Sustainability advocates have raised concerns that Australia’s green building criteria are unsuited to the climate zones of many parts of the country, and will thus hamper efforts to raise the energy efficiency of the built environment.

Problems with Australia’s building efficiency criteria were brought to light last year by the winners of the 2014 Australian Institute of Architects Gold Medal, Adrian Welke and Phil Harris of the Northern Territory’s Troppo Architects.

The pair made the point that current criteria are based upon the premise that maximizing the energy efficiency of houses requires sealing them up and stuffing them with insulation instead of exploiting nature design features or enhanced ventilation to achieve more efficient temperature modulation.

Harris noted that many of Troppo’s early houses had received low or zero-star energy ratings despite not spending a single watt of electricity on cooling over the past few decades, and referred to these poor appraisals as being almost a “badge of honour.”

The complaints voiced by Welke and Harris have been at least partially vindicated by a recent CSIRO report for the Department of Industry, which investigated whether or not residential buildings with 5-star energy efficiency ratings under the Nationwide House Energy Rating Scheme (NatHERS) achieved higher levels of efficiency performance.

The CSIRO’s Evaluation of the 5-Star Energy Efficiency Standard for Residential Buildings found that while the 5-star standard did signify a reduction in the level of energy needed to maintain home temperatures in winter, it was also accompanied by higher cooling costs.

This disparity in performance bodes poorly for the application of NatHERS tools to many parts of Australia, given the torrid nature of the country’s climate zones.

“Heating costs were reduced and cooling costs increased in higher-rated houses,” said the report. “The net annual impact was that Brisbane costs were greater in higher-rated houses, whereas Adelaide and Melbourne costs were lower for the higher-rated houses.”

The report also noted that greenhouse gas emissions of higher-rated houses increased in the summer across all cities included in the study, although emission nonetheless fell by seven per cent for the full year.

The reason for the inability of the NatHERS criteria to reflect this disparity in efficiency performance across the seasons is the use of a single rating that is created by adding together both heating and cooling loads.

As a result of this process, a higher rating may not necessarily ensure greater energy efficiency for cooling purposes, which is more important in many parts of Australia due the country’s balmy weather.

If this shortcoming isn’t remedied, then rating systems like NatHERS are likely to become even more disingenuous in future as global climate change results in hotter summers and higher year-round average temperatures and indoor cooling assumes an even greater share of home energy consumption.