Climatic and regulatory context

The natural water cycle is altered

As cities expand so do hard surfaces such as roads, rooftops and parking lots. These surfaces create artificially high rate of water runoff, which is extremely difficult for wastewater utilities to manage and results in untreated sewer overflows and rainwater runoff that pollutes local watersheds during heavy rainfall. Expanding traditional grey infrastructure capacity can be extremely expensive and often does not solve the problem. Impermeable ground and increased run off of water in towns have various consequences, which are difficult to control and are expensive for the local authority:

  • Increased risk of flooding and saturation of the drainage network,
  • Added pollution,
  • More phenomena relating to the urban heat island effect


Urbanisation-croissante Torcy71

Secondly, this urban development plays a part in “reducing” Nature and vegetation in the town. Cities are turning to green infrastructure systems such as green roofs to deal with rainwater at the source, and minimize sewer overflow risk and protect water quality.

Technical solutions, referred to as “downstream options”, allow integrated management of rainwater, either by avoiding the creation of impermeable surfaces, or by compensating for its effects. However these solutions have numerous limitations: they are expensive to install and maintain, they often require additional land and do not provide a complete solution for controlling the rainwater entering the drainage networks.

Regulations relating to Managing Rain Water are changing

In 12 July 2010, the Grenelle II law set up a policy for managing water on plots, which was both ambitious and restrictive in terms of controlling waste. Traditional green roofs (solutions known as “upstream options” or “green infrastructure”) provide a partial response to these new constraints. Green roofs capture and hold some of the rainwater, slowing down the speed at which water drains off the roof into the drainage system. However traditional green roofs are not able to control waste draining from the roof (controlling flow rate).

In order to manage rainwater on the plot at source (on the roof), more effort must be made to control and guarantee a consistent flow rate from the green roof, and to increase storage capacity. HydroVentiv® provides this additional control.


Roof runoff coefficient: percentage of rainwater drained away by runoff from the roof. The rest is evaporated or retained by the system.

Instantaneous flow rate from a roof: quantity of rainwater lost by the roof, expressed simply as the unit of time and surface (l/sec/ha).

Laws relating to water

  • Water Law 1992
  • Law on Water and Aquatic Environments (LWAE) of  30 December 2006
  • Grenelle II Law of 12 July 2010 establishes taxation for managing urban rainwater (decree n° 2011-815 of 6 July 2011 which defines and organises the methods of applying the tax.)


As the way traditional vegetated roofs functioned were inadequate in terms of managing rain water, in 2009 the Vegetal i.D. Research & Development department carried out several research programmes in this field.  In partnership with the CETE (Centres d’études techniques de l’Équipement – Equipment Technical Study Centres) IDF (Île de France) and INSA (Institut National des Sciences Appliquées – National Institute of Applied Sciences) Research Centres in Lyon, these programmes led to the development of an innovative and patented solution: HydroVentiv®

Research programmes

The research programmes aimed to:

  • Simulate the fluid behaviour of a vegetating complex and create software to act as a tool to assist with decision-making
  • Produce monthly fluid reports on various vegetated roof complexes (water retention, run-off coefficient, waterproofing coefficient).
  • Develop an innovative solution for controlling water on the roof.


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VEGETAL i.D. designs and produces innovative,useful green solutions that integrate into urban andsuburban environments to make cities more pleasant,environmentally sound and smarter places to live.

A bespoke VEGETAL i.D solution exists for each urban greening project : flat or sloped roofs, biodiverse or biosolar roofs , urban farming , indoor or outdoor living walls , podium decks design with integrated sotrmwater management

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