The Sustainable Cities Made From Mud
In Yemen’s ancient walled city of Sana’a mud skyscrapers soar high into the sky. The towering structures are built entirely out of rammed earth and decorated with striking geometric patterns. The earthen buildings blend into the nearby ochre-coloured mountains.
Sana’a’s mud architecture is so unique that the city has been recognised as a Unesco World Heritage site.
“As an outstanding example of a homogeneous architectural ensemble reflecting the spatial characteristics of the early years of Islam, the city in its landscape has an extraordinary artistic and pictorial quality,” Unesco writes in its description of Sana’a. “The buildings demonstrate exceptional craftsmanship in the use of local materials and techniques.”
Even though the buildings in Sana’a are thousands of years old, they remain “terribly contemporary”, says Salma Samar Damluji, co-founder of the Daw’an Mud Brick Architecture Foundation in Yemen and author of The Architecture of Yemen and its Reconstruction. The ancient structures are still inhabited today and most remain private residences.
Damluji says it is easy to see why these mud buildings have not lost their appeal – they are well-insulated, sustainable and extremely adaptable for modern use. “It is the architecture of the future,” says Damluji.
Architects around the world are reviving raw-earth construction as they seek to construct sustainable buildings that can withstand extreme weather events such as flash floods and intense heat. Could this ancient form of architecture influence the design of our future homes and cities? Could this back-to-basics technique provide an important solution to the climate crisis?
Construction’s climate problem
The construction industry accounts for 38% of global carbon dioxide emissions. The building sector has an important role to play if the world is to meet its goal of reaching net zero by 2050 and keep global temperature rise below the critical threshold of 1.5C.
Swapping concrete for less polluting materials is critical to achieving our climate goals, scientists warn. Concrete, a staple of modern construction, has a huge carbon footprint. Building with concrete accounts for around 7% of global CO2 emissions – substantially more than the aviation industry which is responsible for 2.5% of emissions. Worldwide 4 billion tonnes of cement, the key component of concrete, is produced each year.
“We cannot live in these concrete jungles anymore,” says Damluji. “We have to consider the environment and biodiversity. We cannot construct in isolation.”
Mud could be the perfect sustainable alternative to concrete, according to Damluji. Constructing with mud has a very low impact on the environment and the material itself is fully recyclable, she says.
Reviving an ancient tradition
The city of Djenné lies in the Niger delta region of central Mali. Founded in 800 AD, it became an important meeting place for traders travelling from the Sahara and Sudan. Djenné is known for its magnificent earthen architecture, especially its Great Mosque which is the largest mud building in the world, standing almost 20m (66ft) tall and built on a 91m-long (300ft) platform.
Every year the residents of Djenné gather together to repair and reclay the mosque, supervised by a guild of senior masons. These master builders are revered for their expertise and artistry in Malian society, says Trevor Marchand, emeritus professor of social anthropology at London’s School of Oriental and African Studies and author of The Masons of Djenné.
“Master builders are recognised for their supernatural powers to bring protective elements to the buildings and people who live there,” says Marchand.
The re-claying is an important symbol of social cohesion, says Marchand. “Everyone takes part. Boys and girls mix the mud, women bring the water and masons direct the activity.
Djenné’s mud architecture is constantly changing as residents re-clay, repair and rebuild their homes.
“There is a dynamism to it,” says Marchand. “Mud is very malleable and it responds to the changing demographics of a home.” If the family grows, buildings can easily be added to the home and if it shrinks, buildings are left to decompose and turn back into soil.
The ancient building practice is inspiring modern-day architects, such as Serbian Dragana Koji?i?, who specialises in raw-earth construction.
“Our ancestors were really clever and really practical – they used what they had around them,” says Koji?i?. “The earth was everywhere and it could be used for everything: walls, floors, ceilings, stoves and even roofs.”
Koji?i?, who completed her training at the Centre for the Research and Application of Earth Architecture, restores and builds earthen houses across Serbia, reviving ancient building methods.
“Mud is contagious – it is love at first touch,” she says. You don’t need to wear any protective gear when handling the material, she adds. “With earth, you can just play.”
Anna Heringer, an Austrian architect who creates buildings using natural materials such as mud and bamboo, agrees. “It is a wonderful feeling to touch the earth,” she says. “You don’t need any tools to build with it, you just use your hands.”
