GBCSA / Green Building / Hemp helps to green buildings

Hemp helps to green buildings

August 27, 2019

It appears that the benefits of growing industrial hemp are too good to ignore.

Besides the fact that it is not marijuana, and so cannot impart any type of high, it absorbs more CO2 per hectare annually than any other commercial crop, including commercial forestry. As a plant restores soil health, as Russian authorities discovered and used it to clean up heavy metals after the nuclear spill in Chernobyl. And it is often grown with no agricultural chemicals due to the dense canopy of shade leaves, which kills off weeds.

Industrial hemp is quickly growing to become a significant industry. Canada was the first Western industrialised country to legalise it, and by regulating it in a manner that resulted in best-practice techniques becoming open-sourced, it has enabled Wall Street to predict that sales for the sector will push past $5-billion a year in the next three years.

Local regulation playing catch-up

Despite South Africa’s ideal climate and lower farming costs, the first step that is needed is for the government to allowed it to be grown commercially, says Tony Budden, a hemp entrepreneur and industrialist.

“At the moment we are slowly using hemp in construction, on a project by project basis through importing. This doesn’t cut it when you’re trying to deliver a competitively-priced material to the building industry and having to bring in containers of hemp from the UK or France pushes the price range into a select niche of eco building.

Tony is hopeful that it will happen sometime in the next year. “There is positive news coming from government and we’re moving in the right direction,” he says.

“Once it can be legally grown on a commercial basis, we will need to determine which standard we will use to process the hemp as there could be variations on how the product binds in South Africa, compared to in Europe. Local supply and standardisation are first needed before it will become a mainstream building material,” he explains.

Building with hemp

Commercial hemp crops often focus on the oils and textile materials produces, and the building material – found in extremely high silica-content of the woody stem – is a by-product, notes Josh Swart, Co-Founder of OGCT.

Besides locking in the significant amount of carbon it absorbed while growing, using hemp means you are not mining for your building material, at scale the required amount of hemp can be grown relatively close to the construction site within four months.

The hemp stems are ground up into sawdust and mixed with lime. This hempcrete can be used to create a concrete-type mixture or bricks. Often the slurry is poured into a wall form, or around timber or steel posts. It then hardens into a thick permeable concrete-like wall characterised by excellent insulation properties.

Interestingly the hempcrete continues to absorb carbon from the air, calcifying as it does so. This ongoing calcification makes the walls stronger, Josh says.

Hemp: a young, but fast-moving industry

Beyond hempcrete, the various materials produced by the hemp plant are incredibly versatile, as Tony Budden demonstrated when he set a local president by using it in 2011 to build and furnish his home in Noordhoek, Cape Town. The insulation, cupboards, flooring and wall panelling were all hemp.

“New advances using hemp as a building material continue to be made. A company in the US recently developed a timber frame structure out of hemp wood which is yielding stronger results than a Redwood tree. And remember that it takes the hemp just months to grow, not decades,” notes Josh.

Hemp has been used since ancient times, although when it was outlawed it was replaced by plastic, cotton, fossil fuels and other big-industry products. Today as we understand the harmful impact of these industries, many markets are returning to hemp as a viable sustainable alternative.

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