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 are either measured:
      • Per Occupant Hour
      • Per m2 per year
  • Residential buildings: Impacts measured per occupant per year
  • Community, healthcare, retail: Impacts are either measured:
      • Per Occupant Hour
      • Per m2 per year
  • Industrial buildings: Impacts measured per m2 per year

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.

Although studies that quantify the actual life span of buildings are lacking, the reasons for demolition of buildings are quite well documented. Studies conducted in Australia (Kapambwe, Ximenes, F, Vinden, & Keenan, 2009) and the US (Athena Institute, 2004) indicate that less than 10% of buildings are demolished due to reaching the end of their strutural service life. It is other factors that usually dictate service life, namely:

  • Redevelopment for economic reasons (surrounding land has increased in value to the extent that it is more profitable to increase the density or use of the buliding)
  • Redevelopment for aesthetic reasons (the building is no longer in fasion)
  • Fire or other disaster

For this reason the following characteristics are also considered when estimating design life:

  • Building density
  • Density of the surrounding suburb
  • Design quality

Best practice building design attempts to match the durability with the redevelopment potential of the building.

The eTool estimated design lives often differ compared to industry perceptions of building life span. Architects in Australia for example expect detached residential buildings to last over 60 years (Kapambwe, Ximenes, F, Vinden, & Keenan, 2009).

Posted in: eToolLCD Methodology, eToolLCD Software