Building for tomorrow: back to earth

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Did you say "sobriety"? In the face of global warming and galloping urbanization, it's becoming urgent to develop energy-efficient homes and offices. Why not turn to traditional materials like earth, which is carbon-free and local? Here's a primer on sustainable building materials, with a focus on raw earth, an ancestral material that's enjoying a renaissance.

To build the 246 billion square meters that saw the light of day on the planet in 2020 (+1% compared to 2019), cement and steel remain by far the two leading materials used and the biggest CO2 emitters. Other materials are currently gaining ground.

Carbon emissions from the building sector (AFP - Jonathan Walter)

To make construction greener, steelmakers, especially in Europe, are planning to produce "green" steel by 2050 by replacing CO2-emitting coal with green hydrogen to smelt iron ore. But the investment required is huge, and this will increase costs by at least "30%", warns Christian Gollier, Managing Director of the Toulouse school of economics.

B. CONCRETE + CEMENT

Fourteen billion cubic meters of concrete are poured every year, according to the London-based World Cement and Concrete Association.

Between 2011 and 2013, China alone consumed 50% more cement than the United States did in the entire 20th century, according to British geographer David Harvey. Yet concrete emits more CO2 than aviation due to the presence of cement, whose binder, called clinker, must be heated to 1,400 degrees for its manufacture.

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A scientific hope, however faint: by biomimicry with corals, it is possible to manufacture cement from calcium carbonate, which sequesters CO2.

In the meantime, for mass construction, the whole sector is betting on decarbonated concretes, notably by replacing cement binder with "slag", a waste product from the steel industry. But the " The steel industry itself is a major emitter of CO2" points out Christine Leconte, President of the French Architects' Association, who is betting on "local" materials, such as earth or stone, to reduce emissions.

C. AIR CONDITIONING - HEATING

According to a study published in March by the National Renewable Energy Laboratory in Palo Alto (USA), air conditioning alone is responsible for 4% of global emissions. A vicious circle: the warmer the planet gets, the more air conditioners are needed.

Some architects, like Zimbabwean Mick Pearce, have designed biomimetic air-conditioning systems inspired by nature. Modeled on termite mounds, which regulate their own temperature by leaving a multitude of ducts to allow air to circulate, he designed Harare's largest commercial building, Eastgate. The building cools itself at night by storing cool air and expels hot air during the day.

Some ventilation or heating systems are based on swarm logic, where appliances in the same building are interconnected to regulate peak demand.

E. ENERGY EFFICIENCY

This is the main challenge, as the type of energy used to heat or cool a building determines the weight of its emissions. In 2020, global investment in the sector jumped by an unprecedented 11.4% to some $184 billion, according to a report by the UN Global Building and Construction Alliance. But all this is still a long way from the target that needs to be reached to meet the commitments of the Paris climate agreement: CO2 emissions from the building sector should decrease by 50% by 2030 compared with 2020, or 6% per year, which implies a 45% drop in energy consumption per square meter worldwide, a pace five times faster than has been achieved to date.

I. INSULATION

Faced with heat waves or cold winters, it's better to invest in building envelope insulation than to increase air conditioning or heating. Walls retain heat better than glass, but double-glazing is on the increase everywhere, and even triple-glazing for certain "passive" buildings in northern Europe.

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J. "RAIN GARDEN

Designed to capture rainwater running off the roof of a house or driveway, it retains water briefly after precipitation. These gardens, made up of rocks, plants and shrubs adapted to dry conditions, are part of nature-based solutions for adapting to global warming.

M. BIO OR GEOSOURCE MATERIALS

Wood, hemp, cork, flax, straw, cellulose wadding: these materials, made from renewable plant matter, make a significant contribution to storing atmospheric carbon and preserving natural resources. Their use is encouraged in construction, insulation and renovation.

The problem is that, in Africa, where some of these materials have long been used for traditional housing, galloping urban growth is essentially via cement or steel," laments geographer Armelle Chopin, author of "Matière grise de l'urbain, la vie du ciment en Afrique" (2020).

R. REDUCE/RECYCLE/USE

We try to give a second life to materials, sometimes they come from demolition sites, we try to transform obstacles into solutions. Reducing materials is the best way to reduce the building's carbon footprint. "These are the words of Irene Perez and Jame Mayol, who founded the Ted'Arquitectes architectural practice in Palma de Mayorque (Spain). Like a growing number of architects, they both favor the reuse of materials.

The construction of a single-family home consumes 40 times more resources than renovation, and that of a multi-family building around 80 times more, adds the French Environment and Energy Management Agency.

