Details of a naturally finished
interior hemp plaster wall in an Irish cottage by hemp
builder Steve Allin. Photo by Ivan Watkins
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
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
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 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
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.
The McCabe house, built by the Oldbuilders Company and Eco Habitats,
was the first hemp building to be completed in Ireland. Similar to a
standard timber frame house with a mix of hemp and hydraulic lime
structured around the timber, it was finished with a lime rendering
inside and out. The 42-square-meter building is to be used as office
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. 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
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.
Building with Hemp by Steve Allin (Seed Press, 2006)
The Oldbuilders Company (many hemp construction photos)
Rolf Priesnitz is the Publisher of Natural
Life Magazine. He also has over 40 years experience in the
construction industry. This article was published in Natural Life Magazine in 2006.