Hempcrete - Hemp Building Materials - Hemp For Houses
by Rolf B. Priesnitz, Hemphasis.net & Wikipedia
Houses built from hemp have been found to use less energy, create less waste and take less fuel to heat than conventionally constructed homes.
Hemp is perhaps best known for its Omega-3 and -6 fatty acids that make it a great addition to a healthy diet, and as a cotton substitute in ecologically-sound clothing and bedding. But it is also a versatile, environmentally-sound building material.
A hemp crop can be grown without the use of herbicides or insecticides and produces up to four tonnes of material per acre per year. Hemp is categorized as a bast fiber crop. It has a stem consisting of an outer skin containing long, strong fibers and a hollow wood-like core or pith. Processing the stems results in two materials: hurds and fibers, both of which have properties that make them extremely useful in building construction.
A variety of wood-like products, such as fiberboard, roofing tiles, wallboard, paneling, insulation and bricks, can be made from the compressed hurds. The fibers can also be used like straw in bale wall construction or with mud in a sort of modified cob style of building.
Foundations can be made out of hemp hurds. A hemp plywood frame is filled with a hemp hurds combined with lime, sand, plaster, some cement and enough water to dampen, and then let to set for a day and to harden for a week. A sixth century hemp-reinforced bridge in France is testimony to the stone-like strength and durability of this material, which has come to be known as “hempcrete”.
Hemp building boosters claim that hempcrete foundation walls are up to seven times stronger than those made of concrete, half as light and three times as elastic. This superior strength and flexibility means that hemp foundations are resistant to stress-induced cracking and breaking, even in earthquake-prone areas. The building material also is self-insulating; resistant to rotting, rodents and insects; and fire proof, waterproof and weather resistant.
Irish builder Henry O’D Thompson of The OldBuilders Company is a fan of using hemp and lime on old stone walls for insulation, condensation, sound muting and breathability. A restoration and conservation specialist who once lived in Canada, he says that lining walls with the hemp/lime mixture makes for a healthy house that doesn’t grow toxic mold.
Pipes can be made out of hempcrete and they, too have greater flexibility and greater elasticity than other those made from conventional materials, and they are resistant to cracking. Stones can also be made out of hemp by wetting the stalk’s cellulose, and forming it into a hard black rock, which can be cut, drilled, cast, carved or formed into any shape.
When hemp hurds are mixed with a combination of lime products, they can produce a light weight insulating plaster, which can be cast around a timber frame or sprayed against a wooden or even stone form. Interior walls can be left exposed or finished with a natural paint. In France, the use of hemp plaster is common, partly because of its high insulation properties but also because it works in old stone buildings.
Steve Allin, a pioneer in the use of hemp as a building material in Ireland and author of the new book Building With Hemp, mixes his own hemp products, which he calls Hemphab, and describes hemp plaster for interior use as having the texture of “sticky muesli”. That, he says, makes it attractive for self-builders who may not have the necessary skills to use the more commonplace plaster. It can also be molded into shapes, textures and finishes.
He cites a social housing project in Suffolk, England as providing a good example of the superiority of hemp as a building material. Suffolk Housing Society built the first two hemp houses in England, as part of an 18-unit social housing development, then studied their performance compared to the regularly constructed buildings. A report was issued in 2002 by the Building Research Establishment (BRE) in regards to the sustainability, economic and environmental differences between the two construction methods. The report’s principal conclusions are that while the hemp homes have far less impact on the environment – they use less energy to build, create less waste and take less fuel to heat – they cost about 10 percent more to build than brick and block houses.
In North America, there are a few hemp houses. In the U.S., the Lakota on the Pine Ridge reservation have constructed a community-based hemp house that was built as a model for sustainable economic redevelopment. The house used hemp and adobe bricks, hemp insulation, and experimented with hemp fiber reinforced cement board.
Another hemp demonstration house, which was much more ambitious in nature, is the rural Ontario, Canada home of Kelly Smith and Greg Herriott, the founders of Hempola, a manufacturer of hemp food and body care products (pictured above). The walls of their spectacular 4,500-square-foot octagonal home north of Toronto are filled with hemp bales in a technique similar to straw bale construction. The floor and ceiling beams of mostly reclaimed wood are stained with hemp oil and the roof is shingled with hemp composite.
With over 120 different projects in the last nine years having used the material in Ireland and over 250 in 16 years in France, this revolutionary but simple material has now come of age. And thus the number of commercially available hemp building products is also increasing. Washington State University has produced hemp fiberboard, which is lighter, twice as strong, and three times as elastic as wood fiberboard, plus it has sound proofing and pressure isolative characteristics absent from wood fiberboard. The process involves chipping the hemp stalk, bonding it together with resins and glues, and clamping it down into molds under high pressure until it hardens.
A company in Chatham, Ontario called Wellington Polymer Technology Inc. is trying to keep up with demand for its maintenance-free Enviroshake brand roofing product, which resembles cedar shakes. Enviroshake is made from hemp, in combination with recycled materials such as post-industrial plastics and crumb rubber from tires.
