation of a tight envelope produces a need for mechanical ventilation.
To solve the ventilation problem, green|spaces is installing energy recovery ventilators, which will use the energy in exhausted air to pretreat incoming air. During the warmer seasons, the system will pre-cool and dehumidify; during the cooler seasons, it will pre-heat and humidify.
“In traditional homes, transom windows allowed cross breezes to travel through the building. It was a way of getting fresh air into every space,” Walton says. “An energy recovery ventilator is a modern way of doing the same thing, only we’ll be able to do it in every season, not just when we’re able to open a window. It’s an evolution of passive design that’s easy to do and not expensive.”
Each NextGen home will also come with a 4.75 kilowatt solar power system. While that might seem small, it’s all that will be necessary given the work green|spaces has done minimizing the loads on the interior of the building, Walton says.
As a bonus, the solar power system will be future-proof. Current solar storage technology is too expensive for many projects, but the cost will decline in three to five years, Walton says. At that time, NextGen homeowners will be able to connect their solar power unit to a storage system and take advantage of power purchase agreements and community solar arrangements.
“As the cost of efficient and renewable energy declines, we’re going to reach a point where it’s silly to build any other way,” Walton says. “We’ll arrive at that point within the next decade. As the price of electricity continues to rise, it makes more sense to generate your own.”
Finally, to heat and cool the NextGen homes, green|spaces will be installing ductless mini-splits from Mitsubishi. Mini-splits consist of a relatively small outdoor unit and insulated tubes routed through walls to multiple inside units. These systems typically supply air conditioned and heated air to a single room, although they can heat and cool up to a few rooms.
Walton says mini-splits are some of the most efficient systems on the market. “Most systems stop squeezing the heat out of outside air at about 40 degrees, but Mitsubishi can squeeze the heat out of temperatures in the single digits,” he says.
A major benefit of a ductless mini-split is the ability to customize how each room is heated or cooled. Setting each room individually allows the occupants of a home to minimize the need for electricity.
“Traditionally, you heat your whole home equally. But what if your lights worked the same way? What if you came home, flipped a switch, and all of your lights turned on?” Walton says. “Ductless mini-splits allow you to set each room at a different temperature. So when your 85-year old grandpa comes to stay with you and likes his room to be 88 degrees, he can be as warm as he wants to be and everyone else can breathe.”
In the past, net zero energy construction has been prohibitively more expensive than traditional construction. But Walton and his team considered the bottom line during each step of the design process, and were able to set an asking price for their homes close to what similarly sized traditional construction on the NorthShore costs: $350,000 for 1,700 square feet. Even better, the home was appraised for $360,000, which allowed green|spaces to finance the construction without any benefits for being a nonprofit.
“This project is intended to be replicable, so the cost had to be competitive with other construction,” Walton says. “And the price per square foot is similar to other projects on the NorthShore.”
There’s more good news for buyers, says Realtor Grace Frank, the listing agent on the NextGen homes: the return on investment will make even a slightly more expensive net zero energy home worth the extra cost. “The return on investment is fabulous. If you pay $10,000 more on a house, over the course of a few years, you’ll save that much if not more,” she says. “The value of a net zero energy home is typically ten percent higher than traditional construction, so we believe the resale value of these homes will be significantly higher than we’re pricing them.”
While 1,700 square feet would be a squeeze for a large family, it’s ideal for young professionals with a child or two and empty-nesters looking to downsize from a massive home on Lookout Mountain, Walton says. “Neither of those groups wants to spend their weekends tending a large yard,” he says. “They would rather walk to Frazier Avenue or a Lookouts games. Our small footprint is a direct response to the market.”
The market is the final piece of the NextGen Homes puzzle for green|spaces. Throughout the project, the nonprofit has trained architects, builders, Realtors, and appraisers, and the response has been positive. But to make sustainability the standard for home construction, the public has to begin asking for it.
“Builders aren’t building net zero energy homes because people aren’t asking for them, and people aren’t asking for them because they don’t know they can,” Walton says. “So we need people to want net zero energy homes, and to want them at a competitive price.”
The need to educate the public is one of the primary reasons green|spaces chose the site on which it is building the homes. Placing the houses on a hillside visible from a highly traveled street will hopefully spark curiosity and conversation, says Frank – a conversation she hopes leads to the stirrings of change.
“If more people become thoughtful about energy consumption and start pressuring builders to build energy efficient homes, then the market will begin to shift,” Frank says.
Green|spaces is aiming to complete construction on its first NextGen home in December. Once that residence is sold, the non-profit will sell and build three more. From there, green|spaces hopes builders will take the baton from them and run with the idea.
“We want builders to take the net zero concept all over Chattanooga,” says Frank, a board member of green|spaces. “In the past, green construction was a custom thing because the cost was prohibitively high. But we want it to become commonplace because it’s affordable and cost effective. Our goal is to see net zero energy homes become the standard housing concept in Chattanooga.”
Green|spaces is offering work-in-progress tours of its NextGen homes to Realtors, builders, and schools. For more information, call (423) 648-0963. To inquire about purchasing one of the homes, contact Frank at (423) 355-1538 or firstname.lastname@example.org.