After 80 years of prohibition in the United States, industrial hemp is finally being recognized as a carbon-sequestering building material — one that has been used in Europe for more than 30 years.
Since the US 2018 Farm Bill legalized hemp, American natural builders are embracing hempcrete as new-yet-ancient building material that will revolutionize the construction industry. Some say hemp can create a built environment that can solve climate change.
The hemp plant locks up carbon as it grows, and can offset ecological damage from the construction industry, especially from the manufacture of mineral wool and fiberglass insulation, supporters say.
“Hempcrete,” or hemp+lime construction, is an insulating material that dries to a strong, stone-like substance that is fireproof, mold-proof and insect-proof.
The 9-12 inch walls on a hemp building form an all-natural thermal envelope, but even more importantly, the walls are vapor-permeable and naturally moderate temperature and humidity. A “breathable” outer wall solves water damage and mold issues and improves indoor air quality in buildings.
“People are getting switched on to how petrochemical-based building materials, like paints and plastic and finishes, off-gas and release harmful volatile organic compounds,” British hempcrete builder Alex Sparrow of UK Hempcrete said. He’s been building and retrofitting hemp-lime houses for a decade.
“Builders make housing more thermally efficient by making it air-tight and watertight, but then we end up trapping the toxins in with us.”Alex Sparrow
Sparrow’s early adopter clients in the “one-off bespoke house sector” are building their dream homes, he said. “But what we need to do now is step it up and start doing [hempcrete construction] at a much bigger scale.”
Hemp building technology is ancient, but also brand new.
Roman engineers used hempcrete mortar in 6th-Century bridges still standing in France. The material was rediscovered in the 1980s, when historic preservationists tried to repair the damage done on medieval lime-walled buildings that had been repaired with cement, which cracked and caused water damage to centuries-old wattle-and-daub walls.
Sparrow is one of many European hemp builders who’s been taking his expertise to builders in the United States, where a US Hemp Building Summit in Ketchum, Idaho, went virtual in 2020.
More than 300 people participated with an at-home kit to mix hemp, lime binder and water to make a solid 6” block.
Chopped-up woody inner stalk, called hemp hurd or shiv, smells of warm hay in the summertime. With gloved hands, participants mixed the plant matter into a lime-and-water mixture.
The sticky substance resembles the consistency of oatmeal cookie dough.
Two high school buddies in their 20s are the masterminds behind the US Hemp Building Summits, organized by Idaho-based Hempitecture, LLC.
New Jersey transplants Tommy Gibbons and Mattie Mead build custom homes from hempcrete. They sell a $7,900 imported French hemp blower that can wrap a home in a hemp insulation envelope in about three days. Hempitecture also imports and installs Canadian hemp insulation batts.
“We’re building with sustainable materials that are natural and healthier for the people who live in these buildings,” Gibbons said.
The construction method is simple: Moist, lime-covered hemp is layered and packed down between plywood forms, which are removed to reveal a thick fibrous wall that can later be covered with lime plaster or stucco. Sometimes it’s sprayed onto walls with the blower.
In 2018, the Hempitecture crew built the three-story Highland Hemp House in Bellingham, Wash., a 2,000 sq. foot solar-powered hempcrete retrofit of an 1898 home overlooking the San Juan Islands.
Homeowner and grandmother Pamela Bosch started the project looking for natural insulation that didn’t contain fiberglass or plastic foam.
“I read about how hempcrete is used in Europe and never looked back,” she said.
Her hempcrete home has an “old world” feel, with thick plaster walls that retain heat in the winter and create “great acoustics,” Bosch said.
Gone are the black mold and carpenter ants that plagued her former home.
It should stand for another 100 years.
But more importantly, Bosch believes the house is a testament to reimagining construction completely.
Hemp building is a “disruptive” technology that will help save the Earth, says Pamela Bosch, designer and owner of the Highland Hemp House in Bellingham, Wash. Photo courtesy of Pamela Bosch
“Using hemp for building materials is one of those disruptive strategies that would have a net positive result on humanity, on culture, on the environment of Earth,” Bosch said in an email. “I get impatient because logically, shifting from oil consumption to carbon capturing materials is critical to human thriving (if not survival).”
