In order to normalise assessments between building types the environmental and cost impacts are expressed in terms of an applicable functional unit.  Typically eTool uses the following functional units for different project types:

• Commercial Office – Impacts measured at:
  • Per m² per year (generally Net Lettable Area is preferred); or
  • Per Occupant Hour
• Residential buildings – Impacts measured at:
  • Per occupant per year
• Community, healthcare, retail – Impacts measured at:
  • Per m² per year (generally Net Lettable Area is preferred); or
  • Per Occupant Hour
• Industrial buildings – Impacts measured at:
  • Per m² per year (generally Net Lettable Area is preferred)

All the functional units rely on a prediction of design life, which has a very large effect on their comparable sustainability. Although difficult to predict, eTool uses a methodology aimed at producing fair and repeatable comparisons between building designs. Individual building life spans will deviate significantly from the design lives calculated using this methodology, however the aim is to predict the mean expected life of all buildings with similar characteristics and circumstances. You can read about it in detail here.