U.S. hemp-based construction advances with fire-safety tests, new book

By Jean Lotus
U.S. hemp-based construction advances with fire-safety tests, new book
European buildings have used hemp-and-lime construction for decades, like in this multi-story Italian apartment building. Photo courtesy of Jonsara Ruth

DENVER, May 7 (UPI) -- Natural materials builders seeking to grow a market for industrial hemp in the United States are moving forward after successful testing for building safety codes and recognition by a national architecture and design program at a U.S. university.

Hemp advocates have identified lime-hemp building material, called "hempcrete," as an opportunity to build a market for hemp grown for fiber. Challenges have been a lack of supply, building code regulations and a lack of education among architects and designers, builders say.


Hemp advocates are encouraged by building safety tests that are moving forward faster than expected, said Dion Markgraaff, vice president of the recently formed U.S. Hemp Building Association, based in Denver.

Already this spring, hempcrete passed fire safety tests under the jurisdiction of ASTM International, formerly known as the American Society for Testing and Materials. Hempcrete was deemed inflammable in smoke development and flame-spreading tests.

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The building association plans to apply soon for certification from the International Code Council, where engineers would to determine the technical standards and mix ratios to include hempcrete as a permissible building material in the United States.

"They're excited to help us get this done," Markgraaff said. "We thought it would take years, but it's moving very quickly."

Hemp construction products have the potential to generate jobs and economic growth on a local level, he said.

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"Farmers can grow hemp locally. Lime is everywhere, water's everywhere. This building material can boost the local economy and have a smaller [carbon] footprint," Markgraaff said.

Chipped hemp bark, lime binder and water are mixed together to make hempcrete. The material dries to a strong, stone-like substance that is fireproof, mold-proof and insect-proof, researchers at New York's Parsons School of Design's Healthy Materials Lab said.

Hempcrete has been used in building construction for 30 years in Europe, replacing siding, insulation and drywall, but fewer than 50 hempcrete structures have been built in the United States.

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A forthcoming 200-page book, "Hemp + Lime: Examining the Feasibility of Building with Hemp and Lime," edited by architect Alison Mears and Jonsara Ruth, an associate professor of design, presents an overview of a five-year research project on hemp-lime construction as a natural material for affordable housing.


For the book, researchers studied international uses of hempcrete and toured multi-story apartment buildings made of hempcrete in Italy and other European countries.

"Hemp is a unique plant because the silica inside its stalk allows it to attach to and bind with lime really well," Ruth said.

The hemp plant's cellulose can absorb large amounts of atmospheric carbon dioxide while growing. When made into hempcrete, 9- to 12-inch-thick walls also are breathable and temperature controlling, unlike air-tight traditional building materials that trap off-gases from petroleum-based products, paints and solvents, Ruth said.

Builders and researchers envision hemp building materials in the construction supply chain, available off the shelf for builders.

They have had some successes.

Hempcrete made into pre-formed blocks is lighter in weight than traditional masonry material like brick or stone.

"These union masonry workers don't have to break their backs working with hempcrete blocks," Ruth said.

Another example is "HempWool" insulation batts, imported from Canada, which use industrial hemp fiber instead of fiberglass and can be installed with bare hands.

"With every other insulation material, you have to wear hazmat suits with a full respirator and gloves." said Tommy Gibbons, co-founder of Sun Valley, Idaho,-based Hempitecture.

"Hemp is the material that the green building industry has been waiting for," said Vermont-based architect Bob Escher, president of the hemp-building association.


"There are so many materials we'll be able to make out of hemp in the next 50 years," Escher said. "It will really change the whole construction industry in my mind."

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