Hempcrete: Making Sustainable, Stylish, and Award-Winning Homes
Most people aren’t particularly surprised to learn that hemp can be turned into a variety of foods, beauty, and wellness products, and it’s not much of a stretch to imagine the plant’s fibers being processed into rope or cloth. But did you know that hemp is so versatile that you can actually build a house with it? One that’s both sustainable and stylish. One that wins building awards (more about that in a minute). Here’s why hemp is becoming increasingly popular within the building industry.
A Long History of Building with Hemp
Building with hemp is not a new idea. Around the world, there’s evidence that hemp has been used in construction for hundreds of years. For example, according to an article in Architect Magazine, it was utilized by ancient Roman engineers. In Japan, there’s a national heritage site in Nagano prefecture, where you can visit a hemp house that was built 1698 and is still standing.
Why has hemp construction persisted throughout history? Because hemp is an amazing building material that not only makes a great house, but has a long list of environmental benefits too.
Advantages of Hempcrete
The most common way to incorporate hemp into a structure is with hempcrete. This lightweight, insulating substance can be used in walls, floors, and ceilings, and can replace traditional materials like fiberglass or concrete (it’s not load-bearing though). The National Hemp Association (NHA) lists numerous benefits to using hempcrete: it’s non-toxic, energy efficient, resistant to flame, water and pests, and it’s strong, lightweight, breathable, and an excellent insulator.
Using hemp also helps the environment. As NHA points out, “Modern day building materials are either mined from the earth or harvested from centuries old forests.” These forests and natural resources are difficult to replace because they usually form over many years, however hemp is a much more sustainable choice because it grows to maturity in a mere four months (and requires little water or pesticide use). “Hemp crops can be harvested annually in perpetuity,” points out NHA.
Not only that, but hemp has a lower carbon footprint than many other construction materials. The building industry uses a lot of energy and creates a lot of CO2 emissions. This happens during the construction phase—for example the manufacture of concrete is a significant source of carbon emissions—and also later when the people who live or work in a building use energy for things like heating and cooling. According to the International Energy Agency, the buildings and buildings construction sectors account for 36 percent of the world’s energy consumption and almost 40 percent of total CO2 emissions.
Hemp is much more environmentally friendly. When it grows, hemp actually absorbs a significant amount of CO2 from the atmosphere. Hempcrete locks that CO2 away for the life of the building, keeping it out of the atmosphere, making it a carbon-negative building material. Furthermore, hempcrete is a better insulator than traditional building materials, meaning that a hempcrete house requires less energy for heating and cooling.
The Award-Winning Mudgee Hemp House
How exactly do you build a house out of hemp, and what’s it like to live inside? I asked Dick Clarke, who knows a lot about building with hempcrete. Clarke is an Accredited Building Designer and principal of the sustainable architectural design company, Envirotecture, in New South Wales, Australia. He is also a director for the Australian Hemp Masonry Company, and editor of the book How to Rethink Building Materials. Clarke designed the well-known Mudgee Hempcrete House, which is located in Mudgee, New South Wales. This beautiful and sustainable home won two major awards at the 2018 National Design Awards for the Building Designers Association of Australia: The Paul Dass Memorial Prize, which is for outstanding achievement in building design, and the Best Residential Building title. I asked Clarke for a bit more information about hemp homes.
What is hempcrete made of and how is it used in construction?
Dick Clarke: It is technically ‘hemp-lime composite’, made from the chopped woody inner stem of the industrial hemp plant, called ‘hurd’, mixed with hydrated lime, and water. Sand may be added for extra strength and thermal mass. It undergoes a pozzolanic reaction between the calcium carbonate in the lime and the silica in the hurd, which converts to a form vaguely like petrified wood.
What’s it like to live in a house made of hempcrete? Does it look or feel different to one made with traditional building materials?
Clarke: They are delightful to live in, due to their tight temperature control (if all other aspects of the building are correct), excellent internal humidity control, and acoustic characteristics. The look is like any other rendered masonry building, unless internal walls are left ‘off-form’ in which case they have delightful granular look.
What about the environmental benefits of using this material in construction?
Clarke: Farming: nitrogen fixes the soil, [hemp] requires no irrigation, pesticides or herbicides, less diesel inputs for the farmer, 1 to 2 crops per year.
Processing: Low energy, no heat or chemicals involved.
Anything else that the average person might not know about building with hemp?
Clarke: It’s termite resistant (a big issue here) and bushfire proof (also a big issue).
How about affordability? How does the cost of hempcrete compare to other building materials?
Clarke: In-situ hempcrete is about the same as well insulated brick veneer (Australia’s most common system. It’s awful BTW.)
Have you designed many hempcrete buildings overall?
Clarke: About a dozen so far.
Is this material becoming more popular?
Clarke: Yes. We have seen a steady increase in interest over the last 5 years.
Gradually Gaining Popularity in the United States
Despite all of its benefits, building with hemp has been slower to catch on in the United States. According to a recent New York Times article, in total there are only about 50 hemp houses in the entire U.S. The first house to be built from hempcrete in modern U.S. history was in 2010 in North Carolina. However, as hemp slowly loses some of its stigma and people begin to recognize just how many benefits it has, you are likely to see a lot more homes made from this amazing plant.