They tasted like hell. This summer, the emblematic squares of major French cities heated up so much that they were deserted. From Place Stanislas in Nancy, to Place Bellecour in Lyon, via the Capitole in Toulouse or the Grand-Place in Lille, the majestic esplanades all suffer from the same fault: very mineral, they become unlivable when the temperature rises.
As our climate irreparably warms, municipalities are looking for the right solution to try to “cool” them. » But neither the potted trees tried in Lille and Toulouse, nor the artificial shade houses of Lyon seem effective. To reduce these heat islands, revegetation is obviously the best solution. But it comes up against a multitude of constraints which sometimes make it impossible. Example in Rennes, where the municipality is trying to break up a concrete slab to plant grass. Not easy.
Still in Rennes, the Place de la République is not really one. This large space partly reserved for pedestrians is rather considered the central point of the Breton capital, marking a concrete border between the north and the south. Historically, it was the Vilaine which passed there, sealing the limit between the chic neighborhoods of the north and the common people to the south. For more than a century, the river has been covered to facilitate traffic flows. After much hesitation, the majority of Nathalie Appéré decided to discover part of her river by breaking through a parking lot. But she couldn't do it everywhere.
Break everything to redo everything
Forced to keep a wide passage between the Town Hall Square and the majestic Palais du Commerce, the city chose to plant a lawn there. But for that, he must first break (almost) everything and rebuild. After destroying the old one, pouring a 15-centimeter-thick iron slab, then sealing it with asphalt, the workers will be able to bring in a meter of earth in which they will plant grass. “It’s the minimum if we want to have large lawns,” explains Marc Hervé, first deputy for town planning.
One of the problems with greening is weight. “We need to both repair the structure beneath the square and reinforce it above. The original slab was much too thin to support the weight of the earth and the vegetation,” explains Jean-François Papin, who is leading the operation on behalf of Rennes Métropole. Above the river, it will also be impossible to plant trees, thereby limiting the ability to shade the space. “We would need a lot more earth, we cannot put such a load on the slab. »
Networks hidden everywhere underground
Here, it’s because the river passes underneath. But in many other cases, it is underground parking lots that prevent cities from digging too far, as was the case at Place du Capitole in Toulouse. Or the incredible tangle of water, gas, electricity and fiber optic networks that run beneath the surface. “You can’t imagine everything that passes under our feet. For each tree you want to plant, you have to check everything. Networks, accessibility, structure, impact for traders. And in the perimeter of the old center, the heritage constraints are even stronger,” explains Marc Hervé.
The town planning assistant knows something about this. For years, its services have been negotiating fiercely with the architects of French buildings (ABF) to modify certain emblematic squares. In 2022, the socialist town hall received the agreement to plant 18 oak trees opposite the Town Hall. “The difficulty is not to disturb the facades and the alignments,” explains Marc Hervé. The mayor of Toulouse Jean-Luc Moudenc told us that it was the ABF which had slowed down the installation of a shade “because the facade of the Capitol must be entirely visible. » The Rose City therefore opted for potted trees, which suffer even more from the heat and require regular watering which is not always compatible with the restrictions. In Rennes, lawns will be watered with rainwater pumped from the neighboring metro station.
In 2022, the National Rally deputy Frédéric Falcon also raised “a certain intransigence” among the architects of buildings in France, who “block a number of energy improvement projects. » The urgency was then to protect ourselves from the cold, while the price of electricity and gas had soared. “The architects of French buildings and the heritage services of the ministry are open to projects for greening spaces, while respecting their history and in the interest of their present,” the Ministry of Culture recently promised us.
In addition to all the constraints that we have just cited, we must add the essential one of the desire of municipalities to transform their places. In many cities, these large areas allow the hosting of major cultural or sporting events. “It’s hard to see the funfair being set up around a forest of trees planted in the middle of the Esplanade de Gaulle,” explains Marc Hervé. The Rennes elected official assumes that this large mineral place remains like this. “There always needs to be emptiness in a city. »