Heringer has been working with mud for almost 20 years and has designed many notable earthen buildings, including the METI handmade school in Rudrapur, Bangladesh, for which she received the Aga Khan Award for architecture in 2007. “Mud is a very inclusive material; poor and rich can build with it,” she says.
The METI handmade school was built entirely with local materials, such as mud, straw and bamboo, and constructed by a team of local builders, craftsmen and the students themselves.
“Earthbound materials such as loam and straw are combined with lighter elements like bamboo sticks and nylon lashing to shape a built form that addresses sustainability in construction in an exemplary manner,” the Aga Khan jury said.
“Mud is the champion of future sustainable construction,” says Heringer. “It is the only material we can recycle as often as we like, without using any energy,” she says. “It actually gets better the more you use it.” It’s a bit like a dough, Heringer says – as you work with it, the material changes and responds.
But using mud for construction should be done in a sustainable way and should not reduce land availability for growing crops, says Marchand. “It can be a solution, but only on a certain scale,” he says, noting that the global population is expected to reach 9.7 billion people by 2050, mounting pressure on land.
Healthy, resilient buildings
One of the best qualities of mud buildings is that they are warm in the winter and cool in the summer, architects say. Mud walls have a high thermal mass which means they slowly absorb heat and store it, preventing the house from becoming too hot.
“Mud walls collect heat during the day from solar radiation and release it at night. The temperature never fluctuates – it’s always at a comfortable level,” says Pamela Jerome, a US architect and president of the Architectural Preservation Studio, which focuses on restoration projects around the world.
This reduces the need for air conditioning units, which consume large amounts of electricity and contain refrigerants that are potent greenhouse gas emissions.
In a 2021 report, the UK’s Environmental Audit Committee recommended using “sustainable, bio-based and breathable” products, such as clay and lime-based plasters and natural fibres, to improve the insulation of existing homes.
“In comparison to buildings constructed of concrete or corrugated metal, mud brick buildings keep relatively stable interior temperatures across a 24-hour period and thus supply inhabitants with far superior thermal comfort,” says Marchand. “An added bonus is that the thick mud-brick walls also reduce noise levels from outside or next door.”
The breathable nature of mud has other benefits too. Mud is porous and allows moisture into the house, improving the indoor air quality. “The earth has the ability to absorb excess moisture from the air, and to release it, if necessary, which is why we say that these houses ‘breathe’,” says Koji?i?.
“They are healthy buildings which breathe in the same way we breathe and have skins that adapt to hot and cold,” says Damluji. “The way they are constructed is in reference, in proportion even, to the human body.”
Mud structures are also incredibly sturdy and resilient to extreme weather, such as heatwaves, floods and droughts, which scientists say will become more frequent and intense as temperatures continue to rise. The UN’s Intergovernmental Panel on Climate Change (IPCC) warned in a report this year that cities and settlements are largely unprepared to cope with extreme weather events. To avoid costly damages and protect people, they must invest in climate-resilient buildings and infrastructure, the IPCC said.
Earthen architecture can withstand extreme events such as earthquakes and heavy winds “because of the ability of its structure to distribute the load that it faces on its surface, unlike concrete or cement,” says Damluji. But mud building’s resilience to earthquakes depends on the intensity of the seismic waves and the soil in which they are built, says Jerome.
Mud buildings are “also protected from seasonal rains and flash floods due to the damp-proof and protective external rendering used in several layers of refined mud, ash and lime coating and plaster”, says Damluji.
The impact of flooding on mud buildings varies, depending on whether they are built in a flood plain and have strong foundations, according to Jerome.
A severe flood in the Hadhramaut region in east-central Yemen in 2008 damaged 5,000 mud buildings, which had mostly been built on a flood plain, with few or no foundations, she says. The flood damage in Yemen’s nearby desert valley Wadi Dawan was far less severe because the mud dwellings’ foundations are more than 1.5m (4.9ft) deep and built of dry stone, which means water does not rise up through the soil, she adds. Paths in the valley are “designed as breakwaters that channel water into the irrigation channels of the date palm groves. Only about 25 buildings were impacted throughout Wadi Dawan”.
People who wish to live in a modern, comfortable home should consider one made of mud, architects say. “Mud buildings are extremely adaptable,” says Damluji. “If you want to pull a wall down or change the design, you can recycle all the materials.”
Overall, this makes for highly sophisticated as well as sustainable design, says Jerome. “Every mud house is comfortable, can be totally adapted and easily retrofitted with electricity and plumbing.”
Written by Isabelle Gerretsen