<div><span style="font-size: 1rem;">It was used to build the Great Wall of China and Spain's mediaeval Alhambra Palace -- and now earth is back in vogue as a building material.</span><br></div><div><br></div><div>Climate change has spurred renewed interest in the ancient technique which sees polluting concrete swapped where possible for earth.</div><div><br></div><div>For centuries, mud and clay were an abundantly available way to put a roof over one's head, but earth's environmental credentials are behind its modern-day resurgence.</div><div><br></div><div>"A kilo of cement emits a kilo of CO2. Whereas a kilo of earth emits none," Xavier Chateau of the Navier Laboratory at the French National Centre for Scientific Research said.</div><div><br></div><div>"If we could reduce by 25 percent the volume of cement consumed globally it would be equivalent to negating the impact on the climate of all air transport," he estimated.</div><div><br></div><div>Known as rammed earth construction, the practice dates at least as far back as the Neolithic era.</div><div><br></div><div>It involves compacting certain soils into a mold, of sorts, to make building blocks or build up whole walls, layer by layer.</div><div><br></div><div>More than two billion people across some 150 countries live in buildings made of earth, according to a 2006 guide on earth building by French authors Hugo Houben and Hubert Guillaud.</div><div><br></div><div>Advocates say it can help reduce reliance on concrete, which accounts for about eight percent of global CO2 emissions.</div><div><br></div><div>Earth also has a high thermal capacity by self-regulating its humidity, is fireproof, non-toxic and can be completely recycled.</div><div><br></div><div>But it has downsides too, not least the cost, given the need to find builders qualified in ancient techniques.</div><div><br></div><div>- 'Earth concrete' hybrid -</div><div><br></div><div>Confronted with flooding, earth-constructed buildings need protection, as earth also has its weaknesses.</div><div><br></div><div>A four-storey rammed earth building crumpled in France's southeastern Rhone region in November, while a house collapsed in the nearby department of Isere on December 22, according to local press reports.</div><div><br></div><div>Often substances such as lime or straw can be added to the earth to stabilise it and bolster its durability.</div><div><br></div><div>French building material firm Saint-Gobain is experimenting with a hybrid system of "earth concrete", combining excavated earth from construction sites, steel industry waste and hemp.</div><div><br></div><div>But purists see it as verging on heresy, in a country due to complete a 9,000-seat concert coliseum north of Paris next year using recycled excavated earth.</div><div><br></div><div>"It's not the same material at all," complains architect Paul-Emmanuel Loiret, who manages La Fabrique outside Paris where blocks and bricks of compressed earth are made from construction rubble.</div><div><br></div><div>Urging a "complete and rapid decarbonisation" of construction, he complained that EU laws "impose on us materials 10 to 20 times more durable than those which we need."</div><div><br></div><div>But, said Chateau: "In Africa, in Burkina Faso or Malawi, it's become a kind of artisanal savoir-faire to stabilise raw earth with cement at the foot of the building to solve the problem of water" encroachment.</div><div><br></div><div>- 'Huge demand' -</div><div><br></div><div>Austria has Europe's only factory to date making low-energy prefab homes using rammed earth methods.</div><div><br></div><div>The site, in the western village of Schlins on the Liechtenstein border, creates foundations, floors and walls using chalk, clay, chopped straw, lime or gravel.</div><div><br></div><div>A machine pounds the earth which is compacted into a vast casing to produce 40-metre (130-foot) long walls.</div><div><br></div><div>Once dried and cut to size, the blocks are sent off to be assembled.</div><div><br></div><div>"Given the ecological challenge and the problem of energy, huge demand is emerging for this material," said environmentalist, entrepreneur and former potter Martin Rauch, who built the factory.</div><div><br></div><div>Architect Sami Akkach who works with Rauch said they use earth from the surrounding area, building and excavation sites.</div><div><br></div><div>"It must contain clay, gravel, angular rather than round so it really sticks," Akkach said.</div><div><br></div><div>Rauch has several earth-constructed buildings to his name, including his home whose exterior walls include terracotta designed to act as a brake on rain and erosion, a throwback to ancient methods used in Saudi Arabia.</div><div><br></div><div>He says the factory boasts Europe's longest earthen wall -- at 67 metres -- and he believes the demand is there for more projects using rammed earth.</div><div><br></div><div>"The problem is there are not enough artisans and people are still too afraid of this natural material," he said.</div><div><br></div><div>He added that hopefully people will realise that "earth structures will last for centuries, if they are built correctly." - AFP&nbsp;</div><div><br></div><div>bnbd24/fas</div><div><br></div>