Green Factor: explainer
Get an understanding of the green factor equation and metrics that influence the green factor score.
What is the green factor concept?
The Brisbane Green Factor seeks to measure the quantity and quality of green infrastructure on development proposals. It achieves this through measuring the total amount of green elements, and weighting the value of each against the 6 Ecosystem Service areas. The synthesis of these factors is then measured against the site area to calculate the Green Factor Score.
The basic green factor equation
Green Factor = Green factor area (in m2)/Site land area (in m2)
Because the green factor is relative to a project's size, the score can be used to compare and benchmark urban development projects. This basic equation provides an indication of a project’s composition, with projects that have more green elements - like trees, shrubs, climbers, lawn - likely to score higher.
The following sections provide detail on how the green factor area is calculated.
What influences the green factor area?
The quantity of green elements on a site that might be grouped or located in the ground, or on walls, facades, or roofs will naturally be the key determinant of a project's green factor area. The calculation of each element is however more nuanced.
At a practical level, this calculation:
- rewards certain types of vegetation over others e.g. rewarding native trees over exotic (introduced) trees.
- penalises the removal of existing presumably mature elements. Removed elements that are replaced with new elements will see a smaller penalty (e.g. in the case of trees) that reflects a difference in size between a new and element.
- rewards the retention of presumably mature green elements. This benefit comes from the assumption there is a difference between the size of a new versus mature and retained element (i.e. on consideration of the element’s unit to square metre conversion).
- rewards elements that have more favourable configurations at each location (e.g. elements that are publicly visible and accessible are scored higher than those that are hidden or publicly inaccessible).
- rewards elements that are more desired for their greening efficacy against a set of ecosystem services that have been chosen and prioritised.
The green factor area can be thought of as the sum of its element-level parts. These components are a useful way to step through how the green factor area is determined.
The green factor area equation
Green Factor area
= the sum of
The quantity of a green element
x Unit to sqm (i.e. conversion to an area)
= Equivalent green area (m2)
x Element rating
= Element green factor area (m2)
Like most mathematical equations, it can be more useful to step through a practical example. The Brisbane Green Factor tool features this same equation as an interactive view option for data tables in the green factor scorecard. Council recommends using this to step through this equation for each element in your own assessment to better understand how it works.
Going deeper: How green elements are rated
Understanding the components of the green factor area calculation provides a solid understanding of how a green factor rating is constructed. However, going a step further helps to understand how and why each element may be rated differently in the green factor.
Content team to flesh out further.
Brisbane ecosystem services
| Ecosystem service | Relative weight |
|---|---|
| Food production | 5% |
| Habitat provision | 15% |
| Sense of place | 25% |
| Stormwater management | 20% |
| Urban temperature regulation |
20% |
| Wellbeing and health |
15% |
The result of this process is a table of 1,077 uniquely configured elements that are rated for all ecosystem services within the Brisbane context. All ecosystem ratings are then reviewed.
Content team to flesh out further.
Components of an element rating
Green Factor area
= the sum of
The quantity of a green element
x Unit to sqm (i.e. conversion to an area)
= Equivalent green area (m2)
x Element rating
= Element green factor area (m2)
All of these treatments result in a unitless, index-style element rating that is centred around 1.0, and ranges from about 0.1 to 2.5.
Like most mathematical equations, it can be more useful to step through a practical example. The Brisbane Green Factor tool features this same equation as an interactive view option for data tables in the green factor scorecard. Council recommends using this to step through this equation for each element in your own assessment to better understand how it works.
Learn more about Brisbane Green Factor
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