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October 19, 2012 7:00 pm
The fabled cities of Jericho, Ur and Babylon were built entirely of earth. So were sections of the Great Wall of China. Today, around half the world’s population live in dwellings made of the material and, from Lutyens to Gaudí, many of the world’s best-known architects have experimented with it. Yet only recently has earth crept on to the curricula of architecture and engineering schools, and few laymen think of it as a building material.
“With industrialisation and the railway, it became easier to transport energy and building materials, so it wasn’t necessary to build with earth any more,” says Martin Rauch, a ceramic artist turned architect championing the use of earth for sustainable construction. It became a poor man’s material and the image is hard to shake. But in the past 15 years, rammed earth has returned to the limelight as human and environmental health have become key concerns.
Rauch has used rammed earth to build cinemas, churches and chapels – and his own family home in Austria. The materials used in the 18 months of its construction were local, so minimal energy was used in production and transportation. With 47 per cent of anthropogenic carbon dioxide emissions attributable to the construction industry in the UK, for instance, such alternative methods are significant.
The ability of earth to moderate humidity and temperature is another advantage, which eliminates the need for expensive central heating and air conditioning. “It’s a wonderful climate – in the winters it is warm and in summer cool,” claims Rauch.
A central concern of sceptics is durability. However, the compressive strength of rammed earth (its ability to withstand squashing) is two-thirds that of concrete at a similar thickness. And in the city of Shibam in Yemen, rammed earth buildings of five or six storeys were built in high density urban spaces and have survived around 1,700 years.
The fear is that exposure to rain and moisture will cause walls to slump but, with a good hat and shoes, little else matters: strong foundations and an overhanging roof protect earth walls from overexposure to the rain. Rauch designs for “calculated erosion” – changing aesthetics are part of the appeal. Every few layers, he inserts stone blocks into the surface of earth walls. These protrude as the earth erodes around them, acting as a buffer against rain running down the surface of the building.
Research conducted by the Scottish government in 2001 highlights the key issue – people used to accept that they would have to maintain their homes. “The longevity of earth buildings is due, in part, to the regular maintenance regimes that were integral to traditional practice. A change of attitude is necessary if modern earth buildings are to survive equally well as current construction practice promotes ‘maintenance-free’ products such as cement renders and masonry paints.”
Building regulations for rammed earth vary around the world. “If I built my house in Germany, I would have needed a licence costing between €20,000 and €30,000,” says Rauch. “In Austria and Switzerland it is easy. In Italy rammed earth is not allowed for structural work.”
In the UK it can actually be easier to secure planning permission if you’re building with rammed earth, as local authorities often object to plans that require material to be taken off site. There are groups trying to develop global practice guidelines and the Southern African Development Community is ahead of the game, with 15 countries sharing a harmonised code written by British consultant Rowland Keable. In terms of European guidelines, Earth Building UK recently won a European bid to develop shared training standards for rammed earth construction.
The construction process is not dissimilar to building a sandcastle. Earth is collected, its consistency checked, and organic matter that will decompose is removed. Next, formwork is brought in; this is the frame into which the earth is, quite literally, rammed layer by layer, either manually or by pneumatic rammers. The earth begins to cure straight away and continues to do so for months or years, depending on the local climate. Without baking, the wall is complete and the process can be repeated.
This process requires significant amounts of labour and leaves little room for the mechanisation and profits that are seen as driving economies. However, Anna Heringer, a Royal Institute of British Architects award-winner who has extensive experience with rammed earth in the developing world, views the labour intensity of construction as a bonus.
“There are going to be 7bn people on this earth. The cheapest technology is now cheaper than even the cheapest labour on earth. We need some good employment opportunities, and not just for specialists.”
Heringer sees rammed earth from a social justice perspective. “We often think of sustainability in terms of high-tech solutions and it isn’t possible for everyone in the world to have high-tech solutions. That’s exclusive, which isn’t sustainable. Building with earth, you can have a lot of people involved – it’s about communities too.” This ideology echoes that of the French architect François Cointeraux (1740-1830). The father of pisé de terre technique, driven by the revolutionary spirit of “honourable labour”, wrote books instructing the French public on how to build their own earth homes.
A team of 150 students, Loeb fellows and members of the public worked under Rauch and Heringer to build the Mud Hall project at Harvard’s Graduate School of Design in April 2012. “The space we chose was very prominent at the front of the school but it was hostile, windy land that wasn’t used and the idea was not just to say there’s something wrong but to take our creativity, our hands and the earth and transform it into a living space for people,” says Heringer. The aim was to change conventional thinking about sustainable development by building with rammed earth, and although the plan was to use the project as a demonstration and then demolish the walls by May, they have been kept. “Now the homeless are sleeping there at night, which is really quite a compliment,” she says.
