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Students designed a net-zero solar home in one of Colorado’s coldest mountain towns that could help a housing crisis

The challenge started on a lark during the Solar Decathlon hosted in Denver in 2017. University of Colorado students persisted with novice crew -- and through COVID-19 -- to build a sustainable option to the lack of affordable housing in resort communities.

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While touring a temporary neighborhood of student-designed solar houses in Denver a few years ago, college sophomores Gabi Abello and Hannah Blake wondered out loud: “This is so cool. We have to do this. Why doesn’t CU have a team?”

The two University of Colorado Boulder engineering students became the leaders of that team, which this week took the top award in the U.S. Department of Energy Solar Decathlon. The competition, comprised of 10 events (and CU ranked in the top three in all 10) attracts students from around the world who design and build a net-zero energy house. 

Gabriella “Gabi” Abello (on left) and Hannah Blake met as freshman roommates at the University of Colorado Boulder. They toured the Solar Decathlon showcase in Denver in 2017 and wondered out loud why wasn’t CU involved? Nearly four years later, they led the CU team to the top award in the 2021 Solar Decathlon build event. They designed a net-zero energy house in Fraser, Colorado. (Nathaniel Hottenstein, University of Colorado Boulder)

The novice crew from CU, a school that hadn’t competed since 2007, took on the additional challenge of building in one of the coldest towns in the nation (arguably, the nation’s icebox) and in a mountain community flanked by pricey Winter Park in one direction and Rocky Mountain National Park in the other.

But it was that fateful fall day in Denver that influenced the job. 

Kristen Taddonio and Joe Smyth, a Fraser couple touring the same Denver show house, overheard Abello and Blake’s conversation.

“We were at the time living in our very, very tiny apartment up here in Fraser and dreaming about, well, you know, the American Dream and having an actual house and a yard to call our own,” said Taddonio, who piped up after hearing the students discuss joining the next competition. “I handed Hannah and Gabi my card (and) said, ‘If you ever do put a team together and you need a client, get in touch.’ …And then I’ll be darned. The next year, they did call.”

Disrupted by COVID, the biennial event was supposed to take place in June in Washington, D.C. Everything went virtual with last week’s judging coinciding with the weekend before Earth Day. But a lot has changed since the first Decathlon in 2002. This round let participants choose whether to build locally or schlep the house to the national showcase, like the event Denver hosted in 2017. The CU team chose to build in Fraser.

Students from the University of Colorado Boulder were forced to change plans when the COVID pandemic hit. Instead of building the SPARC home in Boulder, they trucked the prefab wall panels to a lot in Fraser. The walls went up within two days and some members of the team spent another few weeks completing the build. (Jennifer Scheib, University of Colorado Boulder)

The CU team’s SPARC House is just under 1,200-square feet with 1.5 baths and a bedroom in the main house and a one bed/one bath in an accessory dwelling unit. It has solar panels, cold-climate heat pumps, a money-making rental unit and net-zero energy touches that keep the interior temperature steady, even when it’s minus 13 degrees outside. While the house is still on the electrical grid at night, excess solar energy captured during the day is sold back to the local power company, so overall, SPARC is net positive.

The location was a key to the Solar Decathlon win because unlike their collegiate competitors, Abello and Blake added the challenges of building the house in a rural mountain community known for its frigid temperatures, high housing prices and limited housing inventory. The median home price in Grand County was $740,000 in March, when more houses were sold than were newly listed, according to the Colorado Association of Realtors.

Addressing the housing affordability issue for workers in Colorado’s resort communities also became a compelling story. Ski resorts are close to home for Boulder students and the workers are often taken for granted, Abello said.

“We leave and we go back to our homes and we don’t really think about what happens in those towns,” Abello said. “After meeting Kristen and Joe, it gave us first-hand insight into people that live there full time, the struggles they face or their town faces, businesses that hurt because they can’t find people to support them and don’t have the means of housing and accommodating all of their workers.”

