Rammed Earth: the building material of the past, present and future

With a new Thames & Hudson book calling for the return of the raw-earth building, we speak to Waugh Thistleton Architects' Andrew Waugh to discover more about this sustainable material

Earth has been used as a building material for almost 10,000 years; across the world, different peoples and cultures have used unbaked earth to create a plethora of buildings – not just homes and dwellings, but fortresses, palaces and temples that have stood the test of time.

Recently, a new book on earth architecture was published by Thames & Hudson. Written by Belgian architect Jean Dethier, The Art of Earth Architecture is the culmination of 50 years of work, and is a manifesto for the return of the raw-earth building. Illustrated with 600 photographs, and around 100 drawings and architectural plans, The Art of Earth Architecture shows the extreme diversity of earth buildings.

Delving into the various earth-built masterpieces scattered across the globe (many of which are UNESCO world heritage sites), Dethier’s book looks at earth architecture historical, cultural and technical points of view. Interestingly, a third of The Art of Earth Architecture is devoted to contemporary buildings that have been constructed using the rammed earth method.

Image: Jim Stephenson

One such contemporary project that was created using rammed earth as its source material was the two new prayer halls at Bushey Cemetery. Designed by Waugh Thistleton Architects, a practice that focuses on creating thoughtful, sustainable designs, the Bushey Cemetery project was short-listed for the Sterling Prize, and won the RIBA National Award, in 2018. With this in mind, we spoke to one of the studio’s founders, Andrew Waugh, to discover more about the way rammed earth is making a comeback:

Can you tell us a bit more about yourself, and Waugh Thistleton Architects?

We set up WTa straight from University; in hindsight, a bit crazy, but I think it means we have a culture in the practice of constantly innovating – we’re used to starting from scratch! It was originally just me and Anthony on a big wooden table, and we were designing night clubs, bars and restaurants… now we have seven big wooden tables, and we design high density social housing, very green office buildings, crematoria and more! We specialise in everything – and are always, always researching.

Image: Lewis Kahn

When did you / the studio first come across rammed earth as a material?

Magazines and books; I came across photos of the City of Sana’a in Yemen as a student and got a little obsessed… Then went to see Martin Rauch’s house – but he wasn’t in.

How do you make a rammed earth building?

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.

Image: Jim Stephenson

How is rammed earth a better alternative to concrete?

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.

Does a rammed earth building always use local soil?

Hopefully... as much as possible - it depends on a few factors such as clay content etc.

Image: Jim Stephenson

Why did Waugh Thistleton Architects choose this material for Bushey Cemetery?

When we were first drawing Bushey and thinking about construction materials, it immediately seemed perfect for the building, for the use and for the site. Often we think about structure and skin as separate entities... but it seemed to me early on that we wanted to have a solid building - one that appeared rudimentary. A rabbi had told me that a prayer hall should be no more than a shelter… nothing to distract you but a place of contemplation. So the notion of a simple, pure form and honest material was always with us.

How did it feel for Bushey Cemetery to be recognised by the Stirling Prize and the RIBA National Award?

Fabulous. We were ecstatic. It shouldn’t mean as much as it did, but we’ve always been a bit on the outside of the profession. Starting straight from school and building mostly in timber, we’ve never really done any competitions – so I guess this acknowledgement from people we respect felt like being let in from the cold! And then also for a mud building! 

Image: Blake Ezra

Why hasn’t rammed earth been adopted by the architecture industry, in a time of climate-change targets?

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.

What would you say to other architects/designers about using rammed earth as a material?

Go for it! It’s gorgeous. Find a great contractor and a super engineer… and wonderful client. Those are the real ingredients for a successful rammed earth building.

Anything else to add?

I’d like to thank my Mother for her constant encouragement. 

Feature image: Lewis Kahn

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