How Sustainable is Imported Hemp?
Sustainability of Plant-based Construction Materials
Any construction material is made up of either plants, minerals, or chemicals. Each building block has a unique carbon footprint:
Plant - Mineral - Chemical
Plants (wood, hemp, cellulose) are the best at storing carbon and offsetting the ecological impact of their harvest, processing, and transportation. As a result, plant-based materials typically wind up being net carbon-storing (and thus, carbon-benefiting) materials.
Minerals (steel, concrete, sand) often require significant energy to harvest, process, and transport. As a result, mineral-based materials always wind up being net carbon-emitting materials.
Chemicals (plastic sheeting and membranes, foams) also require significant energy to harvest, process, and transport. As a result, chemical-based materials always wind up being net carbon-emitting materials.
When thinking about sustainability in materials, it’s best to start at the carbon-beneficial end of the spectrum with plants, then move to minerals, and only use chemical based materials when absolutely necessary.
Hemp’s Exceptional Carbon Storing Potential
Hemp just happens to be the best carbon storing biomass solution we have at industrial scale. Hemp is the primary ingredient in hempcrete, an insulation and walling mass made up of hemp and lime. Hempcrete out-performs nearly every other insulation material available. Thanks to it’s widely adaptive use and versatility during installation, hempcrete has come to be known as a solution for addressing carbon in the built environment..
Because of hemp’s exceptional carbon-storing potential, plant harvesting, processing, and transportation to site do not significantly detract from the carbon benefits. Even the carbon impact of adding lime (which undergoes a carbon-intensive manufacturing process) still produces a biocomposite that outperforms nearly all other plant-based materials in terms of carbon benefits. Hempcrete also provides exceptional thermal performance, fire protection, and rot resistance from a naturally safe and non-toxic material.
Carbon Storage of Hempcrete
The answer of precisely how much carbon is stored in hempcrete is measured primarily in the form of an Environmental Product Declaration (EPD). This is a voluntary certification process, completed by third party, used to evaluate the impact of the production and use of a product or material.
In the US, EPDs are not established in the burgeoning hempcrete industry, but in Europe, they are a standard practice. Therefore, we can use that data to compare the impact of using one product or the other, particularly when we are importing those materials.
An EPD does not include the ecological impact of transportation to the US, but that can be calculated. Cargo shipping is rather efficient, compared to ground shipping. For comparison sake, it's more efficient to transport things across the Atlantic (5,000+ miles) by boat than it is to go from the East coast westward past the Mississippi River (1,000 miles) by truck.
Resources and Research
Chris Magwood has done significant research on this, and is working in conjunction with Architecture 2030 to promote natural building materials, including hempcrete and strawbale, as timely and important solutions to address embodied carbon.
In order to help designers and builders make informed decisions, Chris Magwood led the creation of BEAM, an embodied carbon calculator, based on EPD data, geared toward professionals who are looking to use natural materials and be able to quantify them.
HempStone has been privileged to be part of the beta testing for this software, and we are excitedly looking forward to the launch of this program, planned for April 2021..
Calculating Sustainability - a Case Study in Embodied Carbon Accounting
One of the most valuable things about the BEAM calculator is that it allows a designer or builder to see the compounding effects of using not just hempcrete, but a complete palette of natural building materials.
When we evaluated the Howland Hemp House in Goshen, MA, the combination of hempcrete and the generous use of local wood in framing and finishes, offset not only their own embodied carbon, but the embodied carbon of all the other building materials that were put into the house above grade.
That says a lot.
Notice the abundant use of plants in this image:
Timbers, as well as wood board flooring, ceiling, and trim.
The white walls are plastered with minerals:
Lime plaster, which covers more plants; hemp insulation and wood framing.
Chemicals have been avoided altogether except where required for electrical and mechanical systems.
Imagine using 2 materials to counteract the negative impact of every other material in a building. This is the power of plant-based materials, and especially of hemp, which grows in spans of weeks instead of the years needed by softwood.
Further Explorations
Have you heard of the Carbon Smart Materials Palette? It’s a great resource for learning about carbon storing materials. The section on Hempcrete is a good introduction to the material and communicates intelligently about the dynamics at play in the sustainability of the material.
But for a truly deep dive into hempcrete, check out the Hemp Lime Guide by the Healthy Materials Lab.