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Solar Decathlon Technology Innovation Blog Series: Building Enclosures

Thursday, December 3, 2020

This is the first in a monthly series on Solar Decathlon Build Challenge technology innovations, through which we will explore innovative technologies and strategies 2020 Build Challenge teams are employing in their houses. This month’s post focuses on building enclosures – or walls, windows, roof of the homes. Stay tuned for posts on indoor comfort, energy performance, water efficiency, and much more!

Since 2002, the Solar Decathlon has invited collegiate teams to design and build highly efficient and innovative buildings powered by renewable energy. As we ramp up to the Solar Decathlon Competition in April 2021, the new Solar Decathlon Tech Innovation blog series will highlight innovative products and strategies teams are employing in their homes to achieve competition goals. This edition focuses on building enclosures. We caught up with representatives from three Solar Decathlon student teams learn more about their unique approaches to walls, windows and roofs.

Kansas State University’s Net Positive Studio is a multiyear effort in which students pursuing a master’s in architecture work with local groups in Kansas City’s Historic Northeast neighborhood. The Kansas State team is developing a high quality energy-efficient home that is affordable for low-income households.

The Warrior Home team designed by the University of Waterloo team in Ontario, Canada, has completed a four-bedroom, single-family home to address the cultural and societal needs of families within the Chippewas of Nawash indigenous community in southwest Ontario.

The CampusCraft team at the University of Denver has undertaken the net-zero renovation of a single-family residence located in the Denver floodplain. CampusCraft has developed a cost-effective plan following Federal Emergency Management Agency (FEMA) guidelines to update a 1950s home with energy-efficient technologies.

What is your home’s enclosure technology or strategy, and why did it make sense for this house?

The Kansas State team went prefab, putting components together in their facility on-campus in Manhattan, Kansas, then moving them to the building site in Kansas City.

“Inside our panels, we have conventional wood-stick framing,” said Michael Gibson, an associate professor at Kansas State. “But I think the main difference is we’re using a polyurethane-based structural insulated panel (SIP) from Raycore. Their panels have foam with 2-by framing within the panel. And so we use that as our load-bearing structure—our walls—and then we put oriented strand board (OS) on the outside of that, and then continuous insulation on the outside of that. And then we use Huber’s ZIP System® on the outside as our weather barrier and an air barrier system.”


to people installing the structural insulated panel (SIP) from Raycore.

Gibson said the team’s roof design was also prefabricated, which improves the energy efficiency of the whole building. “You want the roof and the ceiling systems to be just as high-performance as the walls,” he said. So, his student team built four-foot-wide roof panels with framing in between as a secondary system.

Gibson said the team’s roof design was also prefabricated, which improves the energy efficiency of the whole building. “You want the roof and the ceiling systems to be just as high-performance as the walls,” he said. So, his student team built four-foot-wide roof panels with framing in between as a secondary system.

The University of Waterloo team faced the challenge of building an affordable home in a new housing development, working with Habitat for Humanity. “The exterior above-grade wall assembly consists of vinyl siding secured to 1×3-inch furring strips, spaced at 24 inches on-center, with four inches or R16 of expanded polystyrene insulation on the exterior,” said undergraduate research assistant Shuxian Nian. “We chose to use OSB with taped joints as the air barrier since Tyvek® can be prone to tears. Interior insulation between the studs consists of 5.5 inches of R20 of fiberglass batt insulation, followed by an interior gypsum board finish.” Nian said the ventilated roof assembly makes use of a raised-heel truss, which “minimizes thermal bridging at the exterior wall-to-roof interface by allowing for increased insulation around the perimeter of the roof. The thermal performance of the roof assembly comes from 17-inch or R63 of loose fill cellulose insulation, with proper use of a vent baffle to ensure the insulation remains as installed. A six-millimeter poly sheet mechanically fastened to the ceiling joists acts as the air barrier.” R-value is a material’s resistance to conductive heat flow. The higher the R-value, the more the insulating effectiveness. Typical recommended R-value for homes in northern U.S. climate zones and Ontario is between R-50 and R-60.

