Kansas State University and Habitat for Humanity of the Northern Flint Hills are working on an affordable house in Ogden, Kansas, that will use hemp insulation to keep its residents warm in winter and cool in summer.
This is one feature that will help minimize the energy needs of the 864-square-foot home. A relatively small array of solar panels on its roof will then be able to power the household and even feed extra electricity into the power grid.
K-State architecture professor Michael Gibson said the low-energy home will help keep down electricity bills for whoever moves into it. And in just under two decades, the house will do something that a typical home never will — it will become carbon negative.
This means the Ogden home will finish offsetting the emissions that were generated by building it, and it will continue to churn out enough green energy not just for the people living there, but also for others.
Gibson, the faculty lead at K-State’s Net Positive Studio, said the project demonstrates the value of high-performance homes. And it shows that it’s time to take hemp seriously as an insulator.
“ I advocate for not thinking of this material as an exotic, weirdo material,” he said. “We could be using this to build houses right now.”
The federal government legalized hemp cultivation in 2018.
To K-State’s knowledge, the Ogden project is the first time in Kansas that permits have been issued for a house insulated with hemp. The project is also poised to become the first or second Habitat for Humanity hemp-insulated house in the country, Gibson said. (A Colorado affiliate of Habitat also has one in the works.)
The nearly finished two-bedroom, two-bathroom home in Ogden, near Manhattan, has hemp-based insulation in the floor, walls and roof.
The substance in the roof and walls looks somewhat similar to batts of fiberglass insulation. The one in the floor is called hempcrete.
Habitat for Humanity of the Northern Flint Hills, with grant funding from K-State, bought hemp grown on the Prairie Band Potawatomi Reservation north of Topeka, where the tribe’s agriculture business first planted the crop in 2020.
So far, Prairie Band Ag is seeing success growing it without irrigation or insecticide, and with minimal fertilizer. The tribe doesn’t till the field, which reduces topsoil loss. It plants winter cover crops to help the soil. When it’s time to make room for the next hemp crop, it uses a method called crimping to kill the winter cover crop with less herbicide than in typical farming.
“We’re trying to make our hemp and get it out into the world,” said Anthony Hale, a production hand at Prairie Band Ag. “Because it’s such a — how do you want to say? — a resilient plant.”
The goal is to develop business opportunities that benefit the environment and the Prairie Band Potawatomi Nation.
“It’s all tribally grown and tribally worked,” said John Melchior, lead operator at the company.
How the Ogden house reduces its carbon footprint
At Net Positive Studio, K-State architecture faculty and students work on affordable housing for urban and rural communities. The studio works with nonprofit developers and in areas with a need for quality affordable housing.
Habitat for Humanity of the Northern Flint Hills is the community developer and general contractor on the Ogden house designed by the Net Positive Studio.
The house is what architects call a passive building, meaning its features help the house use less energy. For example, the house will let in plenty of daylight so that the homeowners don’t need to turn on lights so much during the day. And its window placement will let the homeowners take advantage of natural ventilation to avoid running the heater or air conditioner on many days.
The hemp insulation is another key feature. Although very insulative, it doesn't insulate quite as well as foam does. Yet it makes up for that with a trait called thermal buffering that can help keep the house at comfortable temperatures.
Hempcrete excels at thermal buffering because the hurd gives it weight that resists the temperature fluctuations outdoors. The hempcrete floor will stay cooler than it otherwise would in the summer — and stay warmer in the winter.
Net Positive Studio designed the house with a raised floor specifically so that it could use hempcrete and reduce the use of concrete. A hempcrete floor doesn’t work well on the ground because it would absorb moisture from the earth below. So the Ogden house is raised on concrete piers, with a crawl space below the hemp-insulated floor.
The design lacks a concrete slab foundation. The house has only 15% as much concrete as would be normal for one of its size. And K-State makes the hempcrete alternative to concrete with very little energy.
This is an important detail because concrete production is a major source of carbon dioxide emissions.
Mixing hempcrete with local materials
The house will have a relatively small, affordable solar panel array on the roof. This keeps down the cost of the panels, Gibson said. It’s not necessary to install more solar panels because the house is so efficient that its residents don’t need so much electricity.
Gibson documents many details related to the house design and to making and working with hempcrete in a recent paper.
The material is straightforward to make, he said, meaning that contractors and community members can learn to mix it with local materials and wouldn’t have to rely on proprietary products or bringing in specialists from other states.
Gibson and students from K-State mixed hurd with water and a locally sourced binder, then let it harden and cure.
“You mix it up, sort of like baking or something,” he said. “That also made it fun to do with students because I think they kind of liked that part of the studio where we were mixing the hemp and moving it around and tamping it.”
The students tamped the hempcrete into the cavities of wood framing for floors. Later they moved the finished, dried panels from Manhattan to Ogden.
Students from Manhattan Area Technical College and the Home Builders Institute in Fort Riley also helped build the house.
A new option when others became more expensive
Hemp attracted Gibson’s interest during the COVID-19 pandemic, when supply chain problems made conventional insulation materials more scarce and expensive.
“At the same time there was a lot of expansion in industrial hemp growing in Kansas,” he said.
Hemp is a small but expanding crop in Kansas, where it is mostly grown for fiber and grain, rather than for producing CBD products.
Prairie Band Ag grows a hemp variety that has tall stalks and relatively few branches because the stalks are its goal.
The pithy inside of the stalks, called hurd or shive, can be chopped and put into hempcrete. The stringy outside, called bast, can be turned into the airy batts that look like fiberglass insulation.
Although building insulation is K-State’s main interest, that’s just one use that Prairie Band Ag sees for the crop.
“We have a lot of potential to make a lot of different products,” Melchior said.
The company mills the hurd into a variety of textures for different end buyers and is putting the material to work in new ways. This fall, for example, it test-produced its first batch of drinking straws and cutlery made entirely of milled hemp fiber and plant resin and now sells them in bulk.
Employees at the company said they’re excited to see industries find uses for the crop.
In the case of housing construction, Gibson shares that enthusiasm. Since hemp only became legal in the U.S. fairly recently, he said, it will take a while for the industry to adopt it more widely.
There’s a learning curve both for understanding what the material can do and for becoming comfortable with using it. For example, the proportion of water and binder in hempcrete needs to be correct for it to work as desired.
“And one kind of step in that process is just showing people,” he said. “It has an important purpose and this is how you use it and integrate it.”
Celia Llopis-Jepsen is the environment reporter for the Kansas News Service and host of the environmental podcast Up From Dust. You can follow her on Bluesky or email her at celia (at) kcur (dot) org.
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