TechnologyWhy is Robert Downey Jr. making buildings with hemp?

Why is Robert Downey Jr. making buildings with hemp?

Hemp emerges as a sustainable building material.


When Robert Downey Jr. was selecting building materials for a new project, he insisted on building with hemp.

The Iron Man movie star had recently launched a venture capital firm—The Footprint Coalition—dedicated to investing in sustainable solutions. As his team was reviewing plans for a new property, Downey asked if it was possible to make the project more sustainable. His team suggested HempWool, a hemp-based building material that can be used in lieu of fiberglass and other fossil fuel-intensive materials.

This marked the first time HempWool was used in a commercial building in the U.S.

Mattie Mead, founder of Hempitecture—the Idaho-based company that manufactures HempWool and other building materials—says that hemp is emerging as a top choice for sustainable construction.

Sustainable building materials face several obstacles to scalability: cost, awareness, availability, ease of use, building codes and government regulations

“We’re seeing huge growth in the field, and we’re trying to keep up with demand,” he says. “HempWool in particular is so easily implementable that there’s a real scalability to it. And that’s really attractive, because it means we’re able to get plant-based building materials in more homes—which, at the end of the day, is what’s really important to us.”

As a building material, hemp offers several advantages.

First, it’s durable, flexible, fireproof and thermal-resistant (meaning it retains the temperature within the structure). Also, it resists mold and vermin.

But what makes products like HempWool stand apart is that they’re low carbon or even carbon-negative, meaning that the hemp grown to produce them removes more carbon from the air during its growth cycle than the amount of carbon released during processing. This makes hemp significantly more sustainable than most traditional building materials.

“I really became interested in biobased building materials when I learned that about forty percent of our carbon footprint comes from the construction and operation of buildings,” Mead says. “Also, a huge amount of building materials end up going to the landfill.”

Hempitecture isn’t the only U.S. company focused on hemp-based building materials. HempWood, headquartered in Kentucky, offers a hemp-based alternative to traditional wood products. Meanwhile, several businesses—including Hempitecture—are producing hemplime (or hempcrete), a mixture of hemp hurds, lime and water that can be used to construct buildings.

One of the benefits of HempWool is that it’s approachable for builders. It doesn’t require any special training to install.

Hemp has long been used as a building material around the world—it’s currently regaining popularity in Europe—but, until recently, it couldn’t be legally produced in many U.S. states. The 2018 Farm Bill changed that, legalizing the industrial production of hemp at the federal level. Still, many states were slow to update their own regulations. Idaho, the home of Hempitecture, was the last to legalize production, in April of 2021.

In the past, Mead says that his business had to import nearly all of its raw materials, which added to production costs. He hopes that the new regulations will lead to cheaper materials.

“Right now, we’re at a turning point for the availability of this material in the United States,” he says.

How can hemp-based building materials scale-up?

Limited supplies and high costs aren’t the only issues the industry is facing.

There’s also the matter of code. When a building is constructed, an inspector has to approve the materials used. However, most of the current building codes in the United States were written before hemp-based technologies were popularized.

Today, an inspector might deny a project because there isn’t enough data showing that the materials have been tested for structural integrity, fire-resistance and other attributes. For those wishing to build with hemp, the data can’t come soon enough.

And then there’s the knowledge gap. According to Mead, many of the people who might use hemplime and other hemp technologies simply don’t know how. These materials are nuanced, and they haven’t been circulating through the market long enough for a community of experts to emerge. This makes it difficult for demand to grow.

Hempitecture has taken a hands-on approach to their industry’s shortcomings. Where data is lacking, they’ve commissioned independent studies. In 2020, they proved—via a third-party lab—that hemplime is fireproof. (On a scale of zero to 450, with 450 being the most flammable, hemplime scored a zero.) Now, if someone wants to build with hemplime, they can use this data to prove that the material is fireproof.

Mead says there’s more work ahead.

Tommy Gibbons and Mattie Mead, founders of Hempitecture, met in high school. Mead brings knowledge in building and environmental science, while Gibbons brings experience in corporate finance and startups.

“That’s one element of code, but there are so many more—thermo-resistance, structural integrity. There are a lot of codes that need to be addressed to make this more implementable. That’s a big roadblock.”

In an effort to overcome one of hemp’s other roadblocks—the knowledge gap—Mead’s business has begun hosting training courses at their headquarters in Sun Valley, Idaho. People from across the U.S. meet with Mead and other experts to learn techniques for building with hemplime.

“What we’re trying to do is take what we know and democratize it—share everything,” he says. “On the one hand, it benefits our business, creating an ecosystem of future buyers. But really, we’re just trying to grow the industry.”

As a more sustainable building material, it will take time for hemp to reach its full potential. There are still challenges, like a lack of research and trade knowledge, government regulations, high costs and limited supplies.

But there are signs of a growing market. While COVID-19 forced Hempitecture to cancel many of their 2020 training courses, demand is high for 2021.

“We’re basically sold out for the year,” Mead says.

Troy Kelleher
Troy is a marketing expert with a background in investigative journalism, where he's written for Chicago Tribune and Sun-Times Media Group. He's passionate about storytelling around cannabis, particularly around it's utility as a resource in the modern world.


  1. How exciting! Since I started research into tiny homes and van living, I’ve seen a lot of people using hemp insulation like HempWool. I hope to use it in my own home one day.


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