January 23, 2010 – Bath,U.K. – The director of the UK’S Building Research Establishment Centre for Innovative Construction Materials at the University of Bath recently started a £740,000 project, funded by the UK government and the construction industry, to study and develop the material’s use in building. The research builds on foundations laid more than a thousand years ago. Archaeologists in France have discovered a sixth-century bridge where the stones are held together with hemp mortar.

Cultivated for thousands of years for its fibres, which are used to make ropes and textiles, hemp, otherwise known as Cannabis sativa, was so important to the economy during King Henry VIII’s reign that farmers had to grow at least a quarter of an acre or risk a fine. In the latter decades of the 20th century production slumped as cotton cloth and man-made fabrics became prominent but in the 21st century hemp’s reputation is being rebuilt, partly thanks to properties that make it an ideal building fabric for homes.

From bedding to building

The inner woody core of the hemp plant, the “waste” by-product of fibre extraction, is used in construction. Until recently the most common use for these stalks, also known as “shiv”, was as horse bedding.

In effect, the hemp replaces the aggregate – stones and pebbles – that are usually mixed with cement to form concrete. (One of the leading companies involved in hemp building, Lime Technology, calls its product “hemcrete”.)

By varying the quantities of shiv to lime, different preparations can be made that are either cast or sprayed into a frame or formed into structural blocks. Curved walls can be formed as, being a fairly dry material, the hemp/lime mix can be shaped in lightweight, flexible shuttering.

The hardened, finished material, which looks a little like baked mud full of flecks of straw, can be rendered with a layer of lime plaster or left untreated for a rustic look.

Today, industrial hemp (a strain of cannabis that has almost no narcotic quality) is being processed into an environmentally friendly construction material that is then mixed with a lime binder to make a material that can be poured and cast like concrete or formed into bricks.

Hemp’s environmental credentials are many: it needs little or no pesticide or herbicide to grow. Its impact on food production is mitigated by the fact that it is the second-fastest growing agricultural crop in the world (after bamboo), maturing from seed to harvest in four months. Therefore, food crops can still be cultivated for two-thirds of the year and they will have the advantage of growing in soil that has been improved by hemp’s nutrient-enhancing actions.

Hemp does not take up much surface area – one hectare provides enough material to build one house. “All the 180,000 new-build homes the UK government ambitiously estimates are needed each year could be built with hemp grown on just 1 per cent of Britain’s agricultural land,” says Walker. (Last year, 5,000 hectares were grown in the UK – mostly for the fibre, which is used in the car industry.) Of course, hemp could also be used in the renovation of the millions of empty houses in the world. In terms of carbon emissions, hemp certainly trumps ubiquitous cement and concrete, the production of which causes between 5 and 10 per cent of global carbon emissions, says Walker.

Indeed, hemp construction can, theoretically, result in a building with zero carbon emissions or one that contributes to the eco-crusade by storing carbon dioxide. The plant – like all plants – absorbs the gas during its growth. Walker estimates that a square metre of a 300mm-thick hemp/lime wall stores about 33kg of carbon dioxide. By contrast, the manufacture of the materials that go into a square metre of standard cavity masonry wall is responsible for 100kg of emissions.

As global concern about carbon emissions leads governments to legislate for low carbon housing (the UK aims for all new-builds to be zero carbon by 2016), hemp’s use in construction is growing.

In France, where its revival began a few decades ago, there are several thousand hemp houses. In the UK, over the past two years a few hundred properties have been built, including a 4,400 sq metre warehouse with a living roof for the Adnams brewery in Suffolk, eastern England. Constructed from 90,000 hemp/lime blocks with hemp/lime cavity insulation, all made from locally sourced crops, it is the largest hemp building in the world.

The company estimates that there is the equivalent of 100-150 tonnes of carbon dioxide locked up within its walls while a conventional brick building of the same size would have been responsible for about 300 to 600 tonnes of CO2 emissions.

As well as the possibility of being carbon negative in construction, hemp has many characteristics that mean buildings will have low – or zero – emissions during use. Unlike most lightweight building materials, such as wood, it has a high thermal mass, meaning that it stores heat from the sun and releases it slowly during the cool of the night.

