French Green Roof and Solar Law (2015)

In March 2015, France approved a law requiring that the rooftops of new buildings in commercial zones be partially covered with vegetation or solar panels. The measure was reported internationally, including by the United Nations Framework Convention on Climate Change secretariat, as a significant national step toward greener roofs.

What it required

• Scope: new buildings in commercial zones across France.
• Options: roofs must be partly covered with plants (a green roof) or with renewable energy production such as solar panels.
• Partial coverage: the law did not require full coverage of every roof, allowing owners to choose between, or combine, vegetation and solar.

Aims

Both options put otherwise unused roof space to work: vegetation for its insulating, rainwater-retention and habitat benefits, and solar panels for renewable electricity.

Checking current rules

The 2015 requirement should be read as a starting point. Building regulations change over time, so the obligations that apply to a specific French project should be checked against the regulations in force when it is permitted.

Comparison with other policies

Unlike Toronto's bylaw, which sets coverage percentages by building size, or Basel's rule, which specifies substrate depth and native plants, the French law framed solar panels and green roofs as alternatives. This made it one of the first national laws to treat rooftop solar and vegetation as interchangeable ways to use roof space.

Practical implications for roofs

The two options place different demands on a building. An extensive green roof adds substrate and plants weighing roughly 50-120 kg/m² when established, and requires a root-resistant waterproofing layer, drainage and maintenance. Solar arrays add less weight in many cases but introduce attachments or ballast, electrical equipment and fire-access considerations. Designers therefore choose between the options based on structure, roof slope, orientation and the owner's priorities.