TODAY’S UNDERWRITER

The affordability equation

While affordability was important, the team felt the term was relative since affordable in the mountains does not mean the same thing elsewhere. They chose to make the home attainable — the A in SPARC — to give young, middle class couples a chance at home ownership in the mountains. (The acronym stands for sustainability, performance, attainability, resilience and community). 

“Our solution combines rental income with a portion of the house being a locked-off rental unit and the ability to grow into that space,” Blake said. “It’s flexible, there’s room for growth for the family, and also another really important part of that is that that rental unit provides living accommodation for seasonal workers who also have a lot of trouble living in mountain towns during the ski season or the offseason.”

To keep costs down, the team went with prefab construction. They found a generous partner in Simple Homes which let the students build prefab wall panels at the company’s factory in Denver. With the walls built, putting the home together took about two days — a process that is appealing in a town where the building season is short. It also cuts down on waste, said Jeff Hopfenbeck, co-founder and CEO of Simple Homes.

Students from the University of Colorado Boulder designed and built the insulated wall panels for their net-zero SPARC house in a Denver factory owned by Simple Homes, which specializes in using technology and off-site construction to improve efficiency and sustainability while limiting waste.(Jennifer Scheib, University of Colorado Boulder)

“We’ve done an apples-to-apples comparison and we use on average 10% less lumber than your average traditional on-site stick builts. Your average 2,000 square foot single-family house when built on-site generates about 5,000 pounds of waste during the framing process,” he said. “When lumber is at all-time record highs, this does have a meaningful impact in terms of cost in addition to the environmental benefits.”

Total construction costs for SPARC House, including the land, was about $440,000, Blake said, and “that’s definitely on the lower end of what’s currently being built.” 

Students from the University of Colorado Boulder were forced to change plans when the COVID pandemic hit. Instead of building the SPARC home in Boulder, they trucked the prefab wall panels to a lot in Fraser, Colorado. The walls went up within two days and some members of the team spent another few weeks completing the build. (Jennifer Scheib, University of Colorado Boulder)

When it comes to a net-zero piece, prospective owners need to also consider the “second price,” or the cost to operate and maintain the house. With 7.6 kilowatt solar arrays providing enough power to get the home to net zero, SPARC House’s energy costs are expected to be quite low. (The home is also battery-ready when the couple find a company that makes high-altitude batteries.) While a house cannot be considered net zero until after a year’s worth of tracking its energy use, data collected so far has the home producing more energy than it needs, Blake said.

Affordability and sustainability align with the Town of Fraser’s priorities. The town adopted sustainability initiatives in 2016 to reduce greenhouse gas emissions. It supports housing that uses less power — plus there are financial incentives and rebates offered by Mountain Parks Electric for energy-efficient appliances, electric-vehicle chargers and certain heat pumps, said Michael Brack, Fraser’s assistant town manager.

“It’s absolutely a big deal here because heating your home is the most expensive electrical cost up here,” Brack said. “Figuring out how you can solve that problem while keeping your utility bill under 240 bucks a month in the wintertime is a challenge and (CU) picked a great route with heat pumps and having those powered by solar.”

Inside the SPARC House in Fraser, the University of Colorado student-designed home has 360-degree views. Shown is the view from the second floor of the standing seamed metal roofing chosen for its durability. There’s also a glimpse of some of the 7.6 kilowatt solar arrays that provide energy for the home during the day with excess power feeding the grid. So far, the home is producing more energy than it uses. (Casey A. Cass for the University of Colorado)

Finding housing for workers in Fraser and other mountain communities has been an ongoing issue, said Brack, who estimates the split between year-round residents and second-home owners in the area is about 40-60. The town added a voluntary deed-restriction program last year that pays property owners who agree to have a full-time working resident always living on site. There’s only been a couple of takers. 

“Ask any business here in town and they’re typically understaffed. And, yeah, trying to find housing is the biggest challenge for people coming into this area, even for very well paying jobs,” Brack said. “If you’re trying to buy your own place here, it’s not easy. And the competition is high when something does come on the market that’s under $500,000.”

Taddonio and Smyth spent months searching for a house within their budget but found only apartments or older properties in need of costly repairs. 