Human connection with the aesthetic of earth is another factor. “We’d get people walking past and they would stop to touch the wall, even though the colour is quite like concrete,” Heringer continues. “There is a presence with this material I can’t explain. Now we barely touch earth – just the dirt at the bottom of our shoes and in flower pots – and there’s a longing for it.”
Depending on the earth selected, the colour of a building can be varied, the ramming process can be designed to produce layering effects and the formwork can be moulded so patterns are embossed in the walls. The visitor centre at the Eden Project in Cornwall, southern England, includes a wall made of locally sourced rammed earth in order to make the most of the site – a China clay quarry with a seam of pink clay running through it.
Rauch is aware of the limits, however. Certain structures such as foundations for buildings, ceilings and bridges are not possible in earth. So he suggests using appropriate, context-specific materials together. “I represent the connection of earth construction with modern material but in a sustainable way.”
In the western world, most earth constructions are actually stabilised rammed earth, where cement is added to the mud. “This is the wrong way to do things,” says Rauch. “If there is cement in the mix it is not real earth – it’s rammed concrete.” In stabilised rammed earth, around 8 per cent of the material is cement. Rauch strongly believes it isn’t necessary; we have built for 10,000 years with pure earth and he feels that the climatic and environmental qualities of the material are lost with such contamination. Heringer adds that when cement is mixed with earth, “you can’t totally recycle it”. “We are not building for eternity, that’s an idealistic thought. Some day it will all return to the ground and then there’s the question of environmental impact.”
Having used earth in construction around the world, in the monsoons of Bangladesh and dry summers of Morocco, Heringer has proved that cement is not required with innovative, context-specific design.
The newest innovation in the field is the introduction of prefabricated elements, as pioneered by Rauch himself. Local excavation and ramming aren’t possible in dense, urban environments. The solution is to make a long wall, some 40 metres, of rammed earth in a factory. This is sawn into five-tonne segments and transported to the site. The wall is reassembled with mud to weld the segments together so the joints aren’t visible, a bit like pottery.
Building time is saved, as two months of work in the factory translates to two weeks of building on site, and the space required to assemble a wall is a fraction of that required to gather earth and ram it.
Yet rammed earth remains, to the architecture world, what haute couture is to fashion: those in the industry revere it but the rest of us have barely heard of it.
How on earth ... ?
Earth is a cheap, renewable and widely available alternative to environmentally costly conventional building materials. During the Great Depression, US policy makers considered it for housing; seven experimental rammed earth homes were built on the Gardendale Homestead in Alabama but a full-scale federal initiative never followed.
Unlike other sustainable building materials, such as straw bale and timber, earth is reusable and non-flammable. When tested by Australian Standards, a rammed earth wall 300mm thick withstood direct flames for four hours.
The amount of energy used in producing rammed earth is relatively low. The Scottish government’s Central Research Unit estimates: “To prepare, transport and construct earth materials commonly requires about 1 per cent of the energy required by the commonly used cement-based alternatives.”
Walls made from rammed earth keep humidity levels between 40-60 per cent, the ideal range for asthma sufferers. This benefit is lost when the earth is stabilised with cement.
Rammed earth has a high thermal mass, which means it is able to store and release heat. Internal temperature fluctuations are limited as the walls absorb heat in the daytime to release it internally as temperatures fall.
Countering the high thermal mass is low thermal resistance. As rammed earth walls allow heat to flow through them easily, insulation may be required in cold climates.
The cost of rammed earth construction worldwide
The cost of building with rammed earth varies, not only with complexity of design but also with local context. Is the local soil appropriate or will it be necessary to transport earth to the site? What is the cost of labour in the area?
Building with rammed earth is relatively labour intensive. This means it is a cheaper alternative to modern materials in developing nations where wages are low, but comparatively expensive in the industrialised world where mechanisation is preferred.
In Australia, rammed earth constructions tend to be relatively expensive. Luigi Rosselli, an Australian architect known for his work with rammed earth, says the cost of a load-bearing wall built to a high standard with the necessary finishes would be about US$421 per square metre in double brick, $737 in rammed earth, $789 in concrete and $947 in stone.
In the UK: Scotland’s Central Research Unit undertook a study in 2001, which estimated that there were 500,000 inhabited earth buildings in the UK; earth was the principal material used in Scottish construction until the 18th century. Rowland Keable has extensive experience working with rammed earth in the UK and found that the cost can vary hugely. It begins at zero cost for a self-build community project. In general, he estimates a cost of $250 per sq m for a wall in rammed earth, nearer $790 for double-brick.
In Bangladesh Simple Action for the Environment constructed a rural home from rammed earth in 2011. Each sq foot of wall cost $0.34 to build. It would have cost $0.62 with brickwork.
Stabilised and insulated rammed earth, as offered by construction firm Sirewall, costs 12 per cent more than the stick-frame alternative, according to the company’s own figures. A 3,500 sq ft property would cost $1,565,754 to build with Sirewall but $1,375,758 using stick frame, it says.
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