A worker at work on a building constructed using the pisé technique, which consists of compacting wet earth in a formwork, in Lyon on June 27, 2019 (AFP - Romain Lafabregue)

T - RAW EARTH

Among the techniques brought back into fashion: Pisé, compacted and cased earth, torchis (raw earth cut with straw or animal dung), bauge (successive layers of torchis rammed without a framework), or raw earth.

Earth, an inexpensive, local material, helps to regulate humidity and, above all, smooth out indoor temperatures, especially in hot weather. It can be found in Canada (Nk'Mip Desert Cultural Center), in Austria's Vorarlberg region, or in the form of prefabricated adobe panels in Lyon.

Workers at work on a building constructed using the pisé technique, which involves compacting damp earth in a formwork, in Lyon in central-eastern France on June 27, 2019 (AFP - Romain Lafabregue)

In 2021, the Renzo Piano studio will deliver to an Italian NGO a children's hospital in Entebbe, Uganda, made entirely of adobe from excavated soil and topped with photovoltaic panels.
German-Burkinabé architect Francis Kéré, winner of the prestigious Pritzker Prize in 2022, has made building with local materials, including earth, his trademark, stamped "sustainable high tech".

U - URBANISM

The experts recommend curbing new construction, encouraging renovation in city centers, halting urban sprawl and even "rebuilding the city on the city".

V - PHOTOVOLTAIC GLAZING

Glass panels generate electricity from filtered sunlight. Still expensive, this emerging technique is a precursor to tomorrow's connected buildings, but is hampered by a shortage of materials, particularly silicon.

Raw earth, a material for the ecological transition

In the collective work " Today's earthen architecture "published in 2017 by Museo (1)ecological architecture Dominique Gauzin-Müller explains that raw earth, one of the earliest building materials, "is conquering the field of contemporary architecture thanks to the hundreds of buildings of exceptional aesthetic and technical quality that are emerging all over the planet." "Made from adobe, bauge, compressed earth blocks (CEB), pisé or torchis, [these inspiring examples] encourage the rediscovery of an abundant and inexpensive material, which could cover part of the need for economical and comfortable housing."

"The presence of earthen walls guarantees a healthy indoor climate: moisture regulation, absence of toxic products, absorption of odours and noise. Their thermal inertia also ensures a naturally pleasant temperature: heat accumulated during the day in the thickness of the walls is diffused throughout the building at night." "Building with raw earth is a major contribution to the ecological and societal transition."

For example, the winners of France's first Prix National des Architectures en Terre Crue have demonstrated the value of this material: the European Conservatory of Soil Samples in Orléans. This ambitious building, well suited to the needs of an important scientific institution with a European vocation, is set to become a showcase for the earth, both that cultivated by farmers and that used by architects. This "adobe safe for a land bank" was an explicit wish of the client.

European Soil Sample Conservatory - Orléans (45)

Or the Kiethon day-care center for autistic people, near Rennes: interior architect Léna Riaux designed the adobe walls surrounding the atrium of this day-care center for autistic people "like a matrix". An intimate, sensual and reassuring environment that promotes - for the first time in France - the psychotherapeutic virtues of earthen constructions.

Espace Kiethon in Médréac, Ille-et-Vilaine, Brittany

Another example is this detached house, designed by Thomas Jay of the Caracol agency and built by the Scop Caracol, which blends grains and fibers in a mix of innovative techniques: central wall in load-bearing adobe, poured earth partitions with lost reed formwork, earth plaster on straw walls. A blend of bio-sourced materials to create a warm and welcoming atmosphere.

Private detached house in Corbel, Savoie, Rhône-Alpes

Architecture in raw earth, a bio-sourced material available worldwide, is on a roll. Renzo Piano, Norman Foster, Herzog & de Meuron, Wang Shu and other stars of world architecture are rediscovering this ancestral material, and more and more projects of high technical and aesthetic quality are emerging in France. To encourage rapid recognition of these buildings by the profession and the general public, we need to publicize them by highlighting the skills of the architects who designed them and the craftsmen who built them.

(1) Published under the auspices of the UNESCO Chair in Earthen Architecture and Sustainable Development. Housing, facilities, business buildings, interior and exterior fittings... 40 projects described in the book "Today's Earthen Architecture" were chosen by a jury of experts from 357 candidates from 67 countries, on the occasion of the first World Prize for Contemporary Raw Earthen Architecture, the TERRA Award, launched in 2015, to prove the modernity of the earth material and contribute to its growth.

Header photo TECLA - Technology and Clay is the first innovative model of an eco-sustainable 3D-printed house made from local raw clay in Massa Lombarda, Ravenna. A project by MC A Mario Cucinella Architects and WASP World's Advanced Saving Project.  
Image courtesy of Mario Cucinella Architects, photo by Iago Corazza.

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