The University of Denver team challenge was unique: Their team is retrofitting a 1956 ranch house with two levels of 1,050 square feet each. “Our existing enclosure system is a two-by-four exterior wall with a three-quarter-inch drywall plaster system on the inside,” said Eric Holt, an assistant professor and 2011 Solar Decathlete (his team at Purdue University placed second). “There [was] zero insulation in the walls, so we had a company called Rocky Mountain RetroFoam come in with a drill-and-fill latex foam system that expands and fills up the cavities.”


a man conducting a drill-and-fill latex foam system instillation

What are the benefits of this tech over the more common or traditional technologies?

Kansas State’s Gibson pointed to the relative simplicity of putting together prefab components in the field. “In conventional stick-framing construction, there are all these details and intersections that happen between walls and roof, and roof and ceiling, which can actually be very troublesome,” he said. “And architects can’t really draw those to a high degree of detail, because a lot of that stuff is dependent on the skill of the contractor in the field, and how insulation and the parts of the building are actually applied and fit together. In our case, we were able to really control a specific joint in the system and develop that detail at the beginning of the design process. So the students understand how the pieces fit together really clearly. And watching it come together in the field, it’s a lot more controlled.”

Simplicity in design and building techniques was key to the University of Waterloo team because of its work with Habitat for Humanity, which uses volunteers for many phases of construction. “As such, the design must be simple enough for volunteers with little to no construction experience to assemble, and not require a specialist to install,” said Nian. “Or, if a specialist is required, this labor must be kept to a minimum.”

The University of Denver team marveled at the difference in energy efficiency made by a drill-and-fill product. “The beauty of RetroFoam is that it’s super, super clean,” said Holt. “Because the foam does have some expanding properties, it really starts to fill that cavity fully, and air seal things up. Those are a lot of the reasons that we chose to go with it. We’re retrofitting an existing plan, so what would a typical homeowner do? What are their options available that are highly cost-effective, feasible, and realistic? This checked all those boxes.”

Does it cost more than the traditional methods? If so, how did you justify the additional cost? What made it worthwhile?

In going for maximum energy efficiency, the Kansas State team was willing to accept some higher front-end costs, knowing there would be tremendous savings on energy bills down the line. “I think everything we’re using probably costs a bit more… [but] we’re only talking about maybe a $5,000 or $10,000 difference in overall construction cost,” said Gibson. “Having those Raycore blanks really speeds up the process because our on-center framing is already there for us. It’s really just a matter of cutting the Raycore and then fitting in all the perimeter pieces and nailing everything together. And I think it also adds another level of durability to the panels when we’re shipping and handling them on-site. And I’m not even getting into the energy savings.”

Opting for a basic, traditional building enclosure that could be executed by volunteers maximized cost savings for the University of Waterloo team. “The cost to construct the building enclosure was not significantly higher than traditional homes constructed in the area,” said Nian.

Are there any new skills or tools needed to use or install the products?

The Kansas State team, all architecture students, had taken great pride in their construction and fabrication drawings, but due to the prefab concept, “We have our drawing sets out in the field just kind of getting dirt on them,” said Gibson. “Working with prefab, there really is just one way that the building goes together.”

The University of Waterloo team kept it simple because of the involvement of volunteers down the line. However, said Nian, “To guide the volunteers, we have put together a constructability manual that will go through step by step how to install and construct the various assemblies of the home.”

Where can homeowners or homebuilders find these products and/or get more information?

Retrofoam is available from dealers nationwide. “It’s super eco-friendly, with very good insulation value, especially when you start from zero in the walls,” says University of Denver’s Holt.

The University of Waterloo Warrior Home enclosure and the nature of the entire project inspired a different, nontechnical answer from Nian: “What’s unique about our project is that by partnering with Habitat for Humanity as our builder, our house will not go on the market. Instead, it has been assigned to a deserving family and sold at a low cost through the Habitat process. To apply for this opportunity, families must agree to be a ‘partner family,’ which requires multiple qualifications: the family must be willing to spread the word about Habitat for Humanity, volunteer 500 hours of sweat equity toward building their home or volunteering at their ReStore, and be willing to learn about home ownership responsibilities.” More information about homeownership and volunteer opportunities with Habitat for Humanity is available at their website.



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