The standard is a binding policy instrument that sets a minimum proportion of green spaces in the total area of new development projects in the city of Lyon, France. While the city has 39 percent of green space, only 10 percent is publicly accessible. For greater accessibility to urban green spaces, Lyon has established a standard on the minimum amount of green spaces in new development projects as part of the Local Urbanism and Housing Plan (PLU-H; Plan Local d’Urbanisme et de l’Habitat), which was approved in 2019. The standard represents a constraint to future constructions by defining the minimum area of green space on each piece of land and the required type of greening. The standard was implemented in reaction to the observation that in certain zones of the PLU-H (especially in the city centre and mixed residential zones among others), building permits for construction projects with 'massive' building with insufficient proportion of green spaces for a given site were often proposed. Amendment no. 3 therefore aims to increase the proportion of open green spaces in construction projects in these zones (from 5 to 10% more according to the type of urban zone). The standard is a top-down strategy with potential as it targets the construction sector and sets mandatory requirements for open green space. Thereby it promotes tree planting and the growth of nature in the city.