Sequestering carbon and reducing energy consumption with hempcrete
In 2007, I bought 37 rural acres in Damascus, Pennsylvania, that included two post-and-beam barns, a 1910 farmhouse, and an old, sagging chicken coop. My long-delayed plan to convert the chicken coop to my new pottery studio finally got started last year.
Twelve years ago, I dismantled my Hoboken studio located in the old Eureka Theater at 258 Newark Street. The firebricks from my former gas kiln are stacked in the shed behind the small barn. My kickwheel, pugmill, and other pottery equipment, plus clay and glaze materials, have been stored in the two barns, gathering dust.
The chicken coop had character, but the required exterior insulation and cladding would destroy most of its historic value and appearance. So after several lengthy discussions with my carpenter, I made the decision to take down the structure.
The new building is modeled after the old chicken coop, with the same footprint. But unlike the old structure, the walls will be a foot thick and made of hempcrete. If you are not familiar with hempcrete, you are not alone. Neither was I until last year when my friend Jamie Stunkard, the owner of Nature’s Grace, a health food store in Honesdale, Pennsylvania, told me about his hempcrete project. Hempcrete may be the antidote to modern building methods and materials.
An all-natural, non-toxic material, hempcrete consists of the chopped cellulose stalk of the industrial hemp plant mixed with a lime-based binder. The fast-growing hemp plant soaks up carbon dioxide and once mixed with lime, it continues to absorb carbon, creating a structure whose chemical composition is calcium carbonate, the same as limestone. As a result, it is a carbon-negative building material.
The thermal mass of hempcrete allows it to store heat and protect against temperature fluctuations. Foot-thick walls provide superior insulation, thus reducing energy consumption for both heating and cooling. (The R-value is rated between R2.5 and R3 per inch.) In addition, the walls are breathable and can absorb and release moisture, thus optimizing indoor air quality. The lime binder makes the hempcrete fire resistant. It also repels vermin.
A few weeks ago, aided by the mild winter weather, the footings were poured and then the frost walls. The slab will have to wait for warmer weather in early spring. Then my carpenter will erect the 2×4 framing for the walls and the 2×8 roof rafters.
The studio measures 50 feet long and 14 feet wide and will require about 750 cubic feet of hempcrete. Casting this mix around the 2×4 frame will be a labor-intensive week-long project. Cameron Macintosh of Americhanvre in Lancaster, Pennsylvania will come up with his drum mixer and supervise a crew of people that I am putting together.
Once the hempcrete walls have dried out sufficiently, several coats of lime plaster will be applied inside and out. This building method eliminates the need for sheet rock, plastic vapor barriers, cladding and paint.
Once my studio is complete, I will get to work making earthenware tiles for my kitchen, a DIY project that I have been working on for several years. I have started to dream about wheel-thrown stoneware and have drawn up designs for a small downdraft kiln. This all would have happened sooner except for financial constraints, and a day job that continues to interfere with my many other projects.
I will provide an update once the studio is finished. I am hoping this structure will be an inspiration to others who learn the many advantages of using hempcrete.
Ressources
The Hempcrete Book – Designing and building with hemp-lime, William Stanwix and Alex Sparrow (Green Books, 2014)
Hemp Concrete Walls (R30 + Fireproof) – You Won’t Believe How They Built This House!
Americhanvre Cast Hemp
