Inside a NatHERS Assessment, Part 7: From 6.5 to 7 Stars

Inside a NatHERS Assessment · Part 7 of 7

In Part 6 our worked example reached 6.5 stars – just short of the 7-star minimum. This final part shows how an assessor closes the gap with targeted, affordable changes rather than a redesign.

One affordable path to 7 stars

The guidance suggests a single combination of changes that lifts this Melbourne home (Climate Zone 21) from 6.5 to 7 stars, chosen for cost and ease of construction:

• A darker roof colour, increasing solar absorptance. In a heating-dominated climate like Melbourne, a darker roof absorbs more useful winter warmth.
• A darker window frame colour, on the same principle.
• More wall insulation – adding rigid insulation to specific external and retaining walls, and lifting batts from R2.0 to R2.7 on several wall types.
• More floor insulation – lifting the floor batt above the sub-floor from R2.1 to R2.7, and adding rigid insulation under the lower-level slab.
• Removing the lower-level slab edge insulation, which in this climate and design helped rather than hurt.

That last point is the lesson of the whole series: thermal performance is not about adding more of everything. It depends on the climate, the design and how the elements work together, which is why modelling matters.

This is what optimisation looks like

None of these changes alter the look or layout of the home. They are specification choices made on paper, before construction, that turn a near-miss into a comfortable, compliant, lower-running-cost house. Finding the cheapest path to your rating is exactly what a good assessor does for you.

Building or renovating in NSW and want a 7-star result without over-spending? Get a fast, fixed-fee quote from our HERA-registered assessors.

References and resources

This series follows the worked example known as NatHERS Example 3. The official documents below are the authoritative sources. We host backup copies for convenience, but the versions on nathers.gov.au are definitive.

• Modelling guidance (the steps this series follows): nathers.gov.au | local copy
• Example 3 architectural drawings (the plans referred to throughout): nathers.gov.au | local copy
• Example NatHERS certificate samples (what the assessment produces): nathers.gov.au | local copy
• A guide to the NatHERS Certificate: nathers.gov.au | local copy
• NatHERS Assessor Handbook (the full handbook, all chapters): nathers.gov.au | local copy
• NatHERS guidance note: nathers.gov.au | local copy

Always use the latest version. NatHERS documents are updated from time to time. We do not guarantee that the versions referenced or backed up here are the most current. Always confirm the latest release on the NatHERS website before relying on them.

Disclaimer. This series is for education only. Its purpose is to simplify and explain the official notes where they may not be clear. It is not a substitute for the original documents or for accredited assessor training. If anything is unclear or you have a question, refer to the original document and contact your college or registered training organisation (RTO), or the NatHERS team.

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