Why your 7-star energy rating is failing you

Most builders lean on 7-star NatHERS ratings like they’re a gold medal, but usually, they’re just a paper exercise. A 7-star rating is theoretical—it guesses how a design might perform. In the real world, these homes are often failing the people living in them. As a Certified Passive House builder Melbourne families trust, we see the gap between "design" and "reality" every day. It’s for these reasons we can say we are the champions of Sustainable Builders in Melbourne.

The Performance Gap: Design vs. Reality

There is a massive disconnect between what is on paper and what is actually built. Local audits suggest an energy performance gap where as-built homes can use up to 2.5 times more energy than the design predicted.

In Australia, 7-star designs often degrade to 3 or 4-star performance during construction because NatHERS assumes perfect installation. It doesn't account for insulation gaps left by a sparky or thermal bridges where steel frames act as highways for heat. If it isn't tested on-site, the star rating is just a guess.

The Risk of Unventilated Airtightness Recent 2024 data from the CSIRO shows that new Australian homes are finally getting tighter—dropping from the old average of 15.4 ACH down to around 7.0 or 8.0 ACH.

While that sounds like progress, it’s actually creating a new health risk. Builders are making houses tighter to hit energy targets but failing to provide a dedicated source of fresh air. When you increase airtightness without a mechanical pulse like a Heat Recovery Ventilation (HRV) system, you trap moisture and CO2 inside. This isn't high performance; it’s a recipe for sick building syndrome and structural rot.

Carland Construction Proof Point: While the "new" average is roughly 7.5 ACH, our Forrest Certified Passive House (Spotswood) hit a verified 0.41 ACH. That is nearly 20 times more airtight than the current standard. Because we are Passive House specialists Melbourne clients rely on for health, we use continuous mechanical ventilation to swap stale air for fresh, filtered air every few hours.

NatHERS vs. Passive House: What’s the go? NatHERS is a steady-state tool that assumes every house is built perfectly. The Passive House Planning Package (PHPP) is performance-based. It uses actual climate data for your specific block in Melbourne and accounts for every thermal bridge and air leak. It’s the difference between a car’s estimated fuel economy on a sticker and what it actually does when you’re driving it up a hill.

Stop guessing. Demand a Blower Door Test. Without a Blower Door Test, your builder is just wacking it in and hoping for the best. This test is the only way to see if your building envelope actually works.

To reach the gold standard, a home must hit ≤0.6 ACH@50pa. That precision—combined with an HRV system—is what separates high performance homes Melbourne needs from a glorified tent.

The Numbers That Matter:

• Airtightness: New "Tightened" Build (~7.5 ACH) vs. Passive House (≤0.6 ACH).

• Performance Gap: Standard builds often use 2x the predicted energy; Passive House is verified to perform as designed.

• The Health Factor: Standard 7-star builds rely on accidental leaks for air. Energy-efficient homes Melbourne should be building use controlled, filtered, fresh air.

Ready to stop settling for a legal minimum and build a home that actually performs? Contact us to see why we are the Melbourne Passive House construction experts you've been waiting for.