In detail: the nautilus shape is ergonomically sound

Using earth to build a house is a cheap and environmentally sound way of getting the job done, says the owner of Joburg’s first earth house.

IT looks a little like a giant anthill, and involves the same ingenuity that thousands of ants put into making their homes. But this home is for humans and it has been growing steadily over the past year or so, reaching to a second floor.

Environmental consultant and researcher Florian Kroll, of Open Synergy , a sustainable development and complementary health agency, and partner, Helena Wagener, have been building their earth house since May 2005, very much on a trial and error basis, with lots of input from experts like interior designers, land surveyors, engineers and home builders.

“It is encouraging to see that earth building systems are entering the realm of mainstream architecture, design, construction and decor on a very practical level,” Kroll says.

Florian Kroll and Helena Wagener have been working on the house since 2005

The 80m² earth house , or nautilus, is taking shape in Oak Street, Linbro Park on a property of about an acre in size. The site contains a conventional house where Kroll lives at the moment.

A nautilus is a shell divided into several compartments within its natural spiral shape. The double-storey house is shaped in the same circular way, with walls dividing it into functions like kitchen, bathroom and living area.

“The spiral allows wind catchment and climate control, optimal orientation, passive solar gain, economic rainwater harvesting, and ergonomic flow of everyday activities using a minimum of building material,” Kroll explains.

The first walls were constructed as part of the 2005 Sustainable Built Environment Conference, with assistance from architect Etienne Bruwer, straw bale expert Pete Mackintosh and lime expert Jill Hogan.

“Earth is one of the most environmentally friendly building materials available; it is chemically inert and it does not release toxic vapours. Because it is breathable, it buffers moisture and temperature very well,” Kroll adds.

From a distance it looks a little like a brown doll’s house, but close up its walls consist of hard, packed earth flecked with bits of straw, with rectangular and arched windows set into its walls. It is roofless, with Kroll having had to adjust the angle of his splayed roof. He is finally happy that he has the correct configuration.

Inside, arched walls reach up into the sky, with a dozen or more large logs embedded on the west side, ready to take the roof. Inbuilt seats avoid the need for furniture, and a pizza oven will add to the cosiness in winter.

Recycled car windscreens have been used for windows; but, says Kroll, they can’t be opened and they scratch easily, so he’s considering replacing them with normal, wood-framed windows.

Earth houses usually have thick walls that absorb heat during the day, releasing it at night, negating the need for energy-consuming heating systems. And, because earth is not combustible, earth buildings are fireproof.

The house will be completed with a composting toilet, a grey water system, a rain water reservoir, and solar panels on the roof. Energy from the panels will be stored in a battery bank, inside the house. The rain water will be filtered to use for drinking and cooking.

Mixing the building material
Kroll has obtained his building material from a large hole at the site, where, he says, he digs to the subsoil, the third layer down. It’s best to use this layer of soil because what is needed is a mix of clay, silt and decomposed organic matter.

The soil is then sieved and laid out on plastic ground sheets. A hole is created in the middle and water is added. And here’s where the fun starts. You take off your shoes and with your feet you step on to the mix and knead it until it has a plasticity similar to conventional cement mortar. To this paste straw is added, and the mix is treaded further. The final result should be a smooth straw and soil mix, known as cob.

“The quality and composition of the soil used in the construction of earth houses has to be continuously monitored to assure strength and consistency,” Kroll says.

Big challenges
One of the big challenges with earth building is that the building must remain dry. To ensure this, deep trench foundations should be built, he explains. The house’s foundations are filled with compressed building rubble. This ensures good drainage under its walls, and prevents rising damp.

With cement prices rising, Kroll claims, using rubble saves on the overall cost of building the house.

Plastering the outside walls also ensures they remain watertight. And adding linseed oil to the cob gives a certain water repellency. “Careful design encouraging convection currents and regular air movement helps the building material to remain dry despite high humidity levels.”

Construction methods
Once the cob is stiff and difficult to pull apart, it is ready to use for construction. It is rolled into loaf-sized bricks and added to the walls.

Various mixtures can be used: these cobs can be used with posts in a wattle and daub structure; or they can be placed in a mould and dried in the sun. IN the rammed earth method, earth is rammed into a box mould and stamped down. The mould is removed and the process repeated.

Straw bales can also be used, set into a wall with spikes. Subsequent bales are stacked and pegged into place with long spikes. The straw bales are then sealed with a cob layer and plaster. This form of building is vulnerable to rotting, though, and it is imperative it’s kept dry.

Kroll has used straw bales on the western and south-western edges of the house - the colder sides of the dwelling - as they provide greater insulation. Similarly, more of the windows are on the north-facing side of the house, to catch as much sun as possible.

Sandbags are another method. The bags are filled with earth and stacked on top of one another, with layers of barbed wire between each bag allowing them to grip each other. “They are extremely stable and can resist earthquakes and major concussions.”

Environmentally friendly: the earth house in Linbro Park is steadily growing

Enquiries
Kroll gets enquiries every week concerning his house and its construction. A straw bale house is being built in Hyde Park and there is a cob house in Muizenberg, in the Western Cape.

“Each month brings news of earth buildings going up or being completed somewhere in the country. A plethora of synergetic or associated technologies and philosophies are starting to make a noticeable impact on our society and our mainstream economy,” he says.

“Any difference makes a difference,” says Wagener, referring to being enviro-friendly. It’s the little things that add up to making a difference, she adds. A permaculture garden will be created on the site, to make the couple as self-sufficient as possible.

So far, about R90 000 has been spent on building the earth house, and Kroll estimates that he will spend R100 000 in total. Most of that money has gone on labour costs. Some elements, like the roof poles, have had to be redone, adding to the cost.

And what’s next for Kroll? He’s thinking of building a small backpackers lodge, cottages, and a small eco village.