It is also breathable while being airtight, is good for soundproofing and is hygroscopic, meaning it moderates humidity. No wonder that Walker boasts that hemp provides “one of the most credible and novel uses of renewable crop materials in construction. It offers benefits for the agriculture and construction industries, occupant health and for wider society through the delivery of lower carbon buildings.”

Its proponents are keen to point out that hemp/lime is ideally suitable for domestic uses too. “You can build a very conventional house with it,” says Ian Pritchett, chairman of building products company Lime Technology. “It doesn’t have to look wacky.” He shows me round a very pleasant but ordinary-looking demonstration house the company has built in Watford, north of London, at the Building Research Establishment. Significantly, the company has changed its name from The Hemp House to The Renewable House.

Pritchett denies that this is to avoid some of the negative connotations people still associate with the cannabis plant. “The name-change reflects the nature of some of the other materials used in construction – mostly sustainably harvested natural products such as Scandinavian pine and sheep’s wool.” The three-bedroom house, which took just 15 weeks to build and cost £75,000, has exterior walls that have been smoothly rendered and painted. You would never guess that they are constructed from a plant most commonly associated in the public mind with a kind of joint not found in a building skills manual.

The house has so impressed the UK government that in November last year the Department of Energy and Climate Change, in partnership with the Homes and Communities Agency, announced that £5m of grant funding would be available for developers that build affordable homes from renewable materials such as hemp. After years of being associated with a hippy ethos and despite the potential for jokes, it appears that there is now good reason to take Cannabis sativa seriously. By Paul Miles. Source.

November 22, 2009 – Leave it to Asheville N.C. to be the first place in the country to build not just one, but two houses largely out of hemp.

Well-established as a green building center, Asheville has two homes under construction – one in West Asheville, another off Town Mountain Road – that use hemp as a building material. The builders and Greg Flavall, the co-founder of Hemp Technologies, the Asheville company supplying the building material, maintain that they’re the first permitted hemp homes in the country.

“This area is known to walk the talk of being green,” Flavall said, adding that the Asheville area has by far the largest percentage of Leadership in Energy and Environmental Design, or LEED, builders of anywhere in the country. Hemp is derived from the same plant that marijuana comes from. Although it contains very little of the active ingredient that gets people high and is completely impractical to smoke, it’s still illegal to grow it domestically.

But builders can import industrial hemp products like Tradical Hemcrete, the material Hemp Technologies sells. When mixed with water and lime, it makes remarkably strong, resilient walls. Some builders generically refer to the walls as hempcrete.

Clarke Snell, of the Nauhaus Group, a collaborative of local companies building the West Asheville home at 67 Talmadge St., describes the resulting structures as “forever” walls. Should you take a wall down, the hemp inside is also reusable.

“Basically, the only thing that can tear this wall down is water,” Snell said, adding that it would have to be a steady stream.

Flavall said the last study done in Europe puts the life span of hemp walls at 700-800 years.

“And even at the end of that, you can use it as fertilizer on a field,” he said.

How it works

The hempcrete mixture starts with 55-pound bales of Tradical Hemcrete brand hemp shiv, or ground-up hemp plant stalks. Workers mix it into a standard concrete mixer, four parts hemp, one part lime and one part water. They pour the resulting slurry into small containers and then pack it between plastic forms that raise a wall two feet at a time. The walls are built around standard stick-built framing.

It takes about a day for a wall to dry and about two weeks before it’s ready for exterior or interior coatings of lime stucco or plaster. Even with those coatings, the material still breathes.

“One of the main reasons I was drawn to the lime and hemp mixture is the breathability – there’s no mold, no mildew,” said Anthony Brenner, whose company, Push Interior/Architectural Design + BuildTechnologies, is building the Town Mountain home. “The lime is constantly taking in carbon, so it’s carbon-negative.”

Hempcrete is also a natural deterrent to insects, and it’s extremely fire-resistant, mainly because of the high lime content. It takes about 2 acres worth of hemp to do one house.

