The 2022 National Construction Code brought the most significant changes to residential energy efficiency requirements in over a decade. The minimum NatHERS star rating for new Class 1 buildings increased from 6 stars to 7 stars, and new whole-of-home energy budgets were introduced that account for the energy used by heating, cooling, hot water, lighting, and on-site energy generation.

For architects and designers, these changes fundamentally shift how early-stage decisions need to be made. The building envelope, the mechanical system type, and the glazing strategy are no longer independent design decisions — they’re an interconnected energy system that needs to be modelled together from the start.

What Changed in NCC 2022

The star rating minimum increased

Class 1 buildings (detached houses and townhouses) now require a minimum 7-star NatHERS rating, up from 6 stars. The NatHERS scale is not linear — the difference between 6 and 7 stars represents a meaningful reduction in predicted annual energy load, and it requires deliberate design decisions to achieve consistently.

Whole-of-home budgets were introduced

Alongside the star rating, the 2022 NCC introduced a whole-of-home energy budget that puts a cap on total annual energy consumption of fixed appliances — heating, cooling, water heating, pool and spa equipment, and artificial lighting. On-site generation through solar PV can offset this budget, but the budget itself must be met.

The deemed-to-satisfy provisions tightened

For projects using the DTS pathway rather than NatHERS modelling, the insulation requirements, glazing performance specifications, and shading requirements all became more stringent. If you’re not using full NatHERS modelling, your default specifications just got harder to meet.

What This Means for Design

Glazing decisions have larger consequences. Large areas of west or north-facing unshaded glazing were already a risk factor for NatHERS ratings — they’re a bigger risk now. The higher star rating minimum means there’s less headroom to absorb poor solar control decisions elsewhere in the design.

Mechanical system selection is part of the energy equation. The whole-of-home energy budget is affected by what heating and cooling system is specified. An all-electric heat pump system has a different energy budget impact than a gas ducted system. In some cases, specifying a more efficient mechanical system is the most cost-effective way to improve an NatHERS outcome — more cost-effective than adding insulation or changing glazing.

Orientation and massing matter more. Buildings with poor solar orientation have less room for error everywhere else. If site constraints produce a difficult orientation, that needs to be flagged at concept stage — before windows are sized and positioned.

The Whole-of-Home Budget in Practice

The whole-of-home energy budget is calculated in MJ/m²/year and sets a maximum annual energy consumption for fixed appliances based on climate zone, floor area, and the number of bedrooms. To meet the budget, designers need to:

1. Know the budget number early. Your NatHERS assessor can calculate the allowable budget once floor area and location are confirmed. This should happen at concept stage.
2. Select mechanical systems that are budget-efficient. Reverse-cycle heat pumps for both space conditioning and hot water are the most common path to meeting the whole-of-home budget. Gas systems are increasingly difficult to reconcile in a whole-of-home budget context.
3. Account for on-site generation. A solar PV system can offset the energy budget — but the capacity required depends on the appliance loads, which depend on the mechanical specification. Another reason to resolve the mechanical strategy early.
4. Model the interactions. The star rating and the whole-of-home budget interact. A building that achieves a high star rating with an efficient envelope may have more budget headroom for appliances.

How to Avoid Compliance Surprises

Engage your NatHERS assessor at concept stage, not documentation stage. The assessor can model different envelope and mechanical configurations before anything is committed. This is when modelling is most valuable — and least expensive.

Engage your mechanical consultant at the same time. The mechanical system type needs to be a design decision, not a specification decision. It affects the NatHERS model, the whole-of-home budget, the structural requirements, and the architectural intent.

Don’t rely on default values. NatHERS software allows the use of default values for unspecified building elements. A rating produced with default values will not match a rating produced with actual specified values, and the difference is often significant enough to affect compliance.

Working With Air Theory on NatHERS

Air Theory works alongside NatHERS assessors and architects from concept stage to ensure mechanical design decisions are aligned with energy performance targets from the start. Our involvement typically includes providing system type recommendations for use in NatHERS modelling, reviewing modelling assumptions to ensure they reflect the intended mechanical design, and documenting the final mechanical specification in a way that supports the final NatHERS certificate.

For projects targeting Passive House certification or passive-standard performance, we also provide thermal modelling and airtightness strategy as part of our Passive House consulting add-on.

If NatHERS compliance is a concern on your next project, get in touch — it’s a much easier conversation to have early.