NextGen Home rendering by WM Whitaker Landscape Architects

I joined the board of green|spaces this year. If you don’t know about green|spaces and the great work they’ve been doing for almost 10 years now, please head to www.greenspaceschattanooga.org to find out more. They are a nonprofit dedicated to advancing the sustainability of living, working, and building in the Chattanooga region.

One of green|spaces’ recent efforts to that end is building a group of homes called the NextGen Homes that will attain net zero energy use and putting them on the market for sale. Coming in at a reasonable $360,000, the NextGen houses are intended to demonstrate that smart, super energy-efficient housing is attainable right here and now in Chattanooga. To understand what a big deal this is, check out this article from the Wall Street Journal highlighting a model net zero house listing for $2.5 million and quoting builders who think net zero is not “commercially available” or “affordable.”

The first of four planned NextGen Homes is under construction now, and I’m pleased to be part of the team working to create, build, and sell this project. I look forward to deploying some of the smart building strategies we used here in future projects.

In order to get Net Zero Energy Certification (see here for info about the certifying body), a building has to generate as much energy as it consumes. To do this we design the house to use a minimum of energy and then design a solar array to meet or slightly exceed that energy usage. It may sound intimidating or hard to do, but the tactics we’re using here are common-sense approaches that can be used for any single-family home.

Siting and exposure. Of course we positioned the house to ensure year-round sun on the portion of the house that was going to get a solar array, but we also used the roof overhangs to provide summertime shade for the windows on the south side of the building. The east and west openings will be protected by deep porches or operable shutters.

Insulation and air-sealing. The insulation in the walls, floors, and ceilings of a house are what hold the heat or cold inside or out depending on the time of year. Fiberglass batts, the convenient and common solution, are not the most energy-efficient to begin with, and poor installation can reduce their effectiveness even further. So instead, we are using a Greenguard Certified spray-applied open-cell foam for the ceilings and crawlspace. The foam has a much higher insulation factor than batts, serves also as an air barrier, and helps with air sealing at joints and crevices. Of course no amount of insulation will help if the wind can blow right in around windows, doors, or electrical outlets. Which is why today we install some form of vapor-permeable air barrier. Like Gore-Tex for a house, the air barrier repels liquid water, allows water vapor to escape, and holds in the conditioned air. Air barriers take many forms—from building wraps to peel-and-stick sheets to rolled-on liquids— and the technology is always changing. The NextGen Home will use a self-adhered sheet with matching tapes to seal around windows and doors.

High-efficiency heat pump and energy recovery ventilator. Because when you seal everything up really tight, you actually do have to introduce fresh air through mechanical means. The benefit of doing this on purpose (rather than through a drafty window) is that the fresh air can be cooled or heated as it is introduced, and that reduces the load on the heating and cooling.

Solar array. The construction measures discussed above keep the house from using too much energy, but the other part of the equation is the 6 kW solar array, which will let the house generate enough renewable energy to meet its own needs.

Smart water use. Things like low-flow toilets and faucets reduce general water use. Pervious pavers on the patios and driveway let water through to the ground and keep it from running off into the streets and sewer system.

The house is currently under construction at 631 Hamilton Avenue on the North Shore, and should be completed by early summer. To see it in person, you can take one of green|spaces' regular tours as construction proceeds (info on tours here).

Project team:

green|spaces

Workshop : Architecture

WM Whitaker Landscape Architects

Collier Construction

Grace Frank Group

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