Park City, Utah, is famous for its snow, a fine powder that lands on the mountain and stays for months. In 2023 that snow was destroying a development of luxury ski condos. The buildings had begun to rot through the long winters, and David Fine, the builder hired to renovate them, took on a problem the homeowners’ association had already spent a year trying to solve.
The requirements sounded modest and turned out to be hard. The cladding had to cope with moisture. It also had to resist the wildfires that threaten the mountaintop in summer, and those fires now come more often. Extruded aluminium would hold back flames, but it would look synthetic. Cedar would look right, but its fire rating was weaker. One option was safe and ugly, the other attractive and flammable, so the association kept looking.
The answer came from the rice paddy. As Nick Aspinwall reports for BBC Future, the condos were clad in panel boards made from rice husks. “Their focus was to find something that looked like wood, that was beautiful, and that was a little better fire-rated than traditional wood siding,” Fine said. The husk panels, in his words, “checked all those boxes”.
What the field throws away
While the plant is growing, the husk protects the grain from moisture and pests. After the harvest it becomes one of the most stubborn wastes in farming. In the United States, rice producers have left it to decompose in the ground, where it gives off methane, a potent greenhouse gas.
That waste caught the attention of Christopher Guimond when he was an engineering student. He became convinced the husk could be used at scale in construction. “The fascination was to take this thing that was a throwaway and leverage its properties,” he said. He is now chief executive of Modern Mill, founded in 2018 and the first US company to make construction products from rice husks at scale. The company says it has kept more than nine million kg (20.5 million lb) of husks out of landfill, including the husks in the Park City panels. Its board, sold as ACRE, is made from husks blended with polymers. According to the Mississippi Business Journal, the husks come from mills in the Mississippi Delta and are ground, compounded and extruded in Pike County. The company describes its plant in McComb as a zero-waste facility.
The reasoning is as old as the crop. The husk is rich in silica, which helps it resist damp and decay, the same qualities builders look for in conventional materials. “The whole point of the rice husk is to protect the rice while it grows,” Guimond said. “What is it protecting it from? Moisture, pests, rot, those types of things.” Fine says the silica also makes the material surprisingly resistant to fire. Modern Mill’s panels are designated Wildland Urban Interface (WUI) compliant, which means they have passed California’s fire safety tests.
One reflection seems fair. Something a farm in the Delta paid to get rid of now protects luxury homes in the Rockies. The value of a thing depends partly on who decides to pick it up.
The ledger of carbon
Timber has long had a reputation as the sustainable choice. It is plentiful in continental climates and produces relatively low emissions compared with concrete and steel. Crop residues may offer more. A University of East London study published in January in Cleaner Environmental Systems found that fibrous leftovers from rice, wheat and maize could lock away carbon for decades if they went into insulation, boards and panels instead of being burned. Those three crops produce 3.3 billion metric tonnes of residue a year worldwide, most of it burned for energy, according to Anthropocene magazine.
Sabbie Miller, a professor of civil and environmental engineering at the University of California, Davis, who studies sustainable building materials, warns against easy conclusions. Whether a given material is actually low-carbon is a complicated question, she says, and answering it takes a detailed life cycle assessment.
In Italy, the company Ricehouse used rice as insulation in a house designed to replace an earlier building. Its large south-facing windows and open kitchen let in sunlight and air, but also seasonal heat and echoes. “We had to add another way to insulate more and guarantee acoustic comfort,” said Valentina Savioli, the company’s communications officer. Choosing rice was easy, she said, “just because of how much volume and biomass [it] has”. She added that Italian contractors are generally sceptical of unfamiliar materials, and that could slow wider use.
The fear of the beam
Miller says the same caution exists in the United States, along with obstacles such as cost. “There can be hesitancy to use materials if, for example, an engineer could compromise their license or ability to get hired if there is a material failure,” she said. When a failure can end a career, people stay with what they know. Products that carry no structural load, like Modern Mill’s panels, should meet less resistance. “It is often easier to adopt a new floor tile material than it is to adopt a new material for a beam.”
Some states already approve unconventional structural materials, such as earth blocks made from dirt, water and chemical stabilisers, or hemp. A 2025 study proposed mixing rice husk ash, wood ash and rice straw into a cheap, carbon-negative material that could make cement unnecessary.
The husk’s greatest long-term potential may lie in the rice-growing countries of the Global South. Ariana Karamallis, director of global engagement at Build Change, a Colorado-based housing non-profit, says new construction in Africa usually relies on concrete and is often badly built. “It’s like the worst of both worlds,” she said. With materials like rice husk, she argues, builders have to find a balance between affordability, scalability and what communities will accept, and they should avoid testing new techniques on the most vulnerable people.
For now the material is spreading in the United States, where hundreds of new homes use rice husk panelling and the husk also goes into porches and playgrounds. Since the Park City project, Fine has used the panels on five more jobs, with several others planned. He says installation costs slightly more than cedar, but maintenance costs less over time because the panels hold up against moisture, sun and fire. He expects the material to become cheaper than cedar once more builders learn to install it.
“I’m always looking for ways to put a product out that will last a long time, longer than hopefully I’m alive,” he said. The husk evolved to protect a grain for one season. Fine hopes it will protect a house for longer than his lifetime.