Building Green

"It smells like comfort."
"It smells a little like lime. We're using the stock. You cannot smell cannabis -- it has nothing to do with smoking weed or cannabis plants."
"It's an industrial agriculture crop."
Sergiy Kovalenkov, 33, Ukrainian civil engineer

A self-built hempcrete house, combining timber cladding and lime render finishes.   The Last Straw

Industrial hemp contains a minuscule 0.3 percent of tetrahydrocannabinol (THC), the substance linked to the effect of smoking marijuana to get high. In comparison, cannabis contains up to 20 percent of THC. Cannabis plants produce hemp which since ancient times has been recognized as a useful material for a multitude of purposes, for not only do the fibers produce strong rope, and clothing, but used in combination with lime it makes for an enduring building material.

In sixth-century Gaul (now France), a bridge was constructed with hemp mortar, a sustainable building material felt to be more reliably durable than concrete or steel. Hemp's woody fibers combined with lime produce a natural, light concrete with thermal mass that is insulating to a high degree. Hemp mortar does not attract pests, nor mould. It has sound acoustics, results in low humidity and no pesticide is required to grow the plant.

It takes four months for the plant to mature from seed to harvest time. It is not yet considered a useful crop for building purposes in North America, but that is set to change as botanists and builders begin increasingly to evince interest in its qualities. In the United States less than 4,000 hectares is devoted to hemp. That crop is deemed sufficient to build five thousand single-family homes with.

Green Building Materials, Canada

In Canada double the arable land as opposed to the U.S. is devoted to producing hemp. Spain, Austria, Russia and Australia are now seeing an increased interest in growing hemp, among the 30 nations that now produce it. In China's Yunnan province no fewer than ten thousand farmers devote their agricultural holdings to growing hemp. In 1980s Europe cultivation of hemp was rediscovered.

The largest hemp producer in the European Union is France. The growing appreciation of its properties as a sustainable-yield construction crop has resulted in hundreds of buildings across Europe using hemp as insulation between walls and roofs, and under floors in wood-framed buildings. Cannabis sativa, ubiquitously grown, flourishes in a variety of climates where it can grow as tall as five meters and close to three centimeters in diameter.

Rope, sails and paper are sourced from the tough fibre of the plant's tough layer. The inner layer, the pith, is surrounded by the woody core, called the hurd which produces the tough fiber.  To address an absence of international standards related to building with hemp, ASTM International, a technical standards organization, set out in 2017 to form a committee that would perform that function.



The Hemp Industries Association estimated the retail market for hempcrete in 2014 at $573-million in the United States. Roughly fifty hemp homes have been built in the United States and in Israel its first hemp house was built on the slopes of Mount Carmel. Israel, as it happens, is in the forefront of studying and experimental research of cannabis. Hemp ventures have risen in Nepal and Ukraine.

It is considered by manufacturers to be ideal for low-rise construction, attractively stucco-like in appearance and toxin-free. Those who promote it emphasize its reduced carbon footprint with its lower requirement of heat in its creation than standard limestone concrete. Typically planted in March and May in northern climes or between September and November below the Equator, plants are cut by hand then left to dry for several days before being bundled and placed in vats of water, swelling the stalks.

The block-like bricks produced by blending dried fibers with lime have a variety of uses, the product known as hempcrete. What its promoters are concerned with at this juncture is the normalization of recognizing the plant for its utilitarian purposes and legalizing it as an agricultural-building crop, separate and apart from its other, more acknowledged and familiar purposes as a narcotic agent. In the U.S. that meant taking it out of the Controlled Substances Act.

In Britain, HAB Housing built five homes last year with hempcrete, while Just-BioFiber in Canada completed a house with an interlocking internal framed hemp-block on Vancouver Island. In New Zealand 500 bales of Dutch hemp constructed a property that sold for $650,000. A four-meter hempcrete wall can produce 15-degree Celsius year-round temperatures absent heating or cooling systems.

"The overall environmental footprint is dramatically lower than traditional construction", noted Joy Beckerman, a hemp law specialist and vice-president of the Hemp Industries Association.

New build hempcrete housing in Swindon, UK (built by Haboakus)  The Last Straw