Mold-resistant and sustainable: ‘Hemp homes’ could be future of affordable housing in SC

JAMES ISLAND — As far as April Magill and Matt McQueen know, the building in their backyard is the first of its kind in South Carolina.

From the outside, it looks completely ordinary. It’s the size of a standard manufactured or mobile home, has a wooden frame and is slightly raised to protect the roots of a large tree nearby. But its walls are unique.

They’re getting handpacked with hempcrete and will be outfitted with sensors to track vapor movement, indoor air quality and energy efficiency once construction is complete. 

Hempcrete is a natural building material made by mixing hemp hurd — the woody part of the hemp stalk — with water and lime, which acts as a binder.

Magill, an architect and founder of the Rootdown Building Collective, has long been curious about its potential as an alternative to conventional insulation: Hempcrete is mold-resistant, antifungal, antimicrobial and fire-resistant. 

Conventional construction tries to seal water vapor out of walls. When water inevitably gets in, it gets trapped and creates the perfect conditions for mold. Hempcrete offers a solution. It lets water in and then breathes it out when humidity levels drop, Magill said.

Though hempcrete has been used in Europe and Canada for decades, it’s a relatively new building material in the U.S., only taking off after the 2018 Farm Bill legalized industrial hemp. Hempcrete is gaining popularity as a natural building material that handles humidity, promotes healthy indoor air quality, absorbs carbon and is energy efficient. Its benefits haven’t yet been thoroughly studied across climates, but some see its potential as a healthy, sustainable, affordable alternative to conventional construction materials.

Hempcrete’s ability to manage moisture and humidity is one of the main reasons people are drawn to it, but research and data that support these claims remain limited, Magill said.

This is where the building in Magill and McQueen’s backyard comes in. They plan to use it as a home office, but it’s main purpose is to test how hempcrete holds up in the Lowcountry’s coastal climate — and if it can be scaled and easily replicated for use in affordable housing construction.

“We’re not interested in super high-end custom hempcrete models,” Magill said. The building in the backyard is a stepping stone.

The Sustainability Institute — in partnership with Magill’s Rootdown Building Collective, the city of North Charleston, Riley Center and Community First Land Trust — is applying for a grant through the Environmental Protection Agency. The funding would cover building 13 affordable homes using hempcrete in North Charleston, Magill said.

“It’s a little bit of a precursor to work through some of the bugs so that if we get this grant, we can have a system ready to go,” she said.

Shrinking barriers

Tim Callahan, founder of Alembic Studio and Callahan Designs in Asheville, N.C., and Magill’s hempcrete consultant, has been studying hempcrete for more than a decade. He’s never seen mold grow inside of hempcrete.

“I have samples that I left out in the rain and just went through bad things,” he said. “I’ve occasionally sliced into (them), and they’re totally clean on the interior.”

Hempcrete is lightweight, absorbs carbon as it cures and can efficiently regulate temperature. The carbon emissions from producing hempcrete are substantially lower than what’s results from the production of other materials with the same insulation value, Callahan said.

People are increasingly curious about this new building material, and it’s gaining traction. Charleston County inspectors have shown support for the project, Magill said.

Hempcrete was approved as a residential building material in 2022 and added to the residential building code in 2024. This was a huge hurdle to overcome, Callahan said, but hempcrete still has a long way to go to become a mainstream building material — if it ever gets there.

“It’s not just a bunch of crazy hippies trying to do something with hemp, but that was the perception for a while,” Callahan said.

Growing industrialized hemp was legalized six years ago, when the 2018 Farm Bill removed the hemp plant and its seeds from the Drug Enforcement Administration’s controlled substances list. Before then, hemp hurd — one of the main ingredients for hempcrete — was hard to come by. It can still be difficult to source.

After the 2018 Farm Bill passed, most states adopted the federal regulations for growing industrial hemp. Other states like South Carolina opted for its own regulations, making it more difficult for farmers, said David Camby, a hemp farmer in North Carolina who provided the hemp hurd for Magill’s project.

If every state followed the federal regulations, industrial hemp could become a commodity crop, which would reduce the cost of hemp products, like hempcrete, Camby said.

As a specialty product, hempcrete is not cheaper to produce than conventional construction materials, but it’s comparable, Magill said. What hempcrete lacks in initial cost savings, it might make up for in long-term savings from lower utility bills and fewer maintenance costs from leaks, mold and rot, she said.

Magill hopes hempcrete will become readily available and affordable as interest grows and the federal government continues investing in “climate-smart housing strategies.”

“It just takes time when you’re dealing with these conventional systems that have been in the works for decades and decades,” she said. “It’s easy to feel defeated, like how can we ever compete? How could we ever make change?”

For Magill, change starts at the community level. The Rootdown Building Collective is hosting weekend workshops for people to learn about hempcrete — how to make it and pack it into the wall cavity.

Many of those attending the workshop want to build a home with hempcrete someday. 

“The DIY-nature definitely appeals to me,” said Spartanburg resident Kristi Hoffmaster, who attended the Oct. 5 workshop. 

Even though hempcrete offers many promising benefits, it’s not a magic bullet solution, Callahan. Rather, it’s a single component of a building that needs to interact with the entire system of building components.

“I often compare it to an orchestra where everything has a part to play, and they all have to integrate seamlessly for it to be a harmonious whole,” he said.

Nothing is perfect, he said. 

But hempcrete comes pretty close. 

“I don’t know of another building material that has performance characteristics that are as desirable as hempcrete,” Callahan said. 

Magill and Callahan are optimistic the hempcrete walls of the test building will hold up in the Lowcountry climate. If the data shows hempcrete can outperform conventional construction materials, that would be a bonus.