Every winter, millions of Australians are reminded how hard it is to live comfortably in older homes. Warm air constantly leaks out through poorly insulated ceilings, walls and floors, and through gaps in floors, windows and under doors. Heaters run day and night, sending energy bills soaring.

The gap between new and old homes is huge. Since 2004, new homes across most of Australia have to meet minimum energy performance standards. Homes now have to reach 7 stars on the national Home Energy Rating scheme, known as NatHERS (or the equivalent BASIX system in New South Wales). The higher the rating, the cheaper it is to get through winter or summer.

By contrast, homes built before 2004 get an average of just 2.1 stars. Many lack basic features such as insulation, draught proofing and energy efficient appliances. That’s according to new research we undertook assessing energy performance of almost 1,100 older homes in NSW. Across the state, this means about 850,000 homes would get zero or 1 star for energy performance.

Why does this matter?

Requiring new homes to be more and more energy efficient over time is good policy. Energy efficient homes require less heating and cooling and keep residents comfortable.

But houses last a long time. In NSW, most homes were built before these standards were introduced over 20 years ago. Older homes make up 61% of the state’s housing stock, or just over two million........

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