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 are 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. Even though the buildings in Sana’a are thousands of years old, they remain very contemporary. The ancient structures are still inhabited today, and most remain as private residences. They are well-insulated, sustainable and extremely adaptable for modern use. The architecture of the future?
Architects around the world are reviving mud construction, as they seek to construct sustainable buildings that can withstand extreme weather events such as flash floods and intense heat, as well as addressing the climate crisis.
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 the global temperature rise below the critical threshold of 1.5C. Swapping concrete for less polluting materials, such as mud, 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. Mud could be the perfect sustainable alternative to concrete. Constructing with mud has a very low impact on the environment and the material itself is fully recyclable.
The city of Djenné lies in the Niger delta region of central Mali. It was founded in 800 AD, and 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 re-clay the mosque, supervised by a guild of senior masons. The re-claying is an important symbol of social cohesion. Everyone takes part. Boys and girls mix the mud, women bring the water and masons direct the activity. Mud is very malleable and it responds easily to the changing demographics of a home. If the family grows, rooms and buildings can easily be added to the home, and if it shrinks, those rooms and buildings that are no longer needed, are left to decompose and turn back into soil.
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. Mud is a very inclusive material; poor and rich can build with it,” she says. “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. As you work with it, the material changes and responds.
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 gases. 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.
Mud structures are 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. Mud architecture can withstand extreme events such as earthquakes and heavy winds because of the ability of its structure to distribute the load across its surface, unlike concrete or cement.
Overall, mud makes for highly sophisticated building material, as well as accommodating flexible and sustainable designs. Well worth considering, if you can get over the stigma of living in a “mud hut”.