Biogenic Building Materials 101 – by Joel Caldwell

This year I had the opportunity to direct my first film for Patagonia. I’ve been working on it since February and today we deliver the completed film 💃 The full banana goes live October 23rd, but here is the trailer. 

The basic premise of the film: the first group in North America to grow their own hemp, process it into usable fiber, and use it to build high performing, eco-friendly houses is one of the smallest tribes in North America. Faced with a housing crisis—after ~180 years of oppression, the loss of a 29 million acre territory, enduring the largest mass execution in US history, and being forced onto a three square mile reservation consisting of only sand—the Cansa’yapi (Lower Sioux Indian Community) turned to hemp to build healthy homes and resume their traditional role as environmental stewards.  

Biogenic building materials have become an obsession ever since I met Charleston-based architect, April Magill, in the fall of 2022. Thanks to April, I saw the potential for a mass adoption of these new (old?) materials and the opportunity to literally build our way towards a better climate.

I’ll explain.

The pickle: The construction sector is the third largest emitter of CO2 in the world. Around 45% of landfills in the US are full of construction debris. The way we build is a BIG PROBLEM. But, we also have a major affordable housing crisis. In South Carolina, where I live, there are about 70,000 subsidized housing units, enough to serve only twenty percent of low-income renters—a problem that is not unique to this state. ANOTHER BIG PROBLEM (hang in there, good stuff coming). 

Having understood the building sector to be an incredibly large emitter of CO2, I’ve felt pretty pessimistic about our ability to accommodate an exploding population while also meeting our climate goals. We’ve probably all heard about “green building?” Up to this point, the green building movement has focused almost exclusively on “operational energy efficiency,” (i.e., low emissions once a building is built) but largely turned a blind eye to the extremely energy-intensive components (i.e., steel and concrete) as well as the highly toxic materials (i.e., acrylic and polycarbonate plastics, adhesives, and fiberglass insulation) used to build these super efficient homes. 

The embodied carbon is the sleeper (embodied carbon= the carbon dioxide emissions associated with making something. Example: A cooler full of ice on a hot-ass Charleston summer day has the embodied carbon of all the energy it took to turn that water into the ice you enjoy.) 

According to a recent report by the Rocky Mountain Institute, “up-front embodied carbon emissions from building construction in the United States is estimated at up to 370 million tons of CO2e annually, or about 6% of total US emissions per year.” The report then goes on to say, “This long-invisible source of emissions is large — comparable to all of California’s current annual emissions.” (gulp)

A few years ago I attended a hempcrete building workshop put on by Charleston-based architect and founder of the Root Down Building Collective, April Magill. At April’s workshop, I felt a door to a climate solution slide open in my mind / a light turned on / suddenly I understood. Let me explain.

Conventional building products come from the environment (logged from forests, mined from the earth). We heat, beat, and treat these raw materials with chemicals—each step requiring energy—to suit our needs. What if instead of expending all that energy, we built with natural materials and allowed the energy to come from the sun? 

A hemp example: In South Carolina’s humid, subtropical climate, farmers can grow two crops of industrial hemp a year (hemp can be grown nearly everywhere, but it’s particularly vigorous in hotter, wetter environments). One of the fastest growing plants on Earth, hemp explodes from a seed smaller than a coffee bean to well overhead in just ninety days, absorbing CO2 all the while and gaining enough biomass to fill a tractor trailer every five acres (you farmers out there know what I’m talking about). As the hemp crop grows, it is sequestering carbon from the atmosphere (isn’t that magic?? A plant is the manifestation of atmospheric carbon in solid form. Wowow.)

Hempcrete, or “hemp-lime,” is a non-structural, eco-friendly building material. Mixing hemp fiber and water with a lime binder creates a light-weight and durable material that can be used to insulate exterior walls and ceilings. While conventional products like fiberglass insulation are both energy intensive and made with petrochemicals, hemp pulls carbon from the atmosphere during growth and then locks it away for the duration of the building’s lifetime, effectively making the home a carbon bank. 

SO THAT MEANS: building with hempcrete—and other biogenic materials—makes it possible to tie up more carbon within your home than you are emitting as a result of extraction, manufacturing, and transportation of materials to the construction site. This is how we build our way towards a healthier climate!

So to recap, by utilizing plant-based materials we can create carbon-negative buildings. By adopting these materials at scale, we can leave our relatively slow-growing forests to do all their wonderful and essential forest-y things (like supporting wildlife, providing us oxygen, the creation of healthy hydrologic cycles, building functioning ecosystems, etc..) and harness fast-growing lignocellulosic materials (think the wood core of hemp / sunflower / corn stalk, etc..) to build homes and store CO2. Instead of growing crop after energy rich crop, only to let the majority of the plant lay in the field and return to atmospheric CO2, we can lock it away in newly built and desperately needed homes year after year. 

(In your mind you see a cartoon of atmosphere being pulled from the sky and stuck into homes all over the world. A great imbalance being rebalanced. I see it too!)

Natural building practitioners all over the world have proven that high performing homes can be built from natural materials. Now we need to bring these alternative solutions to scale. Doing so would allow us to quickly curb emissions. Per the Rocky Mountain Institute report, “Bio-based materials may represent our best hope for radical decarbonisation through the responsible management of carbon cycles. The shift towards properly managed bio-based materials could lead to compounded emission savings in the sector of up to 40 per cent by 2050 in many regions.”

This isn’t a fantasy. Here are some examples from around the world: 

*RMI report and photos of existing biogenic buildings thanks to Chris Magwood.