“The other options were not really options for us,” Smyth said. “There’s a bunch of newer, very large homes that are literally millions of dollars. That’s part of the real estate market here. It’s pressure from much larger, often second homes, because it’s a ski resort.”

The SPARC House by the University of Colorado Boulder for the Solar Decathlon includes a rental unit to provide additional income for the homeowners to offset mortgage payment and flexibility to grow into the additional space. It also provide a place for renters who may be shut out of the resort area’s housing. (Nathaniel Hottenstein, University of Colorado Boulder)

So, the couple, who are in their 30s and have backgrounds working in energy and climate, bought a small plot of land in 2018 with plans to one day build their own home. Abello called them a month later or about a year after they first met. And that started everyone on the experience of a lifetime. 

“We came up with a list of must haves, which was very short. We wanted a simple roof that didn’t leak and a house that maximized passive solar heat gain, fit our lot and was within our budget,” Taddonio said. “For the students, it was, I hope, a really good experience of having a client that doesn’t have unlimited resources. You have to learn how to make compromises in the design and the process.”

Prefab, wool and cold climate heat pumps

Three years in the making, SPARC House started from scratch, with no current CU students or recent alumni around to offer advice from past Decathlons. Even the faculty adviser was new. Through connections, the team found Hopfenbeck at Simple Homes, a Denver company that uses technology and off-site construction to make building homes more efficient, sustainable and cost-effective.

Hopfenbeck, who earned his MBA at CU in 2016, heard through his network that CU students needed help. His company not only provided a factory space for students to work and build wall panels, but mentorship as Simple Homes staff guided them through 3D programs, tools and other technologies.

“Where I think the students really showed their skill was on the design side,” said Hopfenbeck. “They generated really fantastic 3D models that we helped coach and mentor them through. And, to me, the future of construction, the future of the homebuilding industry, really does come back to that data.”

Simple Homes’ standard panels aren’t insulated although the company does offer the feature. The CU team researched the best insulation for a colder climate. They picked sheep wool, using product from Havelock Wool for the interior and mineral wool insulation from a company called Rockwool on the exterior. 

The University of Colorado Boulder team researched the best insulation for a colder climate. They picked sheep wool, using product from Havelock Wool for the interior and mineral wool insulation from a company called Rockwool on the exterior. (Jennifer Scheib, University of Colorado Boulder)

“(Havelock) is a sustainable alternative to fiberglass,” Abello said. “It also maintains its (energy efficiency) value when it’s wet and has antimicrobial properties and is sound absorbing so it’s a higher quality insulation, but also so necessary in that region.”

By maximizing the home’s passive system — like wool-insulated wall panels and the orientation of the home — the active components, like the heating system, don’t have to work as hard, she said.   

A passive-certified home uses 40-60% less energy to keep indoor air quality conditioned compared to conventional buildings, according to the nonprofit Passive House Institute U.S.  The SPARC House did not pursue passive-house certification.

“There’s absolutely an increasing demand for passive-house certified homes, which is a philosophy around investing substantial resources in the envelope so that the house itself uses as little energy as possible,” Hopfenbeck said. “It allows you to then invest less in things like mechanical systems so you can sort of undersize mechanical systems because your envelope is so tight and so energy efficient.”

The University of Colorado Boulder SPARC House, which was the winning entry in the 2021 Solar Decathlon, has an electric induction stove from Beko appliances. Induction cooking compares more favorably to gas cooking than conventional electric stoves. Plus, the stove top stays cool on touch and only heats up when triggered by induction cookware. (Casey A. Cass, for the University of Colorado)

Other sponsors provided energy-efficient equipment. European appliance brand Beko donated the Energy Star kitchen equipment, including an induction electric stove. “People are enamored with gas ranges but we have been cooking now with induction and it is fantastic,” Taddonio said.

Mitsubishi Electric Trane provided its special cold climate heat pump, which operates like a reverse air conditioner by sucking the heat out of the cold outdoor air and sending it indoors (it’ll also turn into an air conditioner on hot summer days). It works perfectly at 5 degrees below zero, and has a 75% to 95% performance at minus 13 degrees and can still operate at colder temperatures, said Shawn LeMons, the company’s performance construction manager.

