NatHERS star ratings — how homes earn their stars

What is NatHERS?

The Nationwide House Energy Rating Scheme (NatHERS) rates how well a home’s design and construction — its orientation, walls, roof, insulation, windows and shading — keep it comfortable using the least possible heating and cooling energy (Nationwide House Energy Rating Scheme [NatHERS], 2025). More stars mean a better building shell:

• 0–1 stars — the shell does almost nothing; occupants depend entirely on heaters and air conditioners.
• 6 stars — the minimum standard for most new homes from 2010 to 2022.
• 7 stars — the current minimum for most new homes under the National Construction Code 2022.
• 10 stars — the home barely needs any artificial heating or cooling at all.

Importantly, the stars rate the building, not the occupants: appliances, hot water, lighting and how long you run the air conditioner are not part of the star rating.

How an official rating is produced

Official ratings come from NatHERS-accredited software (AccuRate, FirstRate5, HERO and BERS Pro), all powered by CSIRO’s “Chenath” simulation engine. The software builds a virtual model of the home and simulates its temperature hour by hour across an entire yearof local climate data — 8,760 hours — to work out how much heating and cooling energy would keep it comfortable (CSIRO, 2026). That energy total, adjusted for floor area, is compared against official “star band” tables to assign the stars.

69 climate zones — stars are local

A design that stays cool in Darwin’s humidity would be freezing in a Hobart winter. So NatHERS divides Australia into 69 climate zones, each with its own weather file and its own star band table (NatHERS, 2023, 2025). The stars measure how good a home is for its own climate— a 7-star home in Cairns and a 7-star home in Canberra are equally “good”, but they achieve it with very different designs and energy budgets.

Each star level in each zone is defined by a maximum yearly heating-plus-cooling load, in megajoules per square metre of floor per year (MJ/m²·yr) — the lower the load, the more stars. In zone 1 (Darwin), for example, the band runs from 809 MJ/m²·yr at half a star down to 190 at ten stars (NatHERS, 2023).

The NCC 2022 seven-star rule

The National Construction Code 2022 lifted the minimum standard for most new homes from 6 to 7 stars, and added a second test: separate caps on the heating load and the cooling load, so a home can’t compensate for a terrible summer design with a great winter one (Australian Building Codes Board, 2022). States adopted the rule on different dates — Victoria and Queensland from May 2024, South Australia from October 2024, while NSW applies equivalent requirements through its BASIX system.

What actually earns stars

The star rating rewards classic passive design (Commonwealth of Australia, 2024):

• Orientation — living areas facing north catch winter sun and are easy to shade in summer.
• Insulation — ceiling, wall and floor insulation slow heat moving in and out.
• Windows & glazing — double glazing and the right window sizes; glass is the weakest thermal link.
• Shading — eaves, awnings and trees that block summer sun but admit winter sun.
• Draught sealing — gaps around doors, windows, vents and downlights leak conditioned air.
• Thermal mass — concrete slabs and brick walls that smooth out day–night temperature swings (best in climates with cool nights).
• Cross-ventilation — window placement that lets breezes flush heat out, crucial in the tropics.