RESEARCH: Why build homes for a climate that no longer exists?

Sweltering Cities and Renew have released a report laying out how rising temperatures will impact the ‘energy efficiency’ of our homes.

The report shows energy needed to cool homes is set to double by 2050.

The report analyses how changing climate conditions impact Australian home energy efficiency. It explores how the use of historical climate data to set energy efficiency standards in Australia will impact our resilience in rising temperatures and extreme heat.

“Our research finds that the amount of energy needed to cool a home in Brisbane is set to double by 2050. A 7 star home built in Queensland today will score zero stars by 2090 under a severe climate change scenario.” – Rob McLeod, Policy and Advocacy Manager at Renew

You can view the report in detail here.

House Design in Australia

The National Construction Code (NCC) is the regulatory instrument used to set energy efficiency standards across Australia. The NCC is updated every three years with a focus on different areas for consideration. The next update of residential energy efficiency ratings will be in 2028.

Australian building standards require homes to meet energy efficiency standards under the Nationwide House Energy Rating Scheme (NatHERS). The NatHERS ratings measure how much energy is needed to heat and cool homes in a range of climate zones, setting limits for heating and cooling loads to achieve star ratings. The climate zones are designed using existing weather data: until 2022 these were based on weather data from 1970-2005; from 2022 the data is from 1990-2015.

Using out-of-date historical data to set the thresholds of energy efficiency ratings in Australia is resulting in an underestimation of the cooling required to keep homes a safe temperature in summer. There will be higher cooling loads required to keep homes at a safe temperature moving forward. Therefore the star ratings given to new buildings and renovations today underestimate how much energy the home will require, and that difference will grow over time.

“You might think you’re set for the future if you’re building a seven star home, but that rating will go down over time as the actual climate moves further away from the current standard. We need to update the climate data in the National Construction Code to ensure people building today can rely on these regulations to have accurate information for the future.

When the National Health and Climate Strategy was launched by Assistant Minister for Health and Aged Care Ged Kearney in Dubai during last year’s COP, it clearly stated that updating the NCC to make homes safer should be a priority to reduce the health impacts of climate change.” – Emma Bacon, Founder and Executive Director of Sweltering Cities

Report Modelling

Using projected climate data provided by the CSIRO and FirstRate5 software, the report analysed a new home and a poorly performing home in Melbourne, Adelaide, Cairns and Brisbane. Using NCC climate files, as well as CSIRO projected weather files for 2050, 2070 and 2090 (TMY weather files). The findings include:

• Projected changes to energy loads for heating and cooling for each home and climate scenario in the
  years 2030, 2050, 2070, and 2090
• Projected changes to star ratings based on changed energy use
• Simulated indoor temperatures during hot conditions for each case study

Select Report Findings

• Hotter outdoor temperatures increase the internal temperature of homes in all locations and scenarios
• In hotter climates such as Cairns and Brisbane, this increase in temperatures means an overall increase in energy loads
• In cooler climates, reduced heating use offsets increased cooling when calculating total energy use. In the case of Adelaide, a severe climate scenario would see primary home energy use shifting from heating to cooling

Graph: Adelaide scenario shows energy use shifting from heating to cooling in a severe climate scenario (RCP8.5)

• A significant difference was modelled in internal temperatures between new homes (NCC compliant) and older homes and star-rating today does not ensure good performing houses in the future scenarios

Graph: In the case of this scenario, the internal temperatures of a 7-Star home built in 2023 were modelled to be similar (or slightly higher at peak) in 2070 than those of an uninsulated 1.1-Star home under 1990-2015 climate conditions.

These organisations are doing the hard work to enable advocacy through truth-telling data. Climate change mitigation and adaptation with our vulnerable communities is becoming more crucial as they are left most exposed to the health and housing risks of poor housing standards and action on climate change.