Why 7-Star Energy Efficient Isn’t the Sustainability Benchmark You Might Think It Is

Why minimum compliance rarely delivers real comfort or resilience

Australia’s 7-Star energy efficiency requirement has improved the baseline quality of new housing. It is a step forward from earlier standards and has raised awareness of thermal performance.

However, compliance with a minimum rating is often mistaken for sustainability. In practice, many 7-Star homes still struggle with comfort, high energy use and poor summer performance.

This is not because the rating system is flawed, but because it was never intended to guarantee real-world outcomes.

What a 7-Star rating actually measures

The 7-Star NatHERS rating is a thermal modelling tool. It estimates the amount of energy required to heat and cool a home under standardised assumptions.

It does not:

• Measure airtightness
• Verify construction quality
• Test delivered performance
• Account for future climate extremes
• Ensure indoor air quality or moisture control

The rating describes potential thermal performance under idealised conditions. It does not confirm how the home will actually behave once built and occupied.

For a clearer explanation of the fundamentals that sit behind these ratings, see Building Physics Made Simple.

Where the gap appears

The gap between compliance and lived performance usually opens during construction.

Small deviations accumulate:

• Incomplete insulation
• Thermal bridges at junctions
• Uncontrolled air leakage
• Substituted materials
• Poorly sealed services and penetrations

None of these issues necessarily prevent a home from achieving a 7-Star rating on paper. All of them undermine comfort, energy efficiency and durability in practice.

This is why compliance should be viewed as a starting point, not a benchmark.

Airtightness is not addressed by 7-Star

One of the most significant omissions in minimum compliance is airtightness.

Uncontrolled air leakage has a major impact on:

• Heating and cooling demand
• Drafts and uneven temperatures
• Summer heat gain
• Moisture movement within the building fabric

Because airtightness is not measured or tested under 7-Star, it is often overlooked entirely.

High-performance frameworks such as Passivhaus (Passive House) treat airtightness as a core construction outcome, verified through testing rather than assumed. This difference alone explains many of the performance gaps seen between compliant homes and genuinely comfortable ones.

For a construction-focused explanation, see The Airtight Case for Passivhaus.

Summer comfort and overheating

Another limitation of minimum compliance is how it addresses summer conditions.

Many compliant homes perform adequately in winter but overheat during extended warm periods. This is increasingly common as Australian summers become longer and more intense.

Overheating is rarely solved by higher star ratings alone. It depends on:

• Limiting heat gains
• Controlling air movement
• Managing thermal mass
• Allowing effective night-time cooling

These outcomes are heavily influenced by construction execution.

This issue is explored in more detail in Designing for Overheating in a Warming Climate.

Sustainability is more than operational energy

Energy efficiency is only one component of sustainability.

A truly sustainable home must also consider:

• Durability and service life
• Indoor air quality and occupant health
• Adaptability to future climate conditions
• Construction waste and material use

A home that meets minimum energy standards but requires frequent intervention, excessive cooling or early refurbishment cannot be considered sustainable in any meaningful sense.

Why higher standards focus on delivery, not just modelling

Performance-led standards place greater emphasis on:

• Buildability
• Quality assurance
• Testing and verification

Passivhaus, for example, requires airtightness testing and performance modelling that accounts for real climate conditions. This shifts the focus from theoretical compliance to delivered outcomes.

Whether or not Passivhaus is pursued, the underlying lesson is clear: sustainability depends on how a home is built, not just how it is rated.

For context on how this applies locally, see Does Passivhaus Work in Australia?

Compliance is the floor, not the ceiling

Minimum standards exist to lift the baseline. They are not designed to deliver best practice outcomes.

Treating 7-Star as a sustainability benchmark sets expectations too low for the climate conditions Australian homes now face. Comfort, resilience and long-term performance require a deeper understanding of building physics and disciplined construction delivery.

At HONE, compliance is treated as a starting point. The focus is on delivering homes that perform reliably in use, not just on paper.