Rehabilitating housing to pollute less, the bright future of the old

► “Hybrid and reversible buildings to facilitate their rehabilitation”

Patrick Rubin, architect and founder of the Canal agency, in Paris

“As soon as a building holds up, it has to have several lives. During the second half of the 20th century, rehabilitation focused on beautiful brick, stone and cast iron buildings, most often turning them into cultural venues or chic private spaces.

In recent years, there has been an interest in ordinary constructions, often quickly built with less noble and durable materials. Destroying them is very violent for the inhabitants who have lived there. The potential is enormous, even if it is not always simple. Architecture students are not trained in rehabilitation, because their teachers, also architects, come from new construction.

You have to deal with costs that are sometimes higher than for demolition-reconstruction. In thermal sieves, the materials often have to be changed. Not to mention the asbestos and lead… To transform a 1950s office into a home, the floors are so wide that you have to create interior courtyards to let the light in, which loses a third of the surface.

Eventually, rehabilitation costs should become attractive with the increase in the price of new materials, but above all thanks to the move towards easily reversible hybrid buildings. This is what we obtained in Bordeaux, in the station district, with the first building permit for a building that can accommodate offices and/or housing. It’s new, but when the functions evolve, no more than 30% of the value of the building will be spent on its rehabilitation. »

► “Who knows their apartment better than its occupant? »

Elise Giordano, architect and founder of Atelier Aïno, in Marseille

“Many young architects, inspired like us by Patrick Bouchain (2019 urban planning grand prize) or the Lacaton & Vassal agency (2021 Pritzker Prize), are interested in “rehabilitation”, because it gives meaning to the practice architectural.

Unlike new construction, there is no systematic recipe for rehabilitation, it is case by case. It is first necessary to make the diagnosis of the building, its constructive system, the materials and their state, the context in which it is located. Then comes the discussion with the client to determine his real needs, which are not necessarily those of the program he has set.

For certain projects, such as that of a tower in the 13th arrondissement of Paris, built in the 1960s and rehabilitated as an occupied site, we consulted the residents. Who knows their apartment better than its occupant? We had added functions, such as indoor planters, which had not aroused the enthusiasm of the inhabitants, preferring to keep the layout flexible.

Rehabilitation involves more constraints than new, it’s like an architectural Tetris (puzzle video game, editor’s note). You have to go and see where the electrical networks, the plumbing go… This takes time, know-how and therefore money. However, we are not fighting on equal terms, because the cost of deconstruction and waste are for the moment almost zero, even if this should change with the new anti-waste law. »

► “The quality of use of a building is its true wealth”

Eric Puzenat, associate architect of Ateliers 2/3/4/, in Paris

“Before the need for spaces outside the housing was glaringly felt with the health crisis and the successive confinements, we carried out a transformation of a residence from the 1960s, in Ville-d’Avray (Hauts-de-France). -Seine). The client wanted to rehabilitate them by improving their thermal and energy performance.

From the moment we reflected on the envelope, we could attribute another image to it. We have therefore added terraces in the form of loggias in order to extend the living rooms on the north side, which makes it possible to be in the shade in the summer and to recover the sun in the morning in the winter. Arranged in staggered rows in order to erase the repetitive side of the initial facade and to create plays of shadows, these terraces are self-supporting, thus preserving the external insulation which runs over the entire facade.

We have also redesigned the ground floor by making the entrance more welcoming and accessible to people with reduced mobility. Without being spectacular, this project shows how rehabilitation leads to questioning the quality of use of a building, its true wealth. »

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Reduce greenhouse gas emissions

One and a half tonnes of CO2 equivalent is emitted, for fifty years, the typical lifespan of a building, to build a new square meter, of which 20% for the superstructure and the foundations. This saves at least 250 kg of CO2 equivalent during a retrofit. Depending on the type of rehabilitation, additional emission reductions are possible on the technical lots (15% of emissions) and the facade (5%).

Two to three times less carbon emissions are emitted during rehabilitation than during new construction, by adding the emissions linked to the material used and the energy consumed over fifty years.

In 2019, 70% of urban planning authorizations filed in Paris concern the transformation of existing buildings.

Source: Catalog of the exhibition “Conserve, adapt, transmit”, Éditions du Pavillon de l’Arsenal, 416 p., 42 €.

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