Founded by Kevin Donahue as KDSE in 2003, Verdant Structural Engineers (VSE) has always been driven by the conviction that green engineering is good engineering. From providing engineering support for the use of products like EcoCocon, Modulina, and Bamcore, to consulting on product designs like Placecraft’s light straw clay panels and Homeland Hempcrete panels, we enjoy offering engineering and building code writing support to facilitate more projects with low-carbon, biobased, and earthen materials. In 2020, we stepped beyond the role of consultant in pursuit of our own novel product development.
With a narrowing window of opportunity to draw back the increasingly dire effects of climate change, there is a clear need to invest efforts in tackling an arena of the built environment that can have an immediate effect: the embodied carbon of building materials. The design and construction industries are beginning to recognize the need to change our conventional practices. But while initiatives like Architecture 2030 and SE2050 strive toward net-zero construction, there simply isn’t an ecosystem of affordable, scalable, and low-to-negative carbon building products available to reach these ambitious goals.
When VSE first started delving into the structural applications of straw and other natural building materials, their primary benefits were seen as low toxicity and reusing agricultural waste. While these are worthy environmental benefits, the transformative environmental impact of straw construction has been revealed more recently with the growing understanding of carbon storage, or embodied carbon. Straw is one of the most intensely carbon-storing building materials in existence. The knowledge that expanding the use of straw in buildings could significantly shift the carbon impacts of buildings has spurred a movement toward expanding straw construction from niche, custom building projects into the densified urban mainstream, where its carbon benefits can have a greater impact.
Over the past 20 years, VSE has built a knowledge base of conventions for what works (and more notably what doesn’t) when it comes to getting a straw-based project built. Each custom project we’ve worked on—of which there have been over 200 encompassing every type of currently used bale building assembly—has led to new questions and engineering puzzles to be solved. The initial form of straw based work that VSE engaged with was straw bale, which comes with some limitations to scalability.
Apart from cost, the primary barrier to scale in bale building is the physical size: due to material handling and storage, building one bale at a time for more than two stories is impractical. Wall thickness is far greater than conventional methods, taking up often-precious square footage in small urban lots.
Straw buildings are heavy! Because earthquake forces are derived directly from building mass, the seismic forces of a straw-insulated building become more significant as the building reaches beyond a single story. Furthermore, if the lateral system is full bales with reinforced plaster, transferring those high seismic forces from story-to-story becomes challenging and impractical for multistory buildings.
A solution to some of the issues of scalability with straw bale construction arrived with the idea of prefabrication. Off-site construction can cut down on the labor of placing individual straw bales and theoretically increase the number of buildings that can be built with straw. The idea has been circulating through the community for a while, but Craig White’s1 2017 California Straw Building Association (CASBA ) conference keynote presentation served as a turning point for a number of designers, particularly on the U.S. west coast. After his presentation on the potential of prefabricated straw, novel designs and methods for building with straw started showing up at VSE’s door.
These prefabricated straw projects have had a broad range of ideas, applications, and project specific needs. They allowed VSE to experience a wide variety of approaches to prefabricated straw building from the inside out. One thing many of them had in common—they didn’t get built. This rarely had to do with structural issues or limitations, but other practicalities relating to the individual project. This unfortunately, is also common for all types of new ideas in the alternative natural building space. For example, one project sought to contain bales in a steel frame to be used as exterior and party walls in a multi-unit building at the Esalen Institute in Big Sur, California. This ran into issues with contested acoustic issues. Another project had the idea of building plywood boxes with full bales inside of them onsite. Ultimately, the builder didn’t see this as any easier than building it bale by bale on the foundation. One successful project, with the architectural design and construction by Boa Constructor, involved filling wood frames with re-formed half bales [see How To Build A Straw Panel In Your Backyard on page 44]. This approach had a lot of positive attributes, but still involved a lot of work processing individual bales to
fill the frames.
One method that has gotten a fair amount of traction is the “bales on end between studs” (BOEBS). Although this system is not prefabricated, it uses conventional framing methods which overcome previous full bale scalability issues, particularly those dealing with contractor and design professional familiarity. This system accounts for more than 50% of all recent full bale projects VSE has designed. Its subtleties have offered quality insight into detailing straw within a conventional wood building assembly.
