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Project

Hemp House Breathes Easier in Carolina

Credits: ©2011 Push Design

There are an estimated 25,000 different uses for hemp, including sports cars, clothes, and biofuels. Since the 1960s, it’s been used in Europe and Australia as a building material, too. In 2010, the first hemp house was built in North America in Asheville, North Carolina using a product called Hemcrete from the UK. It is a breathable, natural and toxin-free system with an R-value of 2.4 per inch, and the material even helps filter the air for improved indoor air quality. One house built with hemp is estimated to be equivalent to ten acres of trees in terms of the carbon sequestered, therefore achieving better-than-zero carbon footprint. Hemcrete is a blend of a lime-based binder and the woody core of the hemp plant (known as shiv) that produces highly thermally efficient walls. The home is 3,000 square feet plus a garage, with 12-inch thick walls, Energy Star appliances, dual-flush toilets, high-performance windows and LED lights. (Scroll to bottom for additional resources)

 

Hemcrete Standard Wall Section

Standard wall section for Hemcrete. ©2011 Tradical Hemcrete

Hemp Homes Are Cutting Edge of Green Building
By Wendy Koch, USA TODAY
Hemp is turning a new leaf. The plant fiber, used to make the sails that took Christopher Columbus' ships to the New World, is now a building material.

In Asheville, N.C., a home built with thick hemp walls was completed this summer and two more are in the works.

Dozens of hemp homes have been built in Europe in the past two decades, but they're new to the United States, says David Madera, co-founder of Hemp Technologies, a company that supplied the mixture of ground-up hemp stalks, lime and water.

The industrial hemp is imported because it cannot be grown legally in this country — it comes from the same plant as marijuana.

Its new use reflects an increasing effort to make U.S. homes not only energy-efficient but also healthier. Madera and other proponents say hemp-filled walls are non-toxic, mildew-resistant, pest-free and flame-resistant.

"There is a growing interest in less toxic building materials, says Peter Ashley, director of the U.S. Department of Housing and Urban Development's Office of Healthy Homes and Lead Hazard Control.

"The potential health benefits are significant," he says, citing a recent study of a Seattle public housing complex that saw residents' health improve after their homes got a green makeover.

The U.S. government has not taken a "systemic approach" to studying chemicals in homes and instead addresses problems such as asbestos, lead, arsenic and formaldehyde only after people get sick, says Rebecca Morley, executive director of the National Center for Healthy Housing, a private research group.

She says green building so far has focused mostly on the environment, not the health of the people inside.

Ashley agrees that federal attention has been "sporadic," but says an interagency group began meeting last year to tackle the issue more broadly. He says HUD is funding more research on the health and environmental benefits of eco-friendly homes.

Some green-rating programs, such as the one run by the private U.S. Green Building Council, give points for indoor air quality.

"We are taking the next step in green building," says Anthony Brenner, a home designer with Push Design who created Asheville's first hemp home. "We're trying to develop a system that's more health-based."

Brenner says he's been searching for non-toxic materials because he wants to build a home for his 9-year-old daughter, Bailey, who has a rare genetic disorder that makes her extremely sensitive to chemicals. "We have to keep her away from anything synthetic," he says, or she'll have seizures.

He says a hemp home can be affordable, even though importing hemp makes it more expensive than other building materials, because skilled labor is unnecessary and hemp is so strong that less lumber is needed.

The hemp mixture — typically four parts ground-up hemp to one part lime and one part water — is placed inside 2-foot-by-4-foot wall forms. Once it sets, the forms are removed. Although it hardens to a concrete-like form, wood framing is used for structural support.

"This is like a living, breathing wall," Madera says.

Hemp absorbs carbon dioxide and puts nitrogen into the soil, so it's good for the environment, he says.

Alex Wilson, executive editor of Environmental Building News, says hemp can be grown with minimal use of chemicals and water. He says it has a midlevel insulating value (R-2 per inch) but is usually installed in a thick enough wall system to make it appropriate for all but the most severe climates.

The mixture, "Tradical Hemcrete," has not previously been used in U.S. homes, but in 2008 it went into a community center on the Pine Ridge Reservation in Badlands, S.D., as well as a small chapel and pottery studio near Houston, says Mario Machnicki, managing director of American Lime Technology, a Chicago company that imports hemp from the United Kingdom.

Asheville's second hemp home will be finished in about six weeks, says builder Clarke Snell of the Nauhaus Institute, a non-profit group of designers, engineers, developers and others interested in sustainable urban living.

Snell says the home, which has 16-inch-thick walls, is airtight and energy-efficient. He expects it to meet rigorous Passive House Institute standards, which call for homes to use up to 90% less energy than regular ones.

"On the coldest day in winter, the body heat of 10 people should heat the home," he says. "We're basically building a European home."

Snell says his group will own the 1,750-square-foot house, and its engineer will live there for a couple of years to monitor energy use.

He doesn't know how much it will cost because, as a prototype, it was built with donations and volunteer labor.

The owners of the first hemp home say it cost $133 a square foot to build, not including land and excavation.

"That's pretty remarkable" for a custom home in Asheville, which is a pricey area, says Karon Korp, a writer who moved into the house in July.

