Aerial view of ancient buildings in Lisbon (Portugal). Old buildings largely «amortized» To meet this challenge, Western countries need to renovate extensively — at a rate of about 10 million homes per year, according to the International Energy Agency. Thedecisiontorenovate isbasedonanumber of factors. These buildings, which have been in use for decades or even centuries, have generally ‘amortized’ the carbon cost of their construction — both in terms of emissions associated with the manufacture of the materials used to create them and those produced during the construction itself. There is no official amortization threshold for a building and the range of 20 to 80 years commonly mentioned is quite wide. The actual duration depends on several factors, such as the quality and durability of materials, maintenance, usage and local weather conditions. Nevertheless, inmost cases, destroying an ‘amortized building’ and replacing it with a new one would lead to a negative energy balance. "For every squaremeter built, 1.5 tons of eqCO2 are emitted for 50 years," says the team at the Pavillon de l'Arsenal, Paris's center for urban planning and architecture, in the book Conserver Adapter Transmettre (Conserving, Adapting and Handing Down).4 "One half comes from materials, the other from energy (…)," they explain. What is the most carbon-heavy element in a construction? The primary structure: the framework and the floors. Conversely, "reusing an existing building can significantly reduce embodied carbon," says Joy Gai, Asia Pacific Programs Head at theWorld Green Building Council (see our article "Operational or embodied: changing perceptions about carbon," page 27). It can generate an estimated saving of 250 kg eqCO2 per square meter. And beyond the carbon cost, "demolishing to rebuild involves more time, more labor, more transportation. By renovating, we can minimize all these items," adds Joy Gai. 4. "Conserver, adapter, transmettre" (Conserving, Adapting and Handing Down) — Éditions du Pavillon de l'Arsenal, 2022 ©EyeEm/Martina 32 SAINT-GOBAIN
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