Why Your NatHERS Rating Failed (and How to Fix It Fast)
A first-run NatHERS result below 7 stars is normal. These are the usual culprits and the quickest, cheapest ways to lift the rating.
If your first NatHERS result came back under 7 stars, do not panic. It happens on a large share of first runs, and it is almost always fixable without redrawing the home. After thousands of assessments, the same handful of issues come up again and again. Here is how to diagnose and fix them.
The usual suspects
- Too much unshaded west glass. West-facing windows cop the worst afternoon heat. Oversized or unshaded west glazing is the single most common cause of a low rating.
- Thin or missing insulation. Under-specified ceiling insulation drags the result down quickly.
- Poor orientation. Living areas facing south or west miss free winter sun and gain unwanted summer heat.
- Inadequate eaves. Eaves that are too shallow let summer sun pour into north windows.
- Dark roof in a hot zone. A dark roof in a Western Sydney climate adds cooling load.
The fastest, cheapest fixes
| Fix | Relative cost | Rating impact |
|---|---|---|
| Add or deepen eaves and shading | Low | Medium to high |
| Increase ceiling insulation R-value | Low | High |
| Lighten roof colour | Low | Medium in hot zones |
| Upgrade glazing on worst faces only | Medium | High |
| Resize or relocate windows | Low at design stage | Medium to high |
The order to try them in
Start with the free and cheap levers: shading, insulation and roof colour. Only reach for premium glazing once the easy wins are exhausted, and apply it to the faces that need it rather than the whole home. A good assessor will test these options and tell you which combination reaches 7 stars for the least cost.
Frequently asked questions
Does failing mean a full redesign? Almost never. Targeted upgrades usually close the gap.
How quickly can a re-run be done? Once we know your preferred changes, a re-model is usually same or next day.
Stuck below 7 stars? We can rescue the rating with the most cost-effective changes. Get in touch.
BASIX & NatHERS specialists, a division of Contrive Consultants. We help NSW homeowners and builders achieve energy-efficient, compliant homes.