Creating a productive green roof with Nidaroof panels – integrated water reservoir & stormwater regulation
The City of Paris transformed the rooftop of an annex building of the Hôtel de Ville (a former Napoleonic barracks) into a 1,000 m² edible garden, designed to grow strawberries, radishes, mesclun and even grapevines.
At the heart of this innovative project lies the Nidaplast Nidaroof system, a honeycomb structure enabling the creation of a suspended artificial water table, storing rainwater directly beneath the substrate.
1000 m2
developed surface
100L/m2
designed water storage capacity
2016
year of completion
Project Context and Challenges
Greening urban roofs and producing food locally
In its call for projects, the City of Paris aimed to:
- green urban rooftops,
- create a local, short-supply-chain production area,
- enhance an unused roof surface,
- install an autonomous irrigation system fed by rainwater,
- reduce stormwater load on the sewer network.
The project also supported broader objectives:
- reducing urban heat islands,
- implementing parcel-based stormwater management (EU Water Framework Directive),
- re-naturalising urban buildings.
Objectives Defined by the Project Owner
The specifications required a solution capable of:
- temporary storage of stormwater directly on the roof,
- creating an artificial water table feeding crops by capillarity,
- compatibility with a productive garden (vegetable crops + vines),
- high mechanical resistance ensuring full waterproofing safety,
- delivering a durable and accessible installation.
Solution Implemented with Nidaplast
Nidaroof panels: honeycomb slabs for rooftop stormwater regulation (blue roof / green roof)
The solution relies on Nidaroof honeycomb panels, engineered to retain water in their cells and regulate heavy rainfall events naturally.
They form a structured water reservoir ideal for productive green roofs.
System installed:
- Geoflow 44-1F drainage grid placed on the existing waterproofing,
- Nidaroof panels (50 mm cells – 95% void ratio) acting as the reservoir,
- Filter geotextile layer supporting the substrate,
- Special agricultural substrate, partly installed in a “lasagna-type” layering,
- Overflow outlets for excess water management.
Advantages in this context:
- Creation of a suspended artificial water table without pumps,
- 100 L/m² water storage enabling natural irrigation of the garden,
- Delayed and reduced stormwater discharge to sewers,
- Contribution to reducing heat islands,
- Lightweight and modular honeycomb structure (SAUL technology),
- Durable, resistant material partially made from recycled content — compatible with food production on roofs.
Technical Characteristics of the Installed Product
Panel dimensions:
2400 x 1200 mm.
Panel height:
100 mm.
Permeability:
≥ 90 %.
Material:
extruded polypropylene
Geotextle :
face 1 : PET 150g/m2 - face 2 : PET 25g/m2
Nidaroof
Honeycomb panels for temporary storage and retention of rainwater on flat roofs and roof terraces.
View product sheetInstallation Process
1. Surface preparation
Structural analysis and inspection of the two-layer waterproofing (excellent condition, no repair required).
2. Laying the Nidaroof panels
Installation of the Geoflow drainage grid, followed by Nidaroof panels over the entire area.
3. Filling and finishing
Installation of the filter geotextile, then the two types of substrate (vegetable garden & vineyard areas).
Planting of strawberries, radishes, mesclun, herbs, nasturtiums (west section) and preparation of the vineyard plot (east section).
Water filling, infiltration tests and verification of the proper functioning of the artificial water table.
Watch the installation video
Results and Benefits Observed
Fully functional, autonomous artificial water table
Regulation of heavy rainfall and reduced discharge to sewer networks
No excessive structural load — suitable for lightweight roofs
Active contribution to Paris greening and heat-island mitigation
Roof transformed into an ecological, productive and accessible space
« With Nidaroof, we were able to create a natural water reserve beneath the garden while regulating rainfall and turning this rooftop into a truly productive ecosystem. »
— Project managers – Groupe Loiseleur / Urbagri / Siplast