Because of the home’s design, the team used three small heat pumps instead of one larger unit. That was strategic because the house is three equal sized blocks. The two bottom blocks make a square footprint and sit on a site in shape of a parallelogram, with one side housing the rental unit. The third block sits on top of the main unit. By heating up individual spaces as needed, the heat pumps use less solar energy than a larger pump.

The University of Colorado Boulder SPARC House, which was the winning entry in the 2021 Solar Decathlon, has three cold climate heat pumps made by Mitsubishi Electric. The all-electric heat pumps work like a reverse air conditioner by taking heat from the outdoor air and pumping it indoors. The pumps work at 100% capacity down to negative five degrees. The colder it gets, the harder it is to heat up the house but at negative 13, the units operate at 75% to 95% performance. (Casey A. Cass, for the University of Colorado)

The cold-climate heat pump technology has been around for more than a decade but there wasn’t much U.S. demand even though the systems use 40% less energy than conventional ones, LeMons said. He said that’s likely because the U.S. was the first to commercialize residential air conditioning. Most homes aren’t replacing the technology. 

“Even now, the United States lags behind adoption of heat pumps (compared to) the rest of the world, where you’ll see 50 to 95%,” he said. “The United States is somewhere in the ballpark of 10% adoption.”

The University of Colorado Boulder SPARC House, which was the winning entry in the 2021 Solar Decathlon, uses cold climate heat pumps made by Mitsubishi Electric. The all-electric heat pumps work like a reverse air conditioner by taking heat from the outdoor air and pumping it indoors. A small unit is shown above the painting and is attached to a larger unit on the exterior of the home. (Casey A. Cass, for the University of Colorado)

Highlighting newer technologies and products is something the Solar Decathlon encourages. While many features are commercially available, student designs can turn into something bigger. 

The Ogden, Utah, house designed by Weber State University, for example, now has local developers hoping to include some of its features in their next homes, said Holly Carr, director of the Department. of Energy’s Solar Decathlon.

“My understanding is that those developers who reached out and have taken tours and want to look into this for their own development are mainstream,” Carr said. “They’re not the zero-energy developers. They are people who saw this and said, ‘What? $9 a month for my energy bills? Yes, please.’”

TOUR: Get a virtual tour of all nine houses built for the Solar Decathlon 

All of the student houses were built near the universities, which helped expose the community and local builders to sustainable products and design. Building houses locally will now be done for the next Solar Decathlon, Carr added. 

“This year more than any other we’re seeing that cross pollination with developers in the real world,” she said, adding, “many of these homes are already occupied with families.” 

Fraser couple Taddonio and Smyth finally moved into the CU’s SPARC House last week, after a few extra years of living in a 300-square foot apartment. By working with the students, they got their dream home within their budget. 

A photo taken on April 20, 2021 by the homeowners of the SPARC House in Fraser, Co. Kristen Taddonio and Joe Smyth moved into the student-designed house in mid April 2021. The nearly 1,200 square foot house produces more energy than it uses thanks to solar arrays on the roof, a heavily insulated envelope and ideal lot orientation. A chance meeting between Taddonio and Smyth and the University of Colorado Boulder students during the 2017 Solar Decathlon showcase in Denver proved to be the winning start. (Provided by Kristen Taddonio)

While land costs have since increased, the model could be adopted by larger developers who can reduce costs by building multiple houses. Potential owners could also adjust some of the expensive features the couple chose, including a metal roof for durability, smart appliances, and technology to manage when the house uses energy. 

“We’re excited about this house because it shows that we can build all electric homes in any climate. Fraser is one of the coldest spots in the United States,” Smyth said. “That’s one of the key solutions for addressing climate change, reducing air pollution from burning fossil fuels. You don’t need a gas connection for new homes.”

It’s only been a week but night-time temperatures have been in the 20s and so far, “it works great,” he said. “The house is at exactly the temperature you set it at and even when temperatures here — we’re still getting snow right now — drop well below freezing every night, the house stays perfectly warm and comfortable.” 


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