Builders who use natural materials in the United States have seen interest grow in “hempcrete,” a renewable building material made with hemp that can take the place of traditional drywall, insulation and siding.
Since the 2018 Farm Bill legalized industrial hemp, the construction material — used for 30 years in Europe — has captured the imagination of American builders and homeowners.
“This year is the biggest year in hemp construction and it’s really just beginning,” said Tommy Gibbons of Ketchum, Idaho-based Hempitecture Inc.
Chipped hemp bark, lime binder and water are mixed together to make hempcrete. The material dries to a strong, stonelike substance that’s fireproof, mold-proof and insect-proof.
Walls can be constructed by crews without power tools who mix the ingredients together in buckets and pour them into wooden forms.
In Bellingham, Wash., homeowner Pamela Bosch worked with Hempitecture to build a 2,000-square-foot hempcrete addition to her 1898 Highland Hemp House that overlooks the San Juan Islands.
“It’s not a small experiment; it’s a legacy-size demonstration,” Bosch said.
She started her renovation looking for “natural insulation that didn’t have toxic fiberglass or foam,” she said. “I read about how hempcrete is used in Europe and never looked back.”
Hempcrete is a “carbon-negative” building material. The cellulose inside 2.5 acres of hemp can absorb more than 22 tons of atmospheric carbon dioxide, according to an Australian study. Hempcrete walls continue to sequester greenhouse gases as they cure.
The material is an antidote to the polluting construction industry, which belches out water and air pollution and fills landfills, said hempcrete pioneer Steve Allin, of Kerry, Ireland. Allin’s 2005 book, Building with Hemp, and his workshops in the United States have been the catalyst for hundreds of builders to try their own hempcrete projects.
Hempcrete takes the place of fiberglass insulation and sheet rock and can be covered with a lime plaster for smooth walls. It is not load-bearing like sand-and-gravel concrete, but can be built around a supporting timber frame.
The 9- to 12-inch-thick walls create an insulation envelope, keeping the house cool in summer and warm in winter. Walls also “breathe” with vapor permeability that keeps air inside fresh and prevents mold rot, according to European natural builder standards.
Homeowners should consider hempcrete for remodeling and repairs, Allin said. “Not all that many people get to build their own house. It’s not all about luxury homes.”
Hempcrete does not require expensive building equipment and can be applied by teams of relatively unskilled workers, he said. “Hempcrete can be built with community participation on a very local level.”
Not easy to obtain
But it’s not so easy to build a hempcrete house in the United States.
For one thing, hemp hurd, the plant material, is tough to acquire locally. Bosch and others have had to import hurd from Europe.
Farmers in this country have only just begun to grow hemp after it was formerly illegal in the United States for 80 years because of its relationship to its cousin, marijuana.
U.S. farmers appear more interested in growing the crop for CBD. That requires a short bushy plant, not the tall reed-like fiber variety. If farmers do grow the fiber plant, very few U.S. factories can process the crop.
“We need many processing facilities on the state level,” said civil engineer and hempcrete builder Sergiy “Doctor Hemphouse” Kovalenkov of Hempire USA in Los Angeles.
The secret to sustainability is working with local farmers who can grow hemp close to the site, Kovalenkov said, adding, “There’s no point in shipping hemp hurd from Poland when it could be grown locally.”
Kelly Thornton of Boulder, Colo.-based Left Hand Hemp said, “There should be millions of acres grown and processing facilities around the country like silos for the farmers to bring in their crops.”
The lack of hemp-processing facilities is the bottleneck unlocking the potential of hemp’s many uses, he said.
Another challenge for builders is that hempcrete has not been incorporated into building codes, said John Patterson, a 30-year expert carpenter in Fort Collins, Colo., who constructs “tiny hemp houses.”
U.S. hemp builders plan to form a trade association this year whose goal would be creating a path to include hempcrete in residential building codes. The group also would submit the material to U.S. Green Building Council, which grants LEED certification for sustainable buildings, Patterson said.
Other natural-materials building processes, such as strawbale construction, have paved the way for hempcrete in the International Code Council’s International Building Code.
Without proper certifications, it’s tough to acquire home insurance, building permits and construction professionals who will sign off on hempcrete projects.
“We are working our butts off trying to get architects and engineers and building officials to understand that hempcrete can meet or exceed the intent of the code,” Patterson said.
This year, some architects have taken notice of the material’s potential.
In June, students used hempcrete to insulate a small building on the Princeton University campus at the School of Architecture’s Embodied Computation Lab, Gibbons said.
“The material itself is exceptional, and it’s incredibly exciting that our students got to see it and apply it with a hands-on experience,” said Grey Wartinger, manager of digital fabrication, research and technologies at the lab.
Gibbons sees hempcrete as a way to build attainable homes for lower prices with hempcrete prefabricated walls, bricks, a spray application and even eventual 3D printing of hempcrete structures.
“We’ve seen the economics of this material, and how it can create jobs and build homes. We can help solve a lot of insecurity for people in my generation who can’t afford their own shelter,” Gibbons said.
Hempcrete is attracting homeowners who want a “rapidly renewable plant-based material that can change our manufacturing processes and move us away from oil,” homeowner Bosch said.
For hempcrete pioneer Allin, the big picture for hemp is its role in fighting climate change.
“We need solutions. We’ve spent the last 20 years telling people about climate change, and with hempcrete, we have this path to reduce our carbon in the construction industry,” he said.