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Green Star rating calculation

Green Star rating tools award points for achievement of specific credits in each rating category, as defined in the applicable Green Star Technical Manual.

The single (overall) score of a project is determined by:

  1. Calculating each category score;
  2. Applying an environmental weighting to each category;
  3. Adding all weighted category scores together; and
  4. Adding any innovation points that may have been achieved.

Category Scores

A project's score is determined for each category based on the percentage of points achieved as follows:

Category Score = No. of Points Achieved / No. of Points Available x 100%

For example, if 8 energy points were achieved out of a total available of 13 then the category score would be 61.5%.

Not all credits are applicable to every project, and many credits have an 'na' option. In these instances, the points for these credits are excluded from the 'Points Available' used to calculate the category score. This prevents distortion of the category scores (up or down) for issues that are not applicable in that project or building.

Example:

A refurbished building will not have new concrete poured and therefore cannot achieve the credit for use of recycled content in structural concrete. In this case, the points are not awarded and the Points Available for this credit are excluded from the Category Score calculation.

Environmental Weightings

An environmental weighting is applied to each category score (except Innovation). This balances the inherent weighting that occurs through the number of points available in any rating category.

The category weightings were derived by considering a variety of scientific and stakeholder input, including:
- The OECD Sustainable Buildings Project Report;
- Australian Greenhouse Office, Environment Australia, CSIRO, the Cooperative Research Centre for Construction, and the Commonwealth Dept. of Environment and Heritage; and
- A national survey conducted by the Green Building Council, which informed the development of the tool and assisted in assessing regional variation.

Weightings also vary by geographical location, to reflect issues of importance in each state or territory. For instance, potable water has a greater significance in South Australia than the Northern Territories, and therefore the Water category has a higher weighting in South Australia.

The weighted category score is calculated as follows:

Weighted Category Score = Category Score (%) x Weighting Factor (%) / 100

Using the same example from the Category Score above, the Weighted Category Score would be: (61.5x 25 / 100) = 15.3


Single Score

The single (overall) score is determined by adding together all the weighted category scores plus any innovation points (which are not weighted) that may have been awarded. The maximum possible score for the weighted categories is 100 with an additional 5 points available for innovation.
Single Score Rating

The Green Star rating is determined by comparing the overall score with the rating scale shown below.

One Star 10 - 19 pts
Two Star 20 - 29 pts
Three Star 30 - 44 pts
Four Star 45 - 59 pts Best Practice
Five Star 60 - 74 pts Australian Excellence
Six Star 75+ pts World Leadership

The Green Building Council of Australia only certifies buildings that achieve a rating of Four, Five or Six Stars.