Energy Ratings


All Australian States and Territories require new homes to meet minimum thermal performance standards. The overall regulation requiring Building Thermal Performance Assessment ratings is the Building Code of Australia (BCA), applicable in all states except NSW, where BASIX is the regulation in force

House Energy Rating Schemes (HERS) in Australia such as the Nationwide House Energy Rating Scheme (NatHERS) have traditionally only assessed the thermal performance of residential buildings. HERS tools calculate the heat energy gains and losses associated with the design of the building in a particular location, and determine how much artificial heating and cooling may be required to maintain human thermal comfort. NatHERS is managed by the Department of the Environment, Water, Heritage and the Arts. HERS software accredited under NatHERS can be used to assess compliance with the BCA and other regulations.

Currently available HERS do not include the energy use of appliances or the embodied energy of building materials, although work is underway to broaden Australian HERS tools to cover other energy impacts such as lighting, hot water, and major fixed appliances.

The actual amount of gas or electricity used for artificial heating and cooling is influenced by the behaviour of the occupants and efficiency of appliances, in addition to the thermal performance of the building.

HERS tools are typically computer based due to the millions of individual calculations necessary. Shorthand scorecards have been trialed in Australia but do not have sufficient rigor or sophistication to provide accurate assessments of environmental performance.

The main software tools in use are:

  • AccuRate.
  • BERS.
  • FirstRate.

These tools are based on a HERS calculation engine developed by CSIRO that enables assessment of a building on an hour by hour basis for a whole year. Included in the calculations are regional climate data and the individual design of the building, as well as thermal properties of all major materials.

To enable comparison of the building performance, distinct from variables such as occupant behaviour, ratings are based on standardised assumptions about the occupation and operation of the building. Performance can be described in terms of heating and cooling loads or degree hours, hours of discomfort or indoor temperatures.

For regulatory purposes, the assessment is often expressed as a star rating. The more stars the better the performance. Star bands are set for each specific climate zone to allow fair comparison of buildings across climates.