Korp says she and her husband, Russ Martin wanted primarily an energy-efficient home.

They're not particularly sensitive to chemicals, but they were drawn to Brenner because of his modern aesthetic and green building enthusiasm. She says they're thrilled their house is made of a renewable, toxic-free material and hope it sets an example for the nation.

"Hemp could replace tobacco if it were legalized," says Martin, Asheville's GOP mayor from 1993 to 1997. He says some area tobacco farms have gone bust.

Martin says they have spent less than $100 a month so far to cool the home, which has 3,000 square feet plus a garage. It has 12" thick walls, Energy Star appliances, dual-flush toilets, high-performance windows and LED lights. Korp says they might add a windmill, because the house sits atop a mountain.

They say they have fantastic views. "We seen the sun rise," he says. She adds, "and the sun set."

The following article is from Building Green.com
Hemcrete – A Hemp-Lime Composite Insulation for Walls
September 2010, by Alex Wilson
Tradical® Hemcrete® is a non-structural, rigid, insulating, composite wall fill comprised (by weight) of about 38 percent hemp and 62 percent lime-based binder. The Tradical lime binder is manufactured in the U.K. by Lime Technology, Ltd., under license from multinational Lhoist Group, headquartered in Belgium with lime operations worldwide.

I first learned about Hemcrete at the Build Well Symposium in San Francisco January 2010. Mario Machnicki of American Lime Technology in Chicago, the U.S. distributor of the Tradical Hemcrete wall system. To date, four to five houses have been built in the U.S. using Hemcrete, including a just-completed house in Asheville, North Carolina, that has been widely publicized.

The industrial hemp used in Hemcrete (the same species as marijuana, but with far less of the narcotic THC) is currently sourced from England, where it can be grown legally, but Tom Glab of American Lime Technology told me that they are working to find a source in Canada, where industrial hemp is also legal.

Federal law in the U.S. currently prohibits the cultivation of industrial hemp--though in the past it was widely grown for many uses, including paper, rope, and textiles. In fact, hemp sails carried Columbus's ships to the New World, founding fathers George Washington and Thomas Jefferson grew hemp, and until the late 1800s three-quarters of the world's paper was made from hemp, as were most fabrics until the 1820s with the invention of the cotton gin.

Hemp proponents point out that the plant can be grown with very low environmental impacts--little fertilizer or pesticides being needed--and that a building system based on hemp sequesters carbon very effectively. One acre of help produces 4.1 times as much fiber as the same acre of trees, according to Hemp Technologies, LLC, and the plant removes carbon from the atmosphere four times as efficiently as trees.

To make Hemcrete, the dried stems of hemp, referred to as "shiv," are mixed with the lime-based binder. Moistened, the mix is placed into wall forms--typically spaced to achieve a 12-inch-thick wall--which can be removed the next day. While the material hardens to a rigid, concrete-like form (I have a large sample from American Lime Technology sitting on my desk, and it seems very strong), it is considered non-structural. Wood or steel framing members are used in the wall system to provide structural support.

After removing the forms, two layers of lime stucco are applied on the exterior, a base coat and a finish coat. The interior side is finished with lime plaster. With the lime stucco and plaster, the entire wall system is breathable.

In the U.K., Hemcrete is also sprayed into an open cavity, using Gunite or shotcrete technology, against a single form that remains in place, but to-date, only poured applications have been done in North America.

As for thermal performance, Hemcrete insulates to about R-2.3 per inch, according to Tom Glab, so a typical 12-inch-thick wall provides about R-28. This is a reasonable R-value in moderate climates where use of the material is being most actively pursued. The monolithic wall system also provides effective thermal mass--like adobe or autoclaved aerated concrete--which can be beneficial in climates with a lot of sun and large diurnal temperature swings (such as the Mountain states and Southwest).

Cost depends on the purchase volume--due (today) to the costs of shipping from the U.K. When ordered by the 40-foot container load, a 22 kg (49 lb) bag of binder costs about $30 and a 20 kg (44 lb) bag (bale) of hemp shiv costs $28. Including the base and finish stuccos, Glab said the materials cost for a 12-inch wall are about $19/sq ft. American Lime Technology is hoping to source the materials closer to home: "The idea is to be green, so we want to avoid transportation from England," Glab told me.

One of the first completed houses in the U.S. using Hemcrete was designed and built by Anthony Brenner of Push Design, in Asheville, North Carolina. The 3,400 sq ft home is owned by a past mayor of Asheville, Russ Martin, and his wife. Completed this summer, the "Push House" features a wide range of green features besides the Hemcrete walls. Total construction cost of the house, according to a recent CNN news report was $133 per sq ft.


Documents

  Guide to Use of Lime in Historic Buildings (5,329 kb)


Resources

Hemp Powered

House Made of Hemp CNN Video Link

Tradical Hemcrete

Hemp Building


Videos

Watch Hemcrete at BRE UK Thumbnail

Hemcrete at BRE UK Video

Watch Hemp House Thumbnail

Hemp House Video

Watch Hemcrete Thumbnail

Hemcrete Video

Watch Hemp and Lime Construction at WISE Thumbnail

Hemp and Lime Construction at WISE Video