Homes billed as seven-star comfort turn out to be ‘closer to a tent’

A seven-star energy-efficient home built today is designed based on outdated weather data, and as the climate warms, will only provide the comfort of a tent by 2070.

Home buyers could be locking themselves into paying more to heat and cool their homes than they would if the designs were up to date.

All new homes must meet minimum standards for energy efficiency, measuring how much energy is needed to heat and cool them, known as the Nationwide House Energy Rating Scheme (NatHERS).

But the scheme uses weather data from 1990-2015, as of its most recent update two years ago, which is already out of date, new research by advocacy organisation Sweltering Cities and sustainability not-for-profit Renew found. The years since were some of the hottest on record.

As the climate warms, the amount of energy needed to cool homes annually will double by 2050, the report Future Climate Impacts on Home Energy Standards found. This means a home that appears efficient today would no longer perform well in future, and would have a lower star rating.

Experts called on governments to update the data so that homes fit for future purpose can be built while reducing emissions and pressure on the energy grid.

The research modelled the energy use of new and older homes in Brisbane, Cairns, Melbourne and Adelaide from 2030 to 2090 using three climate scenario projections.

It found that the amount of energy needed to cool a home in Brisbane was set to more than double by 2050. Its seven-star rating would be almost halved to a rating closer to a tent than a home, under a moderate climate scenario by 2070. The rating falls to zero stars in Brisbane and Cairns by 2090 under a high-emissions climate scenario.

Even in cooler Melbourne, the annual energy required to cool a house would almost double by 2070 under a moderate climate scenario. But a new home’s rating would be little changed as the home moves to using more cooling than heating in a warmer climate.

Sweltering Cities executive director Emma Bacon also warned of the risk to Sydney, as heatwaves – the deadliest environmental disaster – increase in frequency and severity.

“Anyone who lives in western Sydney will tell you they’re facing long, hot and humid summers,” Bacon said.

“Heat is a serious medical risk and often a huge amount of that risk is at home. Being safe at home is one of the most important things we can do, especially low-income communities, multicultural, and people with disabilities.”

She said unless the data was updated, the government was building the next generation of homes that would perform as inefficiently as older homes today.

“People will be using more energy to maintain a safe temperature,” Bacon said.

Not only would it keep people safer but help the country reduce its carbon emissions, she said.

It comes as the federal government aims to deliver 1.2 million new homes in the next five years and improve housing affordability.

Rob McLeod, policy and advocacy manager at non-profit Renew, said Australia was building the next generation of zero-star rating homes unless the weather data used in NatHERS was updated.

“We looked at how hot [a home] would get without an air conditioner. A home that is built today at seven-star ratings will have the same temperature during a hot summer day in 2070 as one of those 1.1-star rental homes does today,” McLeod said.

“If you think about those homes, they’re closer to a tent than a current rating of seven stars,” he said. “We’re building homes that are fit for a 1990s climate but that climate looks very different to the climate we’re facing in the decades ahead.”

He said updating the weather data would ensure new homes were fit for purpose in future and help avoid blackouts during heatwaves.

McLeod said building energy-efficient homes was a cheaper way to improve the star rating than retrofitting.

UNSW researcher and lecturer Dr Anir Upadhyay worked on a similar report for the Western Sydney Regional Organisation of Councils, which found cities on Sydney’s western edge were particularly exposed to the shortcomings of the NatHERS rating system.

Because western Sydney was a growth area, it was more likely to have newer homes built to the seven-star standard, Upadhyay said.

“It is very concerning because the houses where we’re building more aren’t taking into account this warming climate scenario,” he said. “What it really means is that [new homes] won’t respond to the warming situation. During a heatwave, they would not perform well.”

Upadhyay said it would also mean that homeowners would pay more to heat or cool their homes than they would if the rating system correctly took today’s climate into account.

The poorly performing NatHERS system also had implications for Australia’s emissions reduction ambitions, Upadhyay said.

A spokesperson for the Department of Climate Change, Energy, the Environment and Water said it was reviewing the issues raised in the report.

“The department works closely with CSIRO and other research partners to ensure the climate and technical data underpinning NatHERS is as accurate as possible,” the spokesperson said.