Understanding your Home’s Energy Rating

If you’re building a home, you’ve probably heard the term ‘energy rating’ thrown around here and there. If you don’t know much about energy ratings and their significance, it’s worth spending some time to try and understand Australian home energy efficiency requirements, as they can significantly impact the design and structure of your home.

What is an energy rating?

The National Construction Code (NCC) includes energy efficiency requirements for new homes and major renovations. These standards aim to improve the energy performance of buildings, including aspects like insulation, window performance, and heating and cooling systems.

Australia’s Nationwide House Energy Rating Scheme (‘NatHERS’) assesses residential dwellings and provides ratings based on their energy efficiency. While there are other pathways to compliance, new homes commonly use NatHERS ratings to meet the minimum requirements set out in the NCC.

Energy assessors use NatHERS computer modelling tools to estimate a home’s energy efficiency. The NatHERS software is based on a calculation engine developed by the Commonwealth Scientific and Industrial Research Organisation. This calculation engine can predict the temperature inside a building on an hour-by-hour basis for a year. It also helps to provide a valuable overview of energy costs and greenhouse gas emissions.

A NatHERS assessment provides a ‘thermal performance’ star rating and a ‘whole of home performance’ rating.

Thermal Performance Ratings

A Thermal Performance Rating is an assessment of how much heating or cooling is expected to be required each year to keep a home within a comfortable temperature range. The following criteria are considered when measuring a home’s thermal performance (particularly with respect to the roof, windows, walls and floor):

• Design
• Materials
• Construction
• Insulation
• Size, layout & orientation
• Shading & how your home is designed to capitalise on local breezes

Based on the results, your home will be given a rating between 0 and 10 stars. The higher the star rating, the more energy efficient your home is. The NCC was recently amended to introduce a minimum 7-star efficiency rating for new homes.

NatHERS provides the following general guide to star ratings:

• a 0-star rated home is quite uncomfortable – too hot in summer and too cold in winter. It will require a lot of energy to heat and cool.
• a home reaching a 7-star rating will need some mechanical heating and cooling to keep it comfortable to live in.
• a 10-star home is very energy efficient. It will remain comfortable year-round, with limited, or no mechanical cooling or heating.

Whole of Home Performance Ratings

Whole of Home Performance Ratings indicate the efficiency of appliances used in a new home, including heating and cooling, hot water systems, lighting, pool/spa equipment, cooking and plug-in appliances, and on-site energy generation and storage.

Based on the results, your home will be given a rating out of 100, where 100 is a net zero energy value home. The higher your score, the more energy efficient your home is. In other words, a high score means your home uses less energy than it generates.

How do I arrange an energy assessment?

While anyone can purchase the NatHERS software, we recommend finding an NatHERS accredited assessor to generate a certified NatHERS rating. If you consult with an assessor during the design stage of your build, they will be able to provide you with advice on how to increase your energy rating by choosing appropriate materials, amending the layout of your home, and more. You can find accredited assessors through the following links:

• ABSA’s Accredited Assessor Directory
• Design Matters Energy Efficient Assessors Database

You can also complete the referral form on the House Energy Rater website for a tailored shortlist of assessors who are qualified to advise on your project.

What can you do to help?

While having an energy efficient home will help to minimise the environmental impact and reduce costs for yourself and future buyers, how much energy you save will depend on your personal habits. Having an energy efficient home is only step 1; it’s important to take regular action to reduce your energy consumption. For example, open windows to let in air and light instead of turning on lights and air conditioning. Over time, this will make an impact on both your utility bills and the environment. If you’d like to learn more about energy efficiency ratings and NatHERS, you can do so here. We also recommend checking out NatHERS free home designs – a set of three energy efficient homes that can be customised to suit your needs.