City Hall roof terrace garden with “Wateroof”

Alongside various partners of Urbagri, we took part in an unprecedented urban agriculture project set up on an artificial water table on the roof terrace garden of a building in the City of Paris.

Toiture terrasse transforme e en jardin potager

A rooftop vegetable garden on an artificial water table

“Wateroof” solution at the service of a comprehensive water management system

The challenge

In this project, the challenge was a flat roof with a surface area of almost 1,000 m², that had originally been sealed with a double-layer of self-protecting, bituminous waterproofing. This roof, which housed various items of technical equipment and two glazed roofing units in the centre, was now going to accommodate an edible garden. Composed of vegetable plots and a vine, the garden was going to be built on top of an artificial water table, created by building a system for collecting and storing rain water.

Within the framework of the City of Paris’ updated Climate Plan, the City of Paris’ “Livre Bleu” (blue book on water policies) and the City of Paris’ Biodiversity plan, the aim behind the City Hall Vegetable Garden was to:

Actively fight against the climatic phenomenon of heat islands
Reduce the degradation of air quality
Manage rainwater to reduce road runoff and mitigate heavy rainfall
Provide biodiversity solutions by creating links incorporated into the city’s green belts and ecological systems
Optimize the use of surface areas by turning an inaccessible roof into a productive vegetable garden

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The solution

To tackle the site’s technical challenges while respecting the general contractors’ objectives, our suggestion was to install the following products on top of a new reinforced waterproofing system, adapted to the vegetation: Parafor Jardin Silver - from our range of Geoflow geotextiles, on top of which we could then install our Nidaroof honeycomb-shaped panels to contain the substrates and plants.

The water table could then be put to good use across the entire roof surface, making it possible to store large volumes of rainwater which could then be used to water the plants via textile fabrics with a high capillary action. This avoided the use of an electric pump.

The advantage of this solution was also to help humidify the air in periods of hot weather, and therefore to fight against the heat island effect, in particular through the “evapotranspiration” of plants and the evaporation of water from the substrate and the water table.

Roof terrace transformed into a vegetable garden | 1 year later

Roof terrace transformed into a vegetable garden | See the various stages of transformation

Project Highlights

General contractor: Couvertex
Waterproofing companies: Siplast, Urbagri, Nidaplast and Loiseleur
Surface area: 1,000 m²
Site dates: 19 July to 18 October 2016
Products used: Geoflow 44-1F geotextile, Nidaroof honeycomb-shaped panels, Siplast Primer impregnation coating, Parafor Jardin Silver SBS bitumen sheet, treated with a root repellent.