Bosch said she prevailed against contractors who considered her an “easy mark” because of her age, and she’s proud her home embodies the democratizing qualities of hemp construction.
“If a grandmother can make this house, anyone can,” Bosch said.
Other US builders take a more practical view.
“Hempcrete is just a superior insulation material,” said Virginia developer Ray Kaderli, of Triple P Fund, who is building rental housing with hempcrete insulation in San Antonio, Texas.
“Most hempcrete homes right now are magnificent wonders,” he said. “My plan is to build 100 homes over the next five years that are not magnificent. To me it will be exciting to make hempcrete boring and commonplace.”
Kaderli will be importing hemp hurd and binder from Europe this summer.
“Most builders will not go to France for a product to build locally. I am, because I know I can do it stateside in the future,” he said. “I know in Texas there are large fields where hemp can be grown and on the other side of the highway there is a lime quarry.”
Construction Waste and the Climate Damage of Insulation
Insulation is not a sexy building material, like high-end finishes or luxury appliances.
But insulation is one of the most polluting products used in home construction, according to the U.S. Environmental Protection Agency. The manufacture of mineral wool and fiberglass contributes more than 30 percent of the stratospheric ozone depletion from the “pre-construction phase” of single-family homes.
What does that mean to people who live close to where insulation is manufactured?
Insulation must be fireproof, so companies like Danish-owned Rockwool create their products by heating basalt and other minerals to 2,700°F and spinning out fiber strands which are carded into insulation batts.
In Ranson, W.V., Rockwool plans to open a 460,000 sq. foot mega-facility near historic Harpers Ferry and the borders of Pennsylvania and Virginia, causing alarm to the local residents. The factory will burn 650 tons of rock a day, as well as recycled mineral wool and slag from the steel industry. Tens of millions of dollars of state incentives have been coughed up for the project.
Jefferson County Vision, a citizen group opposing the factory, believes the factory will turn their valley into an industrial hellscape.
“The future of this valley really depends on this fight,” Tim Ross, of Jefferson County Vision, said, “And we could beat them if our state was not actively working against us.”
“The facility will sit about 2,300 feet from North Jefferson Elementary, a Title 1 school, on land bordering an African American cemetery in the poorest district in the state,” Ross said.
Air permit documents show plans for two 213-foot high smokestacks emitting 239 tons of Nitrogen Dioxides (NOx’s) and 472 tons of volatile organic compounds (VOCs) per year.
Rockwool says the company’s recycling keeps waste material from landfills. The company says it will provide up to 150 jobs, and insulation produced in a single year will save 1 billion metric tonnes of CO2 over the lifetime of its use (about 50 years).
But those benefits won’t much help people who live nearby, Ross said.
Air-inversion patterns in the valley will make the pollution linger, Ross, a retired federal weather scientist, predicted. Residents fear cancer-causing chemicals such as benzene will end up in groundwater which flows through interconnected caverns of karst limestone.
Rockwool‘s West Virginia spokesman, Paul Espinosa, Republican majority whip for the state house of delegates, did not respond to an interview request.
Meanwhile, construction and demolition debris accounts for half of the solid waste generated every year worldwide. Construction waste is predicted to double in the eight years between 2017-2025.
Hempcrete builders compare this to an acre of industrial hemp that can sequester 60 tons of carbon in only three to four months of growing, and continues to absorb CO2 in hempcrete as it cures.
“It’s a natural product, sustainable, easy to grow,” UK Hempcrete’s Sparrow points out.
Some of hempcrete’s biggest supporters are professors at New York’s Parson School of Design’s Healthy Materials Lab. For five years, the lab has been researching hemp-lime construction, and even released a new free 200-page book this year that looks at the large hemp-lime projects that have been built in Europe and around the world.
Now they are trying to bring a “knowledge transfer” of hemp-lime construction as a way to create healthier shelter in the United States, especially in low-income housing, said Alison Mears, architect and director of the lab.
“When we’re looking at affordable housing, the residents are often exposed to the worst products in the marketplace,” Mears said.
