Workers work at a construction site in Beijing on March 10, 2019 (AFP/GREG BAKER)
Faced with global warming and rampant urbanization, should we develop offices and homes with high energy efficiency and smart technologies, integrating air conditioning and vegetation, return to traditional materials such as earth, low-carbon and local, or both? ABC.
A. STEEL (GREEN)
To build the 246 billion square meters that saw the light of day in 2020 on the planet (+1% compared to 2019), cement and steel remain by far the first two materials used and the most CO2 emitters.
Carbon emissions from the building sector (AFP/Jonathan WALTER)
To green construction, steelmakers, especially in Europe, plan to produce “green” steel by 2050 by replacing CO2-emitting coal with green hydrogen to smelt iron ore. But the investments to be expected are gigantic and this amounts to increasing the costs by at least “30%”, warns Christian Gollier, director general of the Toulouse school of economics.
B. CONCRETE + CEMENT
Fourteen billion cubic meters of concrete are poured per year according to the London-based World Cement and Concrete Association.
China alone, between 2011 and 2013, consumed 50% more cement than the United States throughout the 20th century, underlines the British geographer David Harvey. However, 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.
Even a tenuous scientific hope: by biomimicry with corals, it is possible to manufacture a cement from calcium carbonate, which sequesters CO2!
In the meantime, for mass construction, the entire sector is banking on low-carbon concrete, in particular by replacing the cement binder with “slag”, a waste from the steel industry. But the “steel industry is itself a major emitter of CO2”, notes Christine Leconte, president of the Council of the Order of Architects in France, who is betting instead on “local” materials, earth or stone, to reduce emissions.
C. AIR CONDITIONING – HEATING
According to a study by the Palo Alto National Renewable Energy Laboratory (USA) published in March, air conditioning alone is responsible for 4% of global emissions. Vicious circle: the warmer the planet, the more air conditioners there are.
Air conditioning units in Hong Kong on August 11, 2017 (AFP/Archives/TENGKU Bahar)
Some architects like the 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 allowing air to circulate, he designed Harare’s largest commercial building, Eastgate. The building cools at night by storing cool air and expels hot air during the day.
Some ventilation or heating systems based on the operation of bees in a hive (swarm logic), where the devices in the same building are connected to each other, also make it possible to regulate peak demand.
E. ENERGY EFFICIENCY
This is the main challenge because 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 an unprecedented 11.4% to some $184 billion, according to the report by the UN’s Global Building and Construction Alliance. But all this remains far from the objective to be achieved in order to meet the commitments of the Paris climate agreement: CO2 emissions from buildings should decrease by 50% by 2030 compared to 2020, i.e. 6% year, which implies a 45% reduction in energy consumption per square meter in the world, a rate five times faster than what has been done until now!
I. INSULATION
Faced with heat waves or winter cold, it is better to invest in the insulation of the building envelope than to increase the air conditioning or heating. Walls retain heat better than windows, but double glazing is developing everywhere, even triple glazing for certain “passive” buildings in northern Europe.
J. “RAIN GARDEN”
Designed to capture rainwater that runs 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 the nature-based solutions to climate change adaptation.
M. BIO MATERIALS OR GEOSOURCES
Wood, hemp, cork, linen, straw, cellulose wadding: these materials, made from renewable plant material, contribute significantly to the storage of atmospheric carbon and the preservation of natural resources. Their use is encouraged as much for construction as for insulation and renovation.
Problem, in Africa, where some of these materials have long been used for traditional housing, galloping urban growth is mainly done via cement or steel, deplores the geographer Armelle Chopin, author of “grey matter of the urban , the life of cement in Africa” (2020).
A. REDUCE/RECYCLE/USE
“We try to give materials a second life, sometimes they come from the demolition site, we try to turn obstacles into solutions. Reducing materials is the best way to reduce the carbon footprint of the building”, explain Irene Perez and Jame Mayol, who founded the architectural firm Ted’Arquitectes in Palma de Mallorca (Spain). Both promote the reuse of materials, as do more and more architects.
The construction of a detached house consumes 40 times more resources than renovation, and that of a collective housing building about 80 times more, adds the French Agency for the environment and energy management.
T – RAW EARTH
A worker at work on a building constructed with the rammed earth technique, which consists of compacting wet earth in a formwork, in Lyon in central-eastern France on June 27, 2019 (AFP / ROMAIN LAFABREGUE)
Construction in raw earth, ancestral, is in the midst of a renaissance. And the industry is seeking to develop techniques to consolidate the use of earth concrete.
Among the techniques brought up to date: Rammed earth, compacted and coffered earth, cob (raw earth cut with straw or animal dung), cob (successive layers of rammed cob without a framework).
The earth, an inexpensive and local material, contributes to the regulation of humidity and above all to the smoothing of interior temperatures, especially in the event of a heat wave.
It is found in Canada (Nk’Mip Desert Cultural Center), in the Austrian region of Vorarlberg, or in the form of prefabricated adobe panels, in Lyon in France.
In 2021, the Renzo Piano studio delivered a children’s hospital in Entebbe, Uganda, to an Italian NGO, all in rammed earth, made from excavated land, topped with photovoltaic panels.
Workers at work on a building constructed with the rammed earth technique, which consists of compacting wet earth in a formwork, in Lyon in central-eastern France on June 27, 2019 (AFP / ROMAIN LAFABREGUE)
The German-Burkinabe architect Francis Kéré, winner of the prestigious Pritzker Prize in 2022, made construction from local materials, including earth, his trademark, stamped “sustainable high tech”.
U – URBAN PLANNING
Experts recommend slowing down new construction, promoting renovation in the city center, stopping urban sprawl, or even “rebuilding the city on the city”.
V – PHOTOVOLTAIC GLAZING
Glass panels are used to generate electricity from filtered sunlight. Still expensive, this emerging technique foreshadows the connected buildings of tomorrow, but comes up against the shortage of materials, particularly silicon.
© 2022 AFP
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