Updated: Sep 16
By Derek Markham on TreeHugger.com
When it comes to industrial hemp production, the US lags far behind many other nations, but if domestic hemp cultivation becomes completely legal here, green builders could have access to an affordable and sustainable construction material, namely hempcrete.
Hempcrete, which sounds rather like a made up hippie word instead of an alternative building material, is a fascinating green construction option that uses the hurds, or inner woody core of the hemp stalk (as opposed to the bast fibers, which are used for textiles and cordage), in a mineral matrix, to form a non-toxic, carbon-negative, and energy-efficient material. Hempcrete isn't that new, but isn't very widely used at the moment, especially in the US, most likely due to the fact that the hemp has to be imported, as it's illegal to grow here.
A hempcrete design & build startup, Hempitecture, wants to see a "new archetype in sustainability" in building in the US, and to take the movement forward, they're working toward the construction of the first non-residential hemp building in the US. To help get the project, which will be built at Idaho Base Camp (IBC), off the ground, the team has turned to crowdfunding with a Kickstarter campaign, which will help to underwrite the additional costs (due to having to import the hemp) of building with hempcrete.
Hempitecture grew out of an earth building research project at Hobart and William Smith Colleges in Geneva, New York, and along with the hempcrete building project, is now pursuing their vision of creating a proprietary hempcrete binding matrix that can eventually be sourced from the US and sold for the domestic building market.
Although I'm a fan of hemp as a regenerative, low-impact, and incredibly useful plant, I knew next to nothing about the use of hempcrete in green building until just a short time ago, so I had a few questions about it, which Matthew Mead, founder & CEO of Hempitecture, was gracious enough to answer for me.
Q: Why did you end up focusing on using hemp as an earth building material, as opposed to cob or adobe?
Mead: The Hempitecture concept emerged from a research project I conducted at Hobart and William Smith Colleges that examined different types of earth building methods. Through this research I disseminated the different strategies into categories such as ease of construction, availability of material, environmental impact, and market viability. Cob and strawbale building techniques are great, but they are incredibly time intensive and most usually they lend to a discerning aesthetic.
Hemp building is more versatile, it can be cast in any archetype from contemporary, to rustic, to traditional. What really tipped the scales in favor of hemp building is that hemp is rapidly renewable and absorbs carbon dioxide at an incredible rate. During its growth, it actually contributes to the soil's biodiversity, thus hemp enriches the immediate environment that it is grown, while subsequently being utilized as a non-toxic, energy efficient building material to enrich the home environment. Q: I understand that because you have to import the hemp for this project, the expected cost is higher than if you had access to domestic hemp. How does the cost compare with building a conventional building that had the same insulative qualities?
Mead: Hemp building can be an affordable housing solution given local availability of building grade hemp. The United States is the only industrialized nation on earth that bans the production of industrial hemp, thus we're unable to utilize it in a cost-effective manner as it must be imported. There are many examples across the world of hemp building being utilized as affordable green housing. There is the Clayfields social housing in Suffolk England, there is a project in Scotland where they are building 20 houses, all from hemp. The list goes on and on. These projects all materialized under two main tenets, cost & environmental impact. Hemp building meets both those requirements when the proximity principle is met.
Q: Once industrial hemp is legalized and in production in the US, do have any idea of what the cost to build with hempcrete would be (when compared to a conventional building)?
Mead: It is difficult to say how the cost of hemp construction will change once domestic hemp is produced. There is critical infrastructure needed to get industrial hemp from farm to building material, primarily a processing facility. The hemp must be decorticated, separating the woody core from the long fibers. The woody core is then used in hempcrete. I believe we are close to realizing an affordable North American hemp source. Our neighbor Canada has long since recognized the incredible potential of industrial hemp, and are currently concluding a multi-million dollar hemp decortication facility, strategically located just north of the US border.
Q: Even if hempcrete were initially more expensive to build with, what type of long-term savings could owners expect to see, in terms of reduced energy use for heating and cooling? In other words, what would the return on investment be for building with hempcrete versus traditional construction?
Mead: The return on an investment in a building project is dependent on so many different variables. Hemp walls are incredibly insulating but its potential can be maximized through thoughtful design. We have designed our current project in response to comprehensive solar studies, blocking out the bad sun that overheats and bringing in the good sun that will bring the building to a comfortable temperature. Conventional building over time can become increasingly less energy efficient given the degradation of insulation over time. Hemp Building will stand the test of time overall significantly reducing the energy consumption of the structure, but of course with proper design principles followed.
Q: Are there good precedents for hempcrete in building codes and going through the permitting process, or do potential builders currently have to spend a lot of time educating and persuading local authorities of the appropriateness and safety of building with this material before being approved?
Mead: Potential hemp builders can go through some serious headaches to move forward with building codes and permitting. There is almost always an aspect of education when discussing hemp building in the US, and some states or jurisdictions are more receptive while others are less. A beautiful home was recently constructed from hemp in Sun Valley, nearby where our project is, and the builder reported that it was extremely difficult to work with the county. Fortunately for us, we are building in Custer County with a population of around 4,000. There is no building inspector, minimal requirements, and a precedent has already been established nearby in Sun Valley.
Q: Does the hempcrete continue to absorb CO2 after construction, even after being covered with a "skin" or cladding layer?
Mead: Hempcrete is continually absorbing CO2 during the curing process. The lime in the Hempcrete mixture requires CO2 for complete solidifcation. Hempcrete is always finished with a breathable layer such as a lime-based render. If finished with cladding, there is a space left for air to interact with the hempcrete wall, allowing this process to continue.
Q: Does the use of hempcrete within a stick or timber frame require different building and design techniques to account for any additional weight of the material? Or can it be used as infill in a traditional stick frame building without major changes to the design?
Mead: Hempcrete can be as versatile as your design calls for. Most typically it is infilled within a traditional stick frame. We are using a timber frame to appeal to a high mountain aesthetic. Weight is not much of a consideration, as hempcrete is lightweight.
Q: Your Kickstarter page states that your bigger vision is "creating a proprietary hempcrete binding matrix" sourced and sold in the US. What are your next steps in that vision?
Mead: To perform research and development, we need money, mentorship, and a climate controlled space. We're currently in discussion with the Ketchum Innovation Center, an incubator and accelerator for Sun Valley based entrepreneurs to utilize both their space and mentorship connections. We are hoping to reach our Kickstarter goal and launch a stretch goal which will go towards some preliminary funding allowing us to really accomplish a lot in the KIC. Of course this process is extensive and time intensive and we ultimately project additional funding will be critical. Following our project at Idaho BaseCamp, we intend to really dig in to this R&D concept and would be open to outside funding such as investments.
Q: Will you be documenting the building techniques to educate prospective hempcrete builders and the hemp-curious?
Q: What's next for Hempitecture after the IBC building?
Mead: Hempitecture co-founder and lead designer will be attending the masters of Architecture program at University of Virginia in fall of 2015 with a focus on sustainable design. Following this Tyler will rejoin Hempitecture with an expanded skillset that will allow Hempitecture to autonomously conduct design processes and projects without the current framework of mentorship we currently have. In the interim, we intend to collaborate with other architects, engineers, and contractors to enact more hemp building projects in the US. Following the IBC build we will switch gears to furthering the R&D concept at the KIC. We are also interested in expanding this research in an academic setting. There are many different academic pathways in which our larger vision can materialize.
If you support the wider adoption of hempcrete and other hemp building materials, consider chipping in to Hempitecture's Kickstarter campaign, and follow along on their hemp startup journey on Twitter or Facebook.