In pre-pandemic 2020, Parsons students and architecture professors traveled to Newcastle, a rustbelt town in western Pennsylvania, to build and learn how to design with hempcrete.
They teamed up with DONS Services, a disability advocacy group, which restores blight housing. DONS received a $75,000 grant from the state agriculture department to restore a 1,000-square foot home with hempcrete to make a demonstration building called the “PA Hemp Home.”
Even though Pennsylvania farmers got into growing hemp late in the game after the passage of the 2018 Farm Bill, “most people don’t know there is a pocket of hemp activity in Pennsylvania,” Lori Daytner of DONS said. “There’s not a lot of economic opportunity here. Most industries left a long time ago.”
But Pennsylvania is betting on hemp.
Taking a model from the farm-to-table movement in restaurants, Coexist Build, a hemp construction business in Maiden Creek Township near Reading, Penn., is focusing on localized supply chains. The company casts 8 x 16 x 6-inch pre-cured hempcrete bricks.
“We can grow the hemp here, we can make the binder, we can make the blocks here,” said Architect Ana Konopitskaya. “We are working hard to bring that local economy to Pennsylvania, with a completely in-state supply chain and distribution line.”
The bricks can be used for facades or interior walls with a thin lime mortar. The company also makes an insulation blanket out of hemp fiber. Coexist remodeled a stone vintage building as a hempcrete guesthouse and built a traveling mini hemp house on wheels.
The idea is to reproduce local supply chains regionally, said the late hemp advocate Dion Markgraaff of the Denver-based US Hemp Building Association, in an interview before his death in February.
“Farmers can grow hemp locally. Lime is everywhere, water’s everywhere,” Markgraaff said.
In the United States, the supply-chain bottleneck is processing hemp from the fields, using a process called decortication, which separates the outer fibrous bark, or bast, from the hurd.
In Europe, hemp fiber processing factories have pushed the hemp construction industry forward.
But the sole U.S. hemp processing factory, Louisville, Ky.-based Sunstrand, filed for bankruptcy in January, 2020, after being unable to acquire enough raw materials to process.
New processing facilities cost up to $30 million and need to be regional to make hemp a competitive crop to grow. Meanwhile, builders are importing hemp from Canada, where it has been legal since the 1990s, and Europe.
But hemp production screeched to a halt with the federal clampdown that followed the passage of the Marihuana Tax Act in 1937, which outlawed THC cannabis but also swept non-psychoactive hemp into a state of prohibition.
Hemp growing and processing was building up steam in the United States in the early 20th Century, when dozens of steam-driven processing mills, mostly in Wisconsin, employed hundreds of workers.
Hemp was touted as a “new billion dollar crop” in a 1938 “Popular Mechanics” article, with the plant’s 77% cellulose hurd that could be ”used to produce more than 25,000 products, ranging from dynamite to Cellophane.” In 1941, Henry Ford made a car body from hemp plastics that was impervious to the sledgehammer.
“Imagine what would have happened if we would have subsidized this technology 100 years ago instead of oil and gas,” said Morris Beegle, co-founder of Colorado Hemp Company and producer of the Let’s Talk Hemp podcast.
“There’s hemp and kenaf and flax and all kinds of fibrous plants out there that could be made into bio-based plastics and other materials.
“Let’s not extract it from the ground. Let’s move from hydrocarbons to carbohydrates,” Beegle added. “Let’s make the transition to a plant-based economy to replace a petroleum based economy. It’s a win-win for the United States.”
As the American West confronts the realities of climate change, and raging historic wildfires, hempcrete’s fireproof qualities are the answer for builders, the late Markgraaff of the hemp building association told The News Station at the end of last year.
“You should get better insurance rates if you build with hempcrete,” Markgraaff said. “In fact, it should be illegal not to build with hempcrete, because it’s so overwhelmingly positive.”
Markgraaff, 51, led regular hempcrete building workshops in Vista, Calif.
Markgraaff, known for his fierce advocacy for cannabis and hemp building, said he saw parallels with the coronavirus pandemic and climate change. “Climate change is like a virus on the earth — and hempcrete is like the vaccination we’ve all been waiting for,” he said.