Reading Your NatHERS Certificate: A Line-by-Line Guide

A NatHERS certificate can look like a wall of numbers and codes, but every line is there for a reason. Once you know what to look for, you can read it with confidence and spot anything that does not match your project.

This guide walks through the main parts of a certificate, explains what each figure means, and shows you how to do a quick sanity-check before you rely on it.

The star rating

The headline figure is the star rating, shown out of ten. It summarises how well the home holds a comfortable temperature with minimal heating and cooling. Under the National Construction Code 2022, new homes in NSW generally need to meet a 7-star whole-of-home thermal benchmark. A higher star rating means less energy is needed to stay comfortable across the year.

It is worth understanding that the star scale is not linear. Moving from 6 to 7 stars represents a meaningful jump in performance, and each additional star above that becomes progressively harder to reach because the home is already efficient. This is why a design that lands comfortably above the benchmark is often a better long-term outcome than one that scrapes in at exactly the required figure, where a small late change could tip it below compliance.

Heating and cooling loads

Below the star rating you will see predicted heating and cooling loads, expressed in megajoules per square metre per year (MJ/m2.year). These two numbers are the engine behind the star rating.

• Heating load is the energy needed to keep the home warm in the cooler months.
• Cooling load is the energy needed to keep it comfortable in the warmer months.
• Total load is the combination, and it maps to the star rating for your climate zone.

A useful habit is to look at the balance between the two. A home with a very high cooling load might need more shading or better glazing, while a high heating load might point to insulation or air-tightness. The split tells a story about where the design is working hard.

For example, a home with a heating load of 90 and a cooling load of 20 is clearly being driven by winter performance, so the design effort belongs in insulation, draught sealing and capturing winter sun. A home with the reverse split is overheating in summer, and the answer is more likely to be shading, lighter-coloured roofing and reduced west-facing glass. Reading the two loads together, rather than fixating on the single star figure, points you straight at the lever that will move the result most.

Climate zone

The certificate names the NatHERS climate zone, which is set by the project postcode. NSW spans many zones, from cool tablelands to warm coastal and hot inland areas. The same house can earn very different ratings in different zones, so always check the zone matches the actual site. If the postcode is wrong, the whole assessment is built on the wrong weather data.

This matters more than it first appears. A design that performs well on the coast may struggle on the cold tablelands because the heating demand is far higher, and the same plan in a hot inland town will be dominated by cooling instead. The certificate is only as accurate as the climate file behind it, so confirming the zone is one of the highest-value checks you can make in a few seconds.

Dwelling and plan references

Every certificate ties back to a specific set of plans. Look for the dwelling description, the address or lot details, and the plan references, including drawing numbers and revision dates. These confirm the certificate was modelled from your current drawings, not an earlier version. This is one of the most common sources of error, so it is worth a careful read.

A practical trap here is the late design change. If a window is enlarged, a room is reoriented or a wall construction is swapped after the assessment was run, the certificate no longer matches the building. Always cross-check the revision number on the certificate against the revision number on the drawings sitting in front of the builder, and treat any mismatch as a stop-and-check moment.

Assessor and software details

A valid certificate records who produced it and how.

• The assessor name and accreditation number, showing they are registered with an accrediting body.
• The assessing organisation.
• The software and version used to run the simulation.
• A certificate number and date for traceability.

These details matter for compliance. Councils and certifiers expect a certificate from an accredited assessor, produced in approved software. They also give the document an audit trail, so a certifier can confirm the certificate is genuine and current rather than an out-of-date or unofficial copy.

Specifications behind the rating

A certificate is usually accompanied by the schedule of construction details that produced the result. This is the part the builder must actually follow on site, and it is where the rating becomes real. Common items to look for include:

• Insulation values for the ceiling, walls and floor, written as R-values.
• Glazing performance, including the glass type and frame, often expressed as U-value and SHGC.
• Shading devices such as eaves, awnings and external blinds.
• Floor construction and any required coverings.
• Sealing and air-tightness measures.

If the build substitutes a cheaper product for any of these without re-checking, the home as constructed may no longer meet the rating on paper. The specification is a commitment, not a suggestion.

How to sanity-check your certificate

You do not need to be an assessor to catch obvious mismatches. Run through this quick list.

If anything looks off, raise it before construction. A small correction on paper is far cheaper than a change on site. If you want a second set of eyes, our team is happy to review a certificate and explain it in plain terms. You can learn more on our services page, and the outcome of any review depends on the specifics of your project.

Why the numbers can change

Ratings respond to design choices. Adjusting glazing, insulation, orientation, shading or air-tightness moves the loads and the star rating. That is the point of an assessment: it lets you test ideas before you build. If your first result falls short, there are usually several practical paths back to compliance, and an assessor can show you which ones suit your budget and design.

Some changes give more rating per dollar than others. Adding eaves or external shading to over-glazed western rooms, correcting the area of glass, choosing better-performing glazing units, lifting ceiling insulation and improving sealing all tend to move the result efficiently. Wholesale changes such as reorienting the building or rebuilding wall types are powerful but expensive, so they are usually a last resort. Because the levers interact, the most reliable way to find the cheapest route back to compliance is to test combinations in the software rather than guessing.

The whole-of-home picture

The star rating describes the thermal shell, but under the current rules a new NSW home is also assessed on its whole-of-home energy use, which takes in the major appliances. Your certificate should sit alongside the energy assessment covering heating and cooling, hot water, lighting and any onsite solar. Read together they give the true picture: a home can have an excellent shell yet fall short overall if it relies on inefficient appliances, while efficient appliances and solar can lift a borderline result. Check that the appliances listed match what you intend to install, because a swap to a less efficient unit on site can quietly undermine the result the documents promise.

Frequently asked questions

What is a good NatHERS star rating? New homes in NSW generally target 7 stars under the current rules. Higher is better for comfort and running costs, though the right target depends on your project and council requirements.

Why are the heating and cooling loads in MJ per square metre? Expressing energy per square metre lets homes of different sizes be compared fairly. It is the standard NatHERS measure behind the star rating.

What if the plan reference on my certificate is outdated? Treat it as a red flag and ask for it to be checked. The certificate must reflect the drawings you intend to build from, or it may not be accepted.

Building or renovating in NSW? Get a fast, fixed-fee quote from our HERA-registered assessors.