Unsealing a school playground: soil as sponge, soil as cooling system

Why unseal a school playground? To our mind, because a square metre of living ground works for free where a square metre of asphalt only stores heat and sends rain off toward drains that are already struggling, in a downpour just as much as in a heatwave. It holds in a handful of moves: strip out the asphalt where it serves no purpose, plant shade trees, let the water sink in. The ground turns back into the sponge and the cooling system of the place, as we wrote in “Soil first”.

There is a feeling of summer before there is any argument about regulations. A playground shaded by mature trees, ground that holds its coolness instead of handing it back like an oven, means hours of playtime given back to children on the hottest days, when bare asphalt turns hostile and the shadow of a covered walkway is no longer enough. An awning, a shade sail, a classroom air conditioner: all of that gets installed, serviced, replaced. A tree planted in the right spot does the work alone, season after season. It grows up alongside them.

That is the wager we made near Chambéry, in the French Alps, together with POESAGES: three trees and some 300 m² of lawn in place of asphalt, completed in 2024. Under the asphalt, a soil had been waiting decades to breathe again. We stripped out the bitumen wherever it did nothing but store heat, then planted large-canopy shade trees. Rainwater now reaches the ground directly, instead of running off toward a drain. Neither a gadget nor a symbol: three trees and a soil given back to the rain is little enough, and it is already enough to infiltrate, cool and shade without anyone having to think about it. It took very little to change the children’s summer.

This movement is far larger than us. The City of Paris adopted its resilience strategy in September 2017; since then, it has been methodically transforming its school playgrounds: by its own count, 203 oasis playgrounds and 5 oasis crèches were in place by mid-2026, working toward a target of 360 by 2030 under its Climate Plan. The method there is consistent: natural materials, a preference for open ground, trees, green roofs and walls, teaching gardens, even fountains that give water a pedagogical role rather than a purely drainage one. That is the current we work in, at our own scale.

The benefit spills beyond the playground itself: these courtyards are open to the neighbourhood on Saturdays, cool islands offered first to vulnerable residents during heatwaves. An unsealed school playground stops being just a piece of school equipment; it becomes a service rendered to an entire neighbourhood, a few hours a week.

On the ground, the method demands discipline above all. We do not unseal the whole playground. Hard surfacing stays wherever the use demands it: a sports court, accessible routes for people with reduced mobility. The rest, usually most of the surface, goes back to soil. We choose large-canopy species able to cast wide shade without multiplying watering points. We let rain sink in where it falls instead of piping it toward a network that struggles at the first summer storm. Planning law is increasingly pulling the same way: more and more local plans now write in a minimum share of permeable ground, and stormwater zoning, which sets out neighbourhood by neighbourhood how rain is managed, pushes, too, toward infiltrating on site rather than sending water further off. Thresholds vary from one town to the next and have to be read document by document, never taken on faith from a brochure, even ours.

A school playground has line markings, deflated balls, a bell that rings on the hour. Nothing of a manifesto. Perhaps that is exactly why the gesture carries so far: stripping out a few dozen square metres of asphalt, planting a tree that will shade children we do not yet know, letting rain find its way back under our feet. Modestly, without revolutionising anything, we give the place back its own capacity to breathe. How many playgrounds, in your towns, are only waiting for that one gesture?