Ecological town planning: what French laws and rules apply to vegetalising buildings?

13 June 2017

With Ecological town planning, vegetalising urban buildings has become increasingly important. Besides being what the French want, vegetalising brings dull roofs alive, keeps homes cool in summer, retains rain water and cleans the air. What more could you ask for? A vegetalised roof certainly looks better than tiles or 100% concrete… however few laws exist and the rules remain hazy. To clear the ground we talked to Tarvel development manager Luc Proton!

Also see: Which are France’s greenest cities?

What French law says…

Although there is, as yet, no law about vegetation on ordinary buildings, the French law on developing biodiversity (1) touches on the subject as an adding to article 111-18-1 of the French town planning code (2). What exactly does it say? That all commercial buildings having presented a request for planning permission after March 1st, 2017 (yes, quite recent!) are obliged to install, at least on part of their roof:

  • either a renewable energy production process (like photovoltaic panels) 
  • or a vegetalisation system guaranteeing effective cooling in summer, building insulation and that supports and promotes biodiversity.

However you do not need planning permission to vegetalise a building. Indeed, the French Grenelle 2 law dated July 12th, 2010 (3) states that no town planning document can prevent the installation of any device designed to retain rain water or limit greenhouse gas emissions. So even if some building permits prohibit flat roofs, they do not prevent vegetalising.

What the Ecological town planning pros say…

New standards are emerging, particularly concerning the plants to be used. Vegetalised roofs must contribute effectively to overall building insulation – and plant root systems must not harm roof weatherproofing!

To ensure perfect building weatherproofing, there are also technical standards indicating the good practice to follow when installing vegetalisation supports on elevations or as covers on roofs. These are called Unified Technical Documents for buildings (DTU)… But when executing a vegetalisation project, there are several pitfalls to avoid! Lastly, the Unep recently prepared some professional guidelines (4) to assist professionals and other technicians throughout every step in building and servicing vegetalised buildings. They evoke in particular vegetalising on timber frames and vegetalising with climbing plants and the greening of roofs… Even if these rules are not obligatory, it is always good to be familiar with them!

Green walls in landscape planning – a fast-growing trend!

It is true that laws and standards do not flower as quickly as vegetalised buildings but those that do exist already show the way for the first steps in Ecological town planning and the greening of urban buildings… Now it’s up to you!

Our thanks to Luc Proton for answering our questions on this subject.

(1) Legifrance, Loi pour la reconquête de la biodiversité, de la nature et des paysages (Law for the reconquest of biodiversity, nature and landscapes) section 9, article 86
(2) Legifrance, Code de l’urbanisme, (Town Planning Code) article 111-18-1
(3) Le Moniteur, Oui aux toitures végétales, même quand le PLU dit non ! (Yes to vegetalised roofs, even if Building Permits say No!)
(4) Les Entreprises du Paysage, Communiqué de presse (Press release)

© Photo credit: Unsplash / Chris Barbalis

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