In April 2020, StopWaste funded a multidisciplinary team including VSE, ARUP design group, CASBA, and Arkin Tilt Architects to write a report on a mid-rise mixed use carbon storing concept project. Panelized straw and BOEBS techniques were some of the main features we arrived at to achieve the building’s goals. Beyond that, it solidified our collaboration with natural materials specialist Massey Burke, who is now a member of the core team developing the Verdant Panel. You can find the East Bay Carbon Storing Building Pilot Project Report on Carbon Leadership Forum (CLF) Bay Area’s Website.
When we heard about the EPA’s Small Business Innovation Research (SBIR) grants, we assumed it would be a great opportunity for one of the many designers or builders we knew operating with the desire to streamline straw construction. However, it became quickly apparent that we had the resources to pursue this sort of project that others in the natural building space lacked—the grant wasn’t available for non-profits, like CASBA, and we had the business size and budget available for the difficult and involved government grant process others couldn’t afford or simply weren’t interested in. Beyond that, we had an aggregate of lessons learned through the many attempts of our clients and others to streamline straw construction.
Choosing to apply for the EPA’s SBIR grant in August of 2020 was a bold step into a new space for us. We approached the development of a prefabricated straw panel without project- or client-specific needs, and applied VSE’s extensive straw design experience, with the underlying question—what would best help to accelerate the urbanization and wide scale acceptance of straw? At the time of our grant pursuit we were not aware of the scope of New Frameworks panel development, that EcoCocon was attempting to establish a U.S. presence, or the existence of Croft. We recommend people explore these products too, but believe we are working on a system that approaches straw panel design differently.
We felt that the panels needed to fulfill all of the following considerations:
-
Achieve a higher R-value to be thinner and lighter
-
Able to receive a variety of interior and exterior finishes
-
Sized and configured to fit conventional wood framing, making it accessible to potential contractors
-
Cost-competitive with typical wood frame or foam SIP construction
-
Easily strengthened for higher seismic performance
We recognized that prefabrication also presented the opportunity to use and manipulate the characteristics of straw beyond the form it takes in a bale, and that this could be the key to increasing the thermal performance, which is at the core of achieving several of our design variables. Another crucial variable is the speed and method of manufacturing, which will help us bring down cost relative to other bale building methods. Once manufacturing at scale, all levels of panel materials processing and fabrication will involve mechanization for speed and efficiency of labor.
To get to a primarily bio-based material market we need to create a strong base of consumer confidence. The federal and local governments are already starting to acknowledge and fund the need for low-embodied carbon building materials. The Inflation Reduction Act of 2022 included many provisions toward reducing carbon emissions in the built environment, including a $27 billion allocation for the Environmental Protection Agency to enable zero-emission technologies and projects that reduce or avoid greenhouse gas emissions. Some of this money is going toward the development of Environmental Product Declarations. In 2022, the USDA launched a Bioproduct Pilot Program, which granted $9.5 million to support the scale-up of sustainable bioproduct manufacturing and development of value-added products from agricultural commodities in the United States. These and other initiatives lend both financial support and marketing credibility to emerging new materials.
We also view an industry association of well-intended, mission driven, carbon-storing products as a critical way to collectively boost consumer confidence and broader adoption of these products. Early initiatives we’ve envisioned for a trade association include technical research, testing, EPD development, and collaborative marketing for advancing the adoption of panelized straw-based wall systems. It can be faster and easier for a consumer to find confidence in a material type they haven’t used before when it is one of a suite of well performing products, rather than a unique product that is quite different from most other options on the market. Three or more product bids are often needed for government or similar projects, and an industry association can help facilitate the existence of such a market rather than allowing misperceived competitive fears to pit early innovators against each other.
We’re still at the beginning of the Verdant Panel’s story and are now ready for beta projects in California! Reach us at panel@verdantstructural.com to see if your project would be a good fit. We are in an active $500,000 – $1,000,000 SEED funding phase for the Verdant Panel under Verdant Building Products and we are looking for like minded, mission-oriented partners like you! Please be in touch if you would like to build a beta Verdant Panel project, need engineering support for any type of straw building across the US, or if you would like more information about these or future investment opportunities.
RACHEL COHEN is a structural engineer in the San Francisco Bay Area who is motivated by a love for design and a commitment to creating a more environmentally-minded built environment.
ANTHONY DENTE is a co-founder of Verdant Building Products, Principal at Verdant Structural Engineers, and Vice President of the Cob Research Institute. He was the lead engineer for the Cob (Monolithic Adobe) and Hemp-Lime (Hempcrete) IRC appendices, and contributed to many other natural building testing, code and product advancements. He is also a co-author of Essential Cob Construction released January 2024.
