The Biotope Area Factor establishes that the development of new buildings requires a proportion of the area to be left as a green space. The BAF provides developers, architects and designers with clear but flexible guidelines on the portion of a plot of land that must be planted or provide other green space functions in terms of: improvement of the microclimate, urban cooling, sustainable drainage, improvement of natural habitats and enhancement of the quality of the residential environment. Specific solutions implemented in the BAF included: (i) greening of functional spaces (e.g. bike or bin sheds); (ii) planting trees and shrubs or, in smaller areas, climbing plants to create green walls; (iii) introducing green roofs; (iv) paving only on main routes and using permeable surfaces elsewhere.
These measures reduce radiation fluxes, provide shade, provide cooling effect inside buildings and outside, improve air and water quality, and improve storm-water run-off. The strength of the BAF concept is that it allows flexibility of the site design: the developer may decide what green space measures are applied, and where, as long as the required green space ratio is achieved.
The BAF formula calculates the proportion of an area that needs to be green space: BAF = Ecologically Effective Surface Areas/Total Land Area. BAF targets depend on the specific uses of an area. Residential and public areas need to achieve a BAF target of 0.6 while commercial, business and administrative areas are requested to achieve a lower target of 0.30. Different types of green spaces are weighted differently according to their “ecological value”, based on evapotranspiration capacity, permeability, possibility to store rain water, relationship to soil functioning and provision of habitat for plants and animals. For example, the weighting of surfaces with vegetation unconnected to soil below is 0.5; that of surfaces with vegetation connected to soil below is 1.0 and that of green roofs is 0.7. The developers can thus use a wide range of options combining different areas with different types of surfaces for achieving the required standard.