The University of Manitoba, Bio-Systems Engineering Department has been testing hemp building materials for the past year. Masters student Jeremy Pinkos, under the guidance of Professor Kris Dick, has been examining different types of hemp-lime walls and assessing their insulative properties, airtightness, density, hygroscopicity, moisture resistance and structural properties. The research is being carried out at the U of M’s Alternative Village, a unique outdoor laboratory dedicated to research, testing, and training related to renewable energy technologies and building envelope systems in Canada. (The Village also happens to be home to one of the largest straw-bale buildings in Canada as well.)
Biostruct has begun testing our material at the U of M this year. Of course, the testing of hemp building materials is nothing new; in Europe, the industry has been growing for over 15 years, and many products have already received third-party certification there. While it’s true that hemp building materials are fairly new to the North American market, there are a few owner-built homes throughout Canada. There are also some houses in North Carolina that have been constructed using imported European hemp and lime materials.
As a building material, hemp-lime has many favourable attributes that are especially valuable in today’s greener building marketplace.
Hemp bio-masonry walls are:
–Fire- and insect-resistant.
–Non-brittle: Since the material lacks the brittleness of cement, it eliminates the need for expansion joints.
–Insulating: Values equal or surpass those of conventional products (R-value of over 2.5 per inch).
–Hygroscopic (vapor permeable, while being impermeable to liquid water): Just as our bodies need to “breathe” by releasing moisture and toxins through our skin, our homes–and more particularly, the walls of our homes–should also be able to transmit water vapour.
Most of the houses being built today are completely sealed with vapour barriers in order to prevent moisture transfer. However, water often finds a way to get inside those seals – by capillary action, for example. And since moisture that enters a sealed wall has nowhere to go, the result is mold, decay and rot. In the case of hemp bio-masonry, the solid mass construction eliminates the air gaps that can lower R-value, even as the material itself facilitates moisture transfer. This breathability is what prevents the buildup of mold and mildew inside the structure.
There are a few fairly common misconceptions about hemp-lime. Some blogs or internet sites claim that “hempcrete” (as they refer to it) is 7 to 10 times stronger than concrete, when in fact, the compressive strength of hemp-lime walls is quite low. This is due to the fact that the product has been designed to be a non-loadbearing, insulating bio-masonry material. (Some people have used hemp to reinforce concrete, which could increase the concrete’s strength, but this is not usually the case with hemp wall systems.) Some of the misunderstandings might be due to the fact that the word “hempcrete” suggests a hemp-reinforced concrete. To avoid such confusion, Biostruct as a company has avoided using that name; we prefer to use the more accurate terms “hemp-lime construction” and “hemp bio-masonry materials”.
Hemp-lime walls use what natural building expert George Swanson calls “living cements”, meaning they bind well with plant cellulose. Examples include high calcium lime and magnesium oxide. The more commonly used alternative, Portland cement, actually repels cellulose, and must therefore be combined with plastic binders to permit adherence to building substrates. In turn, these petroleum-based binders make the concrete more hydrophilic, locking in moisture and thereby increasing the risk of mold and mildew formation. Another built-in advantage of natural lime, making it a more attractive option than concrete in this case, relates to its curing cycle. As the hemp-lime in a building reverts back to limestone, it sequesters CO2 from the air, thus rendering the structure virtually carbon-neutral. On the other hand, the production of Portland cement requires a much more energy intensive process, and the final product does not provide the added benefit of re-absorbing the CO2 that was previously released.
Agricultural hemp, which is capable of sequestering over 10 tonnes of carbon dioxide per acre, is considered one of the most economical crops a farmer can grow. Moreover, since most of the hemp currently grown in Canada is used in food production, hemp builders needing fibre can make use of an already available by-product. Until recently, the market for Canadian hemp fibre products has been limited, due in part to the lack of secondary processing facilities. Now that the industry is taking off, however, the hemp fibre that was originally being burned or used as animal bedding can be used to create multiple useful products.
Access to new technologies and instruments–for example, life-cycle assessments or LCAs–are revealing both the benefits and drawbacks of various “advances” in green building (including the dawning use of nano-materials, which we discussed previously) and are thus helping to establish the legitimacy of these innovations–or lack thereof. At the same time, municipalities are increasingly taking into account the amount of carbon that is embodied in the structures they build. The desirable features of hemp-lime building systems–in particular, their relatively small carbon footprint in comparison to that of other systems–are bound to get them noticed. We at Biostruct believe they are destined to take a starring role in the future of building.
THE FUTURE OF HEMP BUILDING: IT’S TIME TO START BUILDING BETTER
Stay tuned for more details on the work being done at the University of Manitoba on hemp building materials. Updates will soon be provided as well on the prefab hemp wall systems we are developing in cooperation with SAIT Polytechnic in Alberta. Any parties/post-secondary institutions that are interested in partnering with us in building (as well as testing) some structures in B.C. are invited to contact us.
(Photos: Top two photos courtesy of Erik Eising)