Cost calculations

Hempcrete is more expensive upfront than traditional building materials, mainly because of the shipping costs. Flavall says his company has to import it from Europe, which about doubles the cost.

For the Town Mountain home, he’ll use about 1,875 cubic feet of hempcrete, at a total cost of about $56,250.

That’s higher than typical construction, but Flavall says you’ll net a 30-40 percent reduction in framing costs because less lumber is needed. You also have the potential for a lighter foundation because the hempcrete walls are lighter. Also, homeowners may be eligible for a 10 percent reduction in insurance rates because the product is so flame-retardant.

Nauhaus partner Chris Cashman points out another major advantage: “With this, it’s your Sheetrock, insulation and Tyvek (moisture barrier) all rolled into one.”

Calculating the cost of a Hempcrete home gets complicated.

“We think we can build a house like our prototype for anywhere from parity for a high-end custom home – think Biltmore Village – to 5-15 percent more for a typical home,” Snell said. “However, that’s not the point because construction cost is not your monthly cost.”

He points out that a typical homeowner’s monthly home costs include the bank mortgage, utilities, maintenance, insurance and more. If you’re building a house that uses 15 percent of the energy of a conventional home, then you can take money saved on utilities and put it into construction and end up with the same monthly cost.

“Our mission is to provide carbon-neutral housing for the same monthly cost as a typical home,” Snell said.

Tim Callahan, another of the Nauhaus partners, puts it this way: “The reason it begins to be affordable is because we’ve reduced the energy loads so much.”

The costs over the long haul should appeal to the green-minded.

“The bottom line of this and a traditional house is it’s about cost-neutral,” Brenner said.

Labor-wise, it’s quicker to put up the hemp and plaster than all those other materials like Sheetrock and insulation. Brenner said it will take them about a week to get all the hemp walls up. The Nauhaus guys have put up a test wall and are waiting on the plastic forms from Brenner to do all their walls.

Model efficiency

The house Brenner is building will have 12-inch thick walls, while the house on Talmadge Street will boast 16-inch thick walls and will be 80 percent more efficient than code requirements – so efficient that Snell claims it could be heated solely by the body heat of 18 people.

Besides hemp walls, the 1,450-square-foot, four-bedroom house will have solar panels on the roof to generate enough electricity to power the home, with a surplus. It will have an earthen exterior made from the soil on site, rainwater gathered from the roof and a mostly edible landscape.

The home will be a prototype that the Nauhaus group will use for tours and education.

The house will be owned by the Nauhaus Group itself, although chief engineer Jeff Buscher and his family will live it for two years before it’s sold to allow for energy-efficiency analysis and other research.

Brenner is building the 3,100-square-foot Town Mountain home for Russ Martin, a former Asheville mayor and retired stockbroker, and his wife, Karen Corp. “We’re not afraid of trying something new,” Martin said. “We’ve always been adventurous that way, and this looks like it’s going to work out really well.”

Snell stressed that getting the Nauhaus going has involved a massive, collaborative effort involving multiple local companies.

Based in Asheville, the project is led by Think Green Building, Eco Concepts Development, Eco Concepts Realty and Green Plan.

Both Brenner and the Nauhaus partners want to expand hemp building far and wide.

Brenner said he’s working on a commercial project in Maggie Valley and another home in the Leicester area.

And they’d love to see farmers have a chance to grow hemp legally.

“Our feeling is: What a great crop this would be for North Carolina’s tobacco growers to get into,” said Callahan, the Nauhaus partner. “Bringing this in from England is probably not the greatest idea (economically). If local farmers can benefit from this, it would be great for them and great for the economy.”

Still, as Snell puts it, right now “what you have is a product that you can’t grow but you can buy” in the United States.

Brenner thinks the technology will take off when potential homeowners and developers come to understand its advantages.

“We’ve been seeing interest from all over the country,” Brenner said.

“People are truly interested in green construction and green building, and I don’t know how much more green you can get than this.”

Flavall said another hemp house will start up next year in Franklin, and he’s receiving strong interest in other projects.

“I’m seriously of the belief that we’re making history here,” he said.

By John Boyle Source. On the Net: