Net-zero home highlights builders’ growing interest in energy efficiency
- Sep 20, 2019 4:00 pm GMT
- 423 views
WRITTEN BYFrank Jossi
PHOTO BY Amaris Homes / Courtesy
Raymond Pruban's solar-powered home in Afton, Minnesota, stands out among a group showcased in the Twin Cities' Parade of Homes tour: The 3,000-square-foot house is expected to produce more energy than it consumes.
About two-thirds of homes on an annual Twin Cities tour now include a standardized energy consumption score.
The inclusion of a net-zero home on an annual Twin Cities home tour highlights the growing acceptance of energy efficiency in new home construction.
Raymond Pruban’s solar-powered rural rambler, located in a cornfield 20 miles east of St. Paul in Afton, Minnesota, is a rarity in that it’s expected to produce more energy than it consumes — even when accounting for the state’s cold winters.
The home’s performance was measured using a standardized index called the Home Energy Rating System (HERS), a tool that’s gaining mainstream acceptance among builders on the Parade of Homes tour. About two-thirds of the homes featured this fall have HERS scores.
“More and more consumers are starting to ask for the reports, and more builders see them as important to the sales process,” said David Siegel, executive director of the Builders Association of the Twin Cities, which puts on the Parade of Homes showcase.
Still, despite the growing attention to energy efficient building practices, greenhouse gas emissions from residential buildings are on the rise in Minnesota. In 2016, residential emissions were about 11% higher than they were in 2005, according to a January 2019 report to the Legislature.
HERS was created by the California-based Residential Energy Services Network and it has become, in many parts of the country, the de facto way the real estate industry measures residential energy efficiency. The Builders Association of the Twin Cities began using the method in 2012.
Builders hire independent raters who not only score their homes but work with them as consultants and suggest improvements, Siegel said. The association designates any HERS-rated house a “MN Green Path” home, regardless of its score, and issues a one-page home improvement report builders can share with clients.
Builders have an impetus to improve HERS scores because they can receive new home construction rebates for as much as $4,000 from utility conservation improvement programs. “It’s an incentive to be more efficient,” Siegel said.
Building Knowledge, Inc. owner Pat O’Malley, who does HERS ratings and worked on the Afton home, said the rebates more than pay for his services. Some measures required by HERS, such as a blower door test, have to be done to meet the state energy code.
HERS has done well in the Midwest. The Twin Cities has more than 20,000 HERS homes, and in Indiana and Iowa more than half of the new homes get rated. Indiana led the region with 9,781 rated homes in 2018, followed by Ohio, Minnesota, Iowa, Michigan, Illinois, Wisconsin and the Dakotas.
The Home Energy Rating System (HERS) Index is used to communicate the relative efficiency of a home to builders, developers and consumers. The scale is set with 100 being equal to the efficiency of a standard new home, and 0 being a home that produces as much energy as it consumes. (photo via Florida Solar Energy Center / Wikimedia Commons)
In Minnesota, new homes had an average HERS score of 51 in 2017, fourth best in the country. The leading states had only a few hundred homes rated compared to Minnesota, which generally sees more than 7,000 homes rated annually.
Many efficiency advocates credit Minnesota’s favorable HERS score to the state’s stringent building energy code. Siegel agreed but said the code also raises housing prices. The association wants to see builders given the option of following the energy code or meeting a minimum HERS rating.
Minnesota regulators are considering a change that would let builders reach a minimum HERS score of 61 (or 58 in northern half of the state) instead of complying with new code requirements. Homes would still need to meet standards from the earlier energy code.
“We would be fine with builders using HERS as long as there is the energy code backstop in place,” said Ben Rabe, director of built environment for Fresh Energy, a St. Paul clean energy advocacy organization and publisher of the Energy News Network.
Net-zero in a subzero climate
Pruban, owner Amaris Custom Homes, said attempting to construct a net-zero home in Minnesota’s harsh climate has proved frustrating. “I’ve tried to do this three or four times, and I failed,” he said. “It’s not easy to do this in a state with our winters.”
He has inched closer over the years, achieving a 9 HERS score on one suburban home before finally achieving net-zero with the Afton home on this fall’s Parade of Homes and another in a western Twin Cities suburb.
The 3,000-square-foot house showcased on the tour lists at $959,000. More than 40% of that was spent on land acquisition, landscaping and running gas and electric lines out to the rural property. Still, it is difficult to build an attractive net-zero home for less than $500,000, he said.
In Minnesota, net-zero homes require more insulation, high-efficiency heating and cooling, and a rooftop large enough to offset electricity use and any emissions caused by natural gas consumption for heating, he said.
Although electric heat pump technology designed for cold climates has significantly advanced, he was not confident it could keep the Afton home comfortable in the dead of winter. He opted to have both heating sources.
The house uses an air source heat pump for cooling in summer and for heating in spring and fall. A natural gas furnace will warm the home in winter.
Xcel Energy provides electricity and natural gas to the home, though much of the electricity will be produced from rooftop solar. The solar on the south facing garage roof produces 120% of the home’s electricity needs, creating enough excess power to cover the cost of natural gas.
A major challenge in a northern climate is having a rooftop large enough to fit enough solar panels to generate a home’s power needs, Pruban said. Even smaller homes will need significant roof space to get to net-zero. For the Afton home, he used a rooftop 20 feet wide and 40 feet long for the panels.
The Afton home had other features to help with efficiency. Walls are made of 13-inch think insulated concrete form construction. Smaller windows reduce heat loss. High efficiency appliances and LED lighting consume less electricity.
O’Malley worked with Pruban and believes net-zero homes will remain unique because higher cost of materials and equipment. “To be net-zero is tough,” he said. “But the things that matter we’re doing every day — improved windows, better insulation. It’s the stuff that’s not sexy. It’s not air source heat pumps or solar. But it reduces energy consumption.”
O’Malley works with Habitat for Humanity, which builds homes with HERS scores of 45 to 50 in the Twin Cities, much lower than most homes. Despite the higher cost of high-performance heating and cooling equipment, rebates and lower energy costs eventually pay for difference, he added.
Pruban likes to push the envelope of residential construction and his focus continues to be on net-zero. His expertise led to his inclusion in the Department of Energy’s Zero Energy Ready Home, a program that promotes and shares information about net-zero housing.
Most of the visitors who came the first week of the Parade of Homes showcase said they wanted to see what a net-zero home looked like.
Pruban is hoping one of them comes back and buys it. “A lot of people like what we do but can’t afford what we do,” he said. “But there’s still enough buyers out there that we’re always busy.”