NatHERS 7 star envelope vs whole of home: the two parts of NCC sustainability

What it is

The current NCC residential energy standard has two parts that builders often confuse. The first part is the thermal envelope rating, expressed as a star score from 0 to 10 under the Nationwide House Energy Rating Scheme, known as NatHERS. The second part is the Whole of Home rating, a separate score out of 100 that covers the energy used by fixed appliances together with any solar or battery on site. A new Class 1 dwelling has to meet both to get sign off in most states.

NatHERS measures the building shell. Whole of Home measures what runs inside it. The two scores are independent and they fail or pass independently. A builder can design a tight 7 star envelope and still fail the Whole of Home target if the hot water system, the HVAC and the cooktop together blow the annual energy budget.

TradeLens reads thermal assessments, Whole of Home reports, BASIX certificates and Green Star scorecards to flag designs that meet one half of the standard but not the other and contracts that commit to ratings the build cannot deliver.

NatHERS 7 star envelope

NatHERS is a federal scheme that uses accredited software to model the heating and cooling load of a dwelling against the local climate zone. The rating depends on orientation, glazing, insulation, thermal mass and air tightness. The output is a star score, where each star reflects a roughly logarithmic improvement in annual heating and cooling load.

NCC 2022 lifted the minimum thermal performance for new Class 1 buildings to 7 stars. The lift from 6 to 7 stars cuts the heating and cooling load by around 20 to 25 per cent depending on climate zone. NCC 2025 keeps the 7 star floor in place. Building Ministers have confirmed no further residential energy uplift is planned before at least mid 2029.

The rating is performed by a NatHERS accredited assessor using one of the approved software tools, currently AccuRate, BERS Pro and FirstRate5. The output is issued as a NatHERS certificate that the surveyor checks against the approved plans.

Whole of Home budget

The Whole of Home target sits next to the 7 star envelope under NCC 2022 and continues in NCC 2025. It is expressed as an annual energy use budget across heating and cooling, hot water, lighting and pool or spa pumps. A Whole of Home score of 100 represents a net zero operational energy outcome over a year. New Class 1 dwellings have to score at least 60 out of 100 under the national target, though several states have set higher thresholds.

The score is driven by the choice of heating, cooling and hot water equipment, the on site solar PV size and any battery storage. Solar and storage can pull the score up without changing the building shell. A heat pump hot water unit and an efficient reverse cycle air conditioner usually do most of the heavy lifting. A poorly chosen gas instantaneous unit or a resistive electric storage tank pulls the score down fast.

NSW BASIX

NSW does not directly apply the national Whole of Home tool. Instead, BASIX delivers the equivalent outcome through its own water, energy and thermal performance scores. The October 2023 Enhanced BASIX update lifted the thermal performance score to align with the national 7 star uplift and lifted the energy score to broadly mirror the Whole of Home intent.

A new house in NSW therefore has a BASIX certificate that combines thermal and appliance performance into one document. The build has to match the BASIX commitments at occupation or the council can refuse the final occupation step.

Green Star and voluntary tools

Green Star is the voluntary Green Building Council of Australia rating scheme. Green Star Homes scores a home on energy, water, materials, indoor environment and resilience. It sits on top of the NCC minimum and is used by volume builders that want a marketable claim above the legal floor. Other voluntary tools include Passive House for very high performance shells. Almost every project sees NatHERS and Whole of Home, and in NSW the BASIX equivalent.

Where the two scores fail in practice

Three failure patterns turn up. First, a 7 star envelope paired with gas hot water and a resistive cooktop, where the shell passes but the Whole of Home budget fails. Second, a Whole of Home score lifted by oversized solar PV with a thermal envelope that scrapes 6.5 stars, so the envelope fails even when total energy looks good. Third, a BASIX certificate that commits to a heat pump unit and a specific R value, but the as built install uses a different product, so the build no longer matches the certificate at inspection.

How TradeLens uses this

TradeLens flags residential contracts that promise an energy outcome without naming the NatHERS and Whole of Home figures, designs that pass one score while failing the other and as built variations that drift from the BASIX commitment before final inspection.