Seven years ago, on her birthday, Gill Staniland attended a TEDx conference, themed ‘Be Water My Friend’. There she heard Tony Budden, co-founder of Cape Town-based business Hemporium, speak about the industrial uses of hemp. Ever since then, Staniland has believed it makes sense to build with this ancient and natural material.
‘The idea is to retire to the countryside. I’m an IT consultant and I’ve spent most of my life under fluorescent lights, but always longed to be outside,’ she says. ‘To me, the question was not, “Why hemp?” but rather, “Why not hemp?”.’
A few years after the conference, she volunteered at the Yiza Ekhaya soup kitchen build, a hemp project by Wolf and Wolf Architects. She made a promise to architect Oliver Wolf to call him about her proposed house.
‘A lot of people say they will call me after these workshops, but a few months later, when she had found her site, [on a 7 ha plot at Baardskeerdersbos in the Overberg] Gill made good on her promise,’ says Wolf.
The brief was for a residential house that was sustainable but also modern. ‘I wanted something that demonstrated comfort and style, but was tuned into the environment,’ says Staniland. ‘I asked for a small space, but with the vision of maybe expanding later, and I wanted to be able to connect with the outside world and maximise the views.’
Wolf responded with a simple floor plan for a 57 m2 dwelling. The services were aligned along the back wall of the living space and a transparent north facade balances thermal comfort with an orientation that capitalises on the views over the valley.
Consistent with the concept of simplifying the services, Wolf designed a butterfly roof with a central box gutter for rainwater harvesting. Half the roof is oriented towards the north and angled to optimise the collection of solar energy. Sewage is treated on-site with a Little Green Monster biogas digester, which is a simple, entry-level unit. ‘It’s more of a glorified septic tank, where it burns off the gas to break the methane down into carbon dioxide and lower the global warming potential,’ says Wolf.
‘The cooker flame is a little pongy and only produces a low heat suitable for slow-cooking. We provided an open-air cooking facility and scullery facility for slow-cooking. The gas is perfect for this set up.’ To make it functional for general cooking applications or for use in a gas geyser, secondary technology can be added to improve functionality, he explains.
The establishment of the site, along with the sustainable services took a staged approach. ‘The first thing we did was install a shipping container for storage and drop an 85m borehole, so that we had water for construction. The borehole pump is run by three solar panels on the roof of the container and pumped uphill to a tank behind the house. The position of the tank allowed for gravity supply of water to the construction site,’ says Staniland.
Hemp appeared in widespread production about 3 000 to 4 000 years ago in Europe and China, and evidence suggests that it was cultivated as far back as 10 000 years ago. By biblical times, uses for its fibre were renowned and it was a fabric of choice in apparel and home furnishings. It is the strongest natural fibre known to humankind and competes well with nylon. Of the natural fibres, it is resistant to water decay and so made excellent ropes and sails.
The part of the plant used as a construction material is called shiv, or hurds. It is a by-product of hemp fibre production, the woody core of the hemp stalk, and is chipped to provide a cellulose aggregate in a lime casting (hempcrete) or to manufacture boards and panels. There are a number of possible hempcrete mixes that can incorporate cement or ground granulated blast slag in the mix.
Budden, hemp supplier on the project, explains: ‘The hemp has an open pore structure that absorbs the lime. As the hemp breaks down, the carbon bonds with the lime to form calcium carbonate and it cures into a harder state over time’.
On Staniland’s project, Wolf decided to forgo the cement content and used a mix of 100% lime. The construction of hempcrete uses relatively standard shutter and tamp techniques to cast the walls, but Staniland struggled to find a contractor who was willing to work with hempcrete. ‘The contractors were unfamiliar with the technology, and most of them over-quoted,’ she says. ‘Eventually I decided to build the walls myself.’
The foundations and service sleeves were installed by local contractors and Wolf appointed a team to erect the timber frame and structural elements that had been manufactured in his factory in Cape Town. ‘This provided protection from the elements so Gill could build the infill walls in her own time.’ After this, Staniland hosted a series of hempcrete build workshops for the installation of the walls and Geoplast came on board with a prefabricated shuttering system. ‘It was very useful in constructing the hempcrete walls as it sped up the process of recreting and moving the shuttering, which was definitely easier than making up plywood shuttering,’ says Wolf.
Hempcrete infill performs well in a number of ways. It provides strength to timber stud walls and outperforms traditional cross-bracing against lateral forces. In addition, it provides excellent thermal and acoustic performance, depending on the density of the hempcrete. The thermal comfort of the interior is improved by the moisture buffering properties of hempcrete.
Like other cellulose-based materials, it has the ability to moderate the fluctuation of the relative humidity of an enclosed space through the adsorption and desorption of moisture in the air. According to 2015 research by Latif, Lawrence, Shea and Walker into the efficacy of hempcrete’s moisture buffering, leaving the walls exposed, or painting them with a clay or lime-based finish, provides better moisture buffering performance than when finished with trade paints.
A typical mix suggested by Tom Woolley of Rachel Bevan Architects indicates one part hemp hurds to two parts lime. Hemp has very low embodied energy, is a rapidly renewable material, biodegradable and, when used as a building material, offers carbon sequestration opportunities. According to a life cycle assessment in the Journal of Cleaner Production, the carbonation process of lime combined with the CO2 absorbed during the growth period of the hemp, means that, locally produced hempcrete has a negative carbon rating and can produce a building with a net zero carbon rating.
Hemporium’s farming partner, Rapula Farms, has been researching the commercial production potential of hemp and has concluded phase one of production under a commercial incubation research trial. On the basis of this, and reports from other sites, the Department of Agriculture, Forestry and Fisheries, with the National Agricultural Marketing Council, is making recommendations for the expansion of the project with the aim of testing production at scale and proving commercial viability.
‘Once the seeds are in the ground, harvest is reached within four months and finished product can be on the market within a year,’ says Wolf. He holds up an imported sample of board that has the heaviness of shutterboard, but the surface appearance of oriented strand board. ‘This is an Italian product that was on the market within a year of legalisation of hemp production,’ he says, nodding to the potential that SA could bring boards to the market in similar timelines. Considering the existing infrastructure for paper production and board manufacturing, the legalisation of hemp production in the country could be a major boon for both the economy and the green building industry.
Since its early cultivation, the number of uses for hemp has multiplied as scientists continuously unlock new products and innovative applications. Thanks to this versatile plant, you can now grow your own house.