Oslo and neighbouring Bærum municipalities participated in developing the first version of Blue-Green Factor (BGF) in 2014. Since then the BGF became a city norm in 2019 and has been further developed into a national Norwegian Standard aimed at all municipalities in Norway. The BGF norm is a performance-based green area indicator aiming to ensure sufficient vegetation cover and surface water management in individual residential development projects. A list of outdoor blue and green surfaces and structures - i.e. nature-based solutions - are scored qualitatively, scaled by surface area, with the weighted sum divided by the total area of the project computed to a "blue-green factor" (BGF). The factor must be equal to or greater than the norm for the area of the city where the project is located. The current norm weights measures based on stormwater retention, bluegreen structure, biodiversity and recreation and amenities. In Oslo BGF supports Oslo Municipality’s “Strategy for Stormwater Management”, the Green Roof Strategy and the strategic aim of the Oslo Tree Project to plant 100 000 trees in Oslo by 2030. BGF interacts with other policy instruments to promote the feasibility of NBS on private property.