Green to the core

With its sliding sash windows, clean rectangular lines and flat roof, the home that architect Oliver Wolf is building on Chiappini Street in the Bo Kaap, Cape Town, fits right in with the surrounding architecture. A key-differentiating factor is that it is built with industrial hemp.

Even more intriguing is that about half the hemp used in Wolf’s home was grown in South Africa by Rapula Farming near Riebeek-Kasteel, where mature cannabis plants stand up to 3 m high. It is the first home in the country to incorporate locally grown industrial hemp as a building material.

Hemp entrepreneur Tony Budden of Hemporium built South Africa’s first hemp home in 2011. The stylish home in Noordhoek, complete with hemp trimmings like carpets, curtains and sheets made from the natural fibre, is a testament to the possibilities of hemp, one of the oldest cultivated crops in the world.

“The original house showed how a house could be grown,” says Budden. “The walls are comprised of 80% hemp grown in four months. The insulation is hemp; the carpets and curtains are hemp.”

Due to government restrictions on hemp production – it is illegal to cultivate hemp in South Africa outside of on-going trials permitted by government – Budden imported all the hemp for his home from China and France. But now that the trials are nearing completion, Wolf was able to source locally grown hemp for his home.

Hemporium secured four tons of local hemp and six tons of imported hemp for Wolf. The locally grown crop comes from Rapula Farming, Hemporium’s farming partner, and is part of a commercial incubation research trial for hemp – a three-year project now in its last year – permitted by the Department of Health and coordinated by Thandeka Kunene’s House of Hemp.

Hemporium imported the rest of the “shiv” – the chopped up woody core of the hemp plant – from the United Kingdom (UK). It is the waste product from a factory that makes hemp mattresses. Wolf decided to use up the local hemp first and says about 50% of the home will be made from the local product.

He hopes to use the remaining hemp from the UK to build a new green unit at the Yiza Ekhaya Community Project, a community centre in Khayelistha that operates as a crèche, soup kitchen and sewing project with a food garden.

“Hemp is biodegradable and ultimately has a cradle-to-cradle lifecycle,” says Catherine Morris, director of GreenHome, a biodegradable packaging company that is mounting a Thundafund campaign to raise money for the Yiza Ekhaya hemp building. “There’s no doubt that when you’re inside a building made of natural materials it feels like a healthier space to be in.”

“The thing with hemp construction is that it’s one of the easiest ways to lock carbon into a building,” says Wolf. “I wouldn’t like to pretend that this is going to be a carbon-neutral building,” he says, taking into account that a portion of the hemp was imported and the local hemp was processed in Port Elizabeth by the Council for Scientific and Industrial Research (CSIR), adding to the overall carbon footprint. “But it starts to point towards a carbon neutral building.”

Wolf plans to use the home’s ground level, an open-plan studio space with a kitchenette and bathroom, as an office. He will let out the top level, which has two bedrooms.

The secret recipe

The Bo Kaap house has a timber and concret frame that is filled in with hempcrete, a mix of ground up hemp stalks, lime and cement. When dry, the hempcrete has a rough, fibrous texture. Because hemp is used as an infill, the house passed building approval as a timber and concrete structure.

Because of its insulating properties, Wolf will be inserting hempcrete into the gap between the ceiling and floor of the two levels. This hempcrete will be packed so that it is less compact than the walls, so as not to add too much weight.

With hemp, “you’ll end up with a house that is superiorly insulated, compared to a brick house,” says Wolf. “It may cost a little bit more but ultimately you save on the heating and cooling bill.” He says the costs to build are in the R10 000/m² region.

Wolf has a collection of blocks of dried hempcrete stacked in the home’s garage. These represent his experiments to find the perfect hempcrete recipe. For the walls, the trick is to get the right consistency and ensure the hempcrete sets at the right speed while remaining lightweight, he explains.

It is also important to pack the hempcrete manually so that it is not too compressed and maintains its breathability, Wolf says.

Hemp will be used to plaster the interior and exterior walls. The plaster is made from hemp, sand and lime, giving it a natural look. The exterior facades will have a lime render.

Another difference between Budden and Wolf’s home is that Wolf sourced the lime locally too. Wolf notes that unlike other building sites, this one has “a nice smell. The site is easy to clean and has a clean feeling to it, which I believe is all a product of the hemp”.

The full feature appears in the April-May 2015 issue of earthworks magazine.