In Search for Sustainable Materials, Developers Turn to Hemp

As ballroom dancers twirl, and competitive Ping-Pong players swing their paddles in the French town of Croissy-Beaubourg, they are doing so in what some describe as the future of building construction.

When the Pierre Chevet Sports Hallopened last year in the tiny municipality on the outskirts of Paris, it was the first commercial project in France constructed almost exclusively of hemp blocks. And many hemp enthusiasts predict this is just the beginning.

“It was the first time for everyone,”said Sonia Sifflet, lead architect on the project for Lemoal Lemoal, a boutique architecture firm in Paris. She said the sports center was a collaboration between the architects, material manufacturers, construction companies and town leaders. And now that they all know how to complete a hemp block project, Ms. Sifflet said, she expects to see many more in France.

“In five years, it will be normal to use hemp blocks,” she said. “There is no limit to what can be built.”

Interest in hemp as a viable substitute for construction material is growing as developers seek greener building options. Hemp can be used in block form, as it was in the building of the sports center, or poured like traditional concrete using hempcrete, a combination of lime, hemp fibers and a chemical binder. Hemp panels can also be used.

“There is a new focus on hemp in the United States; there is a tremendous opportunity,” said Petros Sideris, an assistant professor of civil and environmental engineering at Texas A&M University, which recently received a $3.74 million grant from the U.S. Department of Energy to research and develop 3-D printed hemp buildings. The entire supply chain is being studied, from growing hemp to using it in construction, he said.

The exposed hemp blocks require no special skills to assemble, reducing the amount of on-site construction staff needed.Credit…James Hill for The New York Times

Hemp is already used in a variety of industrial products, including rope, textiles and biofuel. But hemp construction is hampered by high costs and a supply chain that is not fully formed. And proponents must overcome resistance to a product that is often mistakenly tied to recreational drug use.

Advocates say hemp offers many environmental benefits that builders and policymakers seek when creating a carbon-neutral product that is also resistant to fire, mold and weather.

There are other benefits, Ms. Sifflet said. For instance, the hemp blocks require no special skills to assemble, reducing the number of workers needed on site. “They go together like Legos,” she said.

The simplicity allows for speed: A building constructed from ready-to-use hemp blocks can chop 20 to 30 percent off the typical production schedule, with no need for cement joints or the drying time required with traditional concrete blocks.

Hemp block construction allowed developers of the sports center in Croissy-Beaubourg to squeeze out every square inch to maximize space, Ms. Sifflet said. Using hemp blocks reduced the thickness of the walls, she said, because no insulation or finishing layers were needed, which freed up about 100 square feet for use.

And although using hemp blocks pushed the material costs 30 to 40 percent higher than traditional cinder blocks, the quicker production schedule allowed the firm to wrap up faster than usual, she continued, and the environmental gains offset some of the higher material costs.

“We did not do this because it is cheaper, but so it could be relevant and innovative in building public facilities with new material like hemp,” Ms. Sifflet said.

But hemp’s reputation as counterculture cannabis has been difficult to shake, slowing its acceptance in construction circles.

Rachel Berry is experimenting with growing hemp fibers on her windswept Illinois farm. As the founder of the Illinois Hemp Growers Association, she focuses on the plant itself and building out a viable supply chain from there.

“There are a lot of moving parts: growers, processors, manufacturers and companies using the hemp,” Ms. Berry said. But the first step is getting farmers interested, and hemp’s cannabis connection can cause them to tune out. “The stigma of cannabis still looms here,” she said.

The blocks reduced the thickness of the walls.Credit…James Hill for The New York Times
No insulation is needed, which freed up about 100 square feet.Credit…James Hill for The New York Times

Still, its recent approval for use in single and multifamily housing in the United States should increase hemp’s profile and pave the way for skyscrapers and warehouses to be made with hemp building materials.

That future is already taking shape elsewhere.

In Cape Town, the first such hemp skyscraper, called 84 Harrington, is already rising from the ground and, at 12 stories, will be the tallest structure in the world that incorporates largely hemp construction. Because of its load-bearing limitations, a traditional frame is still needed, but all of the walls are made from hemp blocks.

The building culminates decades of interest in hemp construction by its owner, Duncan Parker, a co-founder and the chief executive of Hemporium, a hemp producer in Cape Town. He said that the cost of building 84 Harrington was higher because hemp had to be imported from England, but that the first hemp cultivation licenses in South Africa were issued in 2022 and the first crops would be harvested next year, allowing for blocks to be made wholly in South Africa.

“We are building an industry,” he said, adding that it will take a couple of years for the supply issues to sort themselves out, but that once they do, hemp will be a construction staple.

The hemp skyscraper provided a fantastic hybrid between timber frame and masonry, said Wolf Wolf, the architect of the building. His firm, Wolf + Wolf Architects, is ready to move on a housing development with 25,000 homes made of hemp blocks.

“The critical mass is there now; we have crossed that threshold,” Mr. Wolf said, adding that his firm may have handled one or two hemp projects a year in past years but that now almost all major developers are asking for proposals incorporating hemp. “With climate change, people are taking it seriously,” he said.

The first hemp skyscraper, 84 Harrington in Cape Town, during construction last year.Credit…Sharne Bloem/Wolf + Wolf Architects
Because of its load-bearing limitations, a traditional frame is still needed.Credit…Sharne Bloem/Wolf + Wolf Architects
All of the walls are made from hemp blocks.Credit…Sharne Bloem/Wolf + Wolf Architects

In North America, others are looking to hemp as a potential panacea.

“Hemp is groundbreaking,” said Don Redden, chief executive of Ulmus Development, which is building a self-storage site made from hemp blocks in downtown Kelowna, a city of 130,000 people in British Columbia’s wine country.

Because of costs, home sizes in Canada have gradually been shrinking, which has driven up demand for storage spaces, Mr. Redden said. But a storage building is often viewed as a valueless blight, especially in an urban core.

“Usually a self-storage facility doesn’t look good, doesn’t add anything to the neighborhood,” he said. “So we wanted to build a building that would fit in.”

To help the five-story building become an asset in the neighborhood, it will include shared office spaces on the first floor. Mr. Redden said each hemp block would sequester about 13 pounds of carbon, which is more than what is expended in the making and shipping of the blocks. The building’s carbon equation tilts negative, he said, because it will actually draw carbon from the environment.

As hemp is catching on in other countries, builders, researchers and even hemp growers in the United States are studying its developments.

Multistory buildings still need a support system, but hempcrete can be used for the bulk of a building, said Mr. Sideris, the Texas A&M professor, who has material specialists, architects, structural engineers, material life span experts, faculty members and graduate students studying the best ways to use hemp in construction. He added that the demand for a sustainable building would rapidly propel hemp into other industrial and construction uses, and help make the material more economical to use.

“Once we have a clear demand, the market will self-regulate, and the price of hemp blocks and hempcrete will come down,” he said.

Advocates say hemp offers many environmental benefits that builders and policymakers seek when creating a carbon-neutral product that is also resistant to fire, mold and weather.Credit…James Hill for The New York Times

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