Green Area Factor and other Tools

WHAT IS Green area Factor ?

The “Green area Factor (GAF)”  is one of the main tools presented in the iWater project. The developed green factor method provides an excellent opportunity to improve the city’s urban planning practices.

The report below “Developing the City of Helsinki Green Factor Method” describes the development process of the City of Helsinki Green Factor method. The objective of the method was to develop a practical tool for use by city planners that is based on research data, takes into account local characteristics and does not discriminate against low-budget projects by favouring expensive ecological solutions. Case studies, stakeholder events and surveys were used to ensure the functionality of the method. The method has been developed on the basis of existing green factor scoring methods while taking into account the climatic, ecological and legislative features specific to Finland and the wishes of those responsible for land-use planning.


The goal of the green factor approach is to mitigate the effects of construction by maintaining a sufficient level of green infrastructure while enhancing the quality of the remaining vegetation. The significance of green surfaces in the adaptation to climate change is highlighted as the city structure becomes denser.


The green factor method improves the city’s prerequisites for adapting to climate change by promoting the green efficiency of the vegetation on the plots and the conservation of sufficient green structure. Vegetation mitigates the risk of flooding, reserves carbon dioxide, cools down the heat islands of built environments and increases the pleasantness and beneficial health-effects of the urban spaces.

In the green factor method, the planner sets a green factor target level for the plot that can be achieved flexibly by the garden designer using various green elements when designing the garden. The method developed for the City of Helsinki provides 43 different green elements relating to planted and maintained vegetation, various run-off water solutions and permeable surfaces, etc. The green factor is calculated as the ratio of the scored green area to lot area.

The green factor method has been developed to support the land use planning process, and it is intended particularly for city planners, landscape architects and garden designers. The green factor can, for example, be included in the zoning regulations or used for granting concessions during a construction permit application process. Similar green factor methods have been used with success in, among others, the cities of Berlin, Malmö, Seattle and Toronto, as an important tool for maintaining and increasing the ecological and social advantages of green structures.

The specific phases of developing the Helsinki Green Factor included:

  1. A comprehensive literature review on relevant topics; interviews and surveys for experts and developers of previous green factor methods
  2. Establishing the list of green factor elements commonly used in urban planning to be included in the tool; calculating weighted scores for each element based on its importance to ecology, functionality, landscape, and maintenance
  3. Developing a land use classification for identifying the correct levels of target and minimum green factor scores; setting specific targets and minimum (required) levels for each land use class while factoring in regional and lot-specific attributes
  4. Creating the Green Factor Tool, a user-friendly Excel interface guiding the user through the green factor calculation
  5. Creating illustrative visualizations of specific green factor levels for the Kuninkaantammi pilot area
  6. Testing the method in the Kuninkaantammi and Jätkäsaari pilot areas (residential blocks); an interactive workshop for testing the Green Factor Tool

The developed green factor method provides an excellent opportunity to improve the city’s urban planning practices in the desired direction because it literally provides a means to “assess and develop alternative ways to build an ecological, climate-proof and dense city in which the social values of urban green areas are a priority 1".

This new method differs from previous green factor methods in that its development has involved more extensive background studies, and expert opinions have been obtained from a range of disciplines. Determining the pilot sites at the beginning of the project has meant that the focus of testing the method has been on residential blocks, which means that in order to finalise the method, extensive testing is still required in areas dedicated to trade, offices or business, services and industrial operations.

Picture: City of Helsinki Environment Centre, Helsinki 2016