“7-Star Energy Efficient”: Misleading Sustainability Claim?

In today’s property market, it’s common to see homes advertised as “6-star” or “7-star energy efficient” (see just a few examples from a popular real estate listing website below). These labels, while technically compliant with minimum National Construction Code (NCC) requirements, are often used to imply superior sustainability or thermal comfort. The reality is very different.

At HONE, we believe minimum compliance shouldn’t be confused with best practice. True energy performance is measured not in theoretical star ratings, but in real-world results—comfort, durability and energy use over time. That’s why we build to Passivhaus standards, the global benchmark for high-performance homes.

Understanding the Minimum Standard

In May 2024, the National Construction Code (NCC) update made it mandatory for all new homes in Victoria to achieve a minimum 7-star energy rating under the Nationwide House Energy Rating Scheme (NatHERS). This increase from the previous 6-star requirement is part of a commendable broader national effort to reduce residential energy demand and improve comfort outcomes. While it’s a step in the right direction, it’s important to understand what a 7-star NatHERS rating actually means—and what it doesn’t.

NatHERS is a government-run software-based assessment tool that models a home’s thermal performance based on its design. The rating (0 to 10 stars) estimates the amount of heating and cooling energy required to maintain comfortable indoor temperatures throughout the year. A higher star rating implies less energy needed to achieve comfort, with 10 stars representing a home that theoretically requires no active heating or cooling.

However, NatHERS has major limitations:

• It assesses design intent, not as-built performance. There is no requirement to verify that the home was built to the thermal specifications in the modelling.
• It assumes standardised occupant behaviour, such as window usage and thermostat settings, which may not reflect how people actually use their homes.
• It uses historical climate data, which does not account for worsening climate volatility or urban heat island effects.
• It completely omits airtightness and ventilation strategy, both of which are essential to actual comfort and energy use.

Most critically, NatHERS compliance is often treated as a box-ticking exercise during the design approval phase, with little to no oversight during construction. This creates a significant performance gap between what was promised in documentation and how the home performs in real life.

What Makes Passivhaus Different

Passivhaus isn’t a theoretical model—it’s a proven performance standard, built on five key principles:

• Continuous Insulation to eliminate thermal bridges.
• Airtight Construction verified with blower door testing.
• Triple-Glazed, High-Spec Windows for thermal comfort and efficiency.
• Mechanical Ventilation with Heat Recovery (MVHR) for fresh air without energy loss.
• Rigorous Certification to ensure the building performs exactly as designed.

Passivhaus homes typically use up to 90% less energy for heating and cooling than standard construction.

Melbourne’s Climate Demands More

With hot, dry summers and cold, damp winters, Melbourne requires homes that can perform across extremes. A Passivhaus home maintains stable, healthy indoor temperatures year-round—without relying on gas heating or overworked air conditioners.

What Buyers Should Ask

If you’re evaluating the energy efficiency of a home, go beyond the star rating:

• Has the home been tested for airtightness?
• What insulation strategy was used, and is it verifiable?
• Is mechanical ventilation with heat recovery included?
• What are the measured heating and cooling loads?

Don’t Settle for the Minimum

At HONE, we don’t build to minimum standards—we build for the future. Passivhaus isn’t just a better home; it’s a smarter, healthier and more sustainable investment.

Don’t be misled by marketing spin. Ask the right questions, seek verifiable performance and choose a home that delivers on its promises.