Hemp is the main ingredient in a French product called Isochanvre. The manufacturer has developed a method of crystallizing the hemp sap and the resulting product has found its way into numerous building products and materials. Isochanvre is mixed with hydraulic lime and water to bind it together, then packed into timber formwork and left to solidify like concrete.
A number of companies are using hemp in insulation products, due to its high thermal resistance, ability to absorb and release moisture, and lack of mold growth, dust and other pollutants. Thermo-Hemp, from Ecological Building Systems in Ireland, is available in both mats and rolls.
England’s Natural Building Technologies, which is a leader in developing sustainable building materials, has a competing product called Isonat, a high-insulation material made from hemp and recycled cotton fibers treated with inorganic salts to provide fire and pest resistance.
Hemp-based paints have even been created and have proved their superior coating and durability characteristics, although the cost of the oil will prevent any mass marketing of them until political climates allows widespread cultivation of hemp One hemp enthusiast has estimated that there are 13 broad categories and upwards of 25,000 specific applications for industrial hemp. Having been used for centuries around the world, it’s certainly poised for a come-back in modern housing construction.
Hemp can be made into any building material, including fiberboard, roofing, flooring, wallboard, caulking, cement, paint, paneling, particleboard, plaster, plywood, reinforced concrete, insulation, insulation panels, spray-on insulation, concrete pipes, bricks, and biodegradable plastic composites which are tougher than steel.
Foundations can be made out of hemp hurds, a processed based on ancient technology adapted for modern use. To do this, set up a plywood frame (preferably hemp plywood), then fill with a mixture of hemp hurd (wood chip-like substance) and combine with lime, sand, plaster, some cement, and enough water to dampen, and let the mixture set for a day. Then take the frame down, but let the mixture continue to harden for about a week. The lime and the hurds create a chemical reaction which binds the mixture together. Amazingly these structures continue to get harder and stronger everyday until they fossilize, as is testament by a 6th century hemp-reinforced bridge in France. After this happens, the hemp foundation walls are as strong as stone.
Hemp foundation walls are 7 times stronger than concrete foundations, half as light, and three times as elastic, which means that these building will bend, but not break. Because of their superior strength and flexibility, hemp foundations are resistant to stress-induced cracking and breaking. Even earthquakes and other natural disaster cannot break or crack these structures.
Hemp foundation homes and buildings are self-insulated, including thermal and sound insulation, resistant to rotting, rodents, insects, and they are fire proof, waterproof, weather resistant, and the walls breath so the rooms do not get stuffy. Hemp homes stay warm in the winter, and cool in the summer.
If hemp were legal in the United States, it would be the cheapest source of raw material for concrete-like foundations. Plus hemp hurds can be processed in existing wood mills without major changes to the equipment. Hemp-foundation homes are ecologically appropriate because they are inexpensive, and can be prepared on site using only a cement mixer, and the material would be cheap and abundant.
Foundation floors can be made in much the same way as the foundation. Hemp resists seepage, and so hemp cement is applicable for pouring onto a soil base to make a foundation floor. The floor insulation hardens into a solid mass which will not shift under pressure.
A German company produces a product called Mehabit, a hemp hurd substance covered with coal-based bitumen, which is sticky, and when leveled out on a hemp cement floor, will dry to form a thermally and phonetically insulated floor.
Washington State University has produced hemp fiberboard is lighter, twice as strong, and three times as elastic as wood fiberboard, plus it has sound proofing and pressure isolative characteristics absent from wood fiberboard. These composites are also resistant to pests, moisture, and funguses.
The process involves chipping the hemp stalk, bonding it together with resins and glues, and clamping it down into molds under high pressure until it hardens.
Concrete pipes can be made out of hemp fiber which cost 1/3 that of polypropylene. These pipes have greater flexibility, greater elasticity, and are resistant to cracking.
Stones can also be made out of hemp by wetting the stalk's cellulose, and forming it into a hard black rock, which can be cut, drilled, cast, carved, or formed into any shape.
Hemp building material could allow us to replace the need for wood, bricks, and fiberglass insulation.
Germany and France are using hemp for construction material, replacing drywall and plywood. A French company has built over 250 homes using hemp materials. Hemp homes have also been built on the Pine Ridge Reservation in South Dakota. Using hemp is economically smart and ecologically appropriate, plus the homes built with hemp are as hard as stone and are not subject to natural disaster. Wow, sounds kind of like a miracle, doesn't it? What are we waiting for?
Hempcrete is a mixture of hemp hurds and lime (possibly including sand, pozzolans or cement) used as a material for construction and insulation. It is easier to work than traditional lime mixes and acts as an insulator and moisture regulator. It lacks the strength and brittleness of cement and consequently does not need expansion joints. It is less dense than concrete and is marketed under names like Hemcrete, Canobiote, Canosmose, and Isochanvre.
Learn more about Hempcrete:
Building with Hemp by Steve Allin Seed Press, 2006, seedpress at eircom.net
Haverhill, Suffolk Hemp Homes Report British Research Establishment, 2002, http://www.bre.co.uk/pdf/hemphomes.pdf