Belgian architect Jean Dethier’s new book The Art of Earth Architecture, published recently by Thames & Hudson, is a manifesto for the return of raw-earth building. He documents the history of this technique which stretches back centuries, but a third of the book is devoted to contemporary buildings constructed using the rammed-earth method.
Waugh Thistleton Architects constructed two new prayer halls at Bushey Cemetery in Hertfordshire using rammed earth, and the project was short-listed for the Sterling Prize in 2018, winning the RIBA National Award in the same year. We spoke to one of the practice’s founding partners, Andrew Waugh, about this emerging trend in construction.
Q: How do you make a rammed earth building?
A: There are different types of rammed earth, but generally it is made from a mixture of the soil on site, sand, loam, clay, gravel, silt and cement which is compacted between wooden or metal shutters. It’s like a recipe and every chef has their own way of doing it. After testing the composition and structure of the local soil, you create a formula that works with the design. You can’t be too evangelical about the purity or the percentage of cement you add. Our first sample for Bushey Cemetery was cement-free but rain reduced it to mud, so we added about 2% cement to help the building withstand the British climate.
Q: How is rammed earth a better alternative to concrete?
A: Rammed earth is highly sustainable as it has a high thermal mass and a 40th of the carbon footprint of concrete which is composed of 20% cement. It is also completely recyclable and has low transport emissions as the main material is already on site.
Rammed-earth buildings need to have walls that are considerably thicker than their concrete counterparts, but they are fire-proof, termite-proof, breathable and have insulating properties as they can absorb heat during the daytime and release it at night. This makes them popular in the developing world and in countries with extreme climates like Australia.
Concrete has a range of texture applications like wire brushing, carving and mould impressions. These aren’t an option for rammed earth as it dries too quickly, but it doesn’t need any adornment as its natural patina is so beautiful and full of character. Planners also love the fact that it is pertinent to the context and reflects the local environment.
Q: Why hasn’t it been adopted by the architecture industry in a time of climate-change targets?
A: Architects have been researching low carbon construction for 50 years now and have come up with very complex, worthy solutions like Passivhaus. We need to change the script to one of optimism and opportunity and push for a new age of simplicity in architecture that looks to the past.
Simple structures can be built using complex and sophisticated processes, but we need to move on from Modernism which dictated that buildings need to look brand new at all times. This has resulted in insane maintenance and cleaning costs, and we need to re-visit our relationship with buildings and our interaction with them.
Rammed earth buildings could be part of the solution for low-carbon, high-density housing, but they have their own characteristics, variations, texture and colour and a different kind of purity. They need constant renovation, but, as the old Chinese proverb says, there’s no such thing as a finished building.