Common questions about home energy efficiency
I’m in Melbourne and I’ve never lived in a house that stays warm in the winter or cool in summer without spending a fortune on energy. Is it even possible?
Yes it is! More and more homes are being built that need very little help from heaters and air-conditioners to keep comfortable all year round. These homes are designed using passive design principles, where micro-climate, solar orientation, insulation, thermal mass, shading and ventilation are all carefully considered in response to the local climate. There’s also a suite of options available for significantly improving the thermal performance of an existing house. Read on!
What is a NatHERS Star rating?
Energy use for different star ratings
All new homes in Victoria and major alterations/additions to existing homes must meet minimum energy efficiency requirements in order to meet code and gain building approval. NatHERS (Nationwide House Energy Rating Scheme) is a star rating scheme that uses sophisticated software to model the thermal performance of a proposed home in a given climate zone. As of May 1st 2024, if the design achieves a star rating of 7 Stars out of 10, the home satisfies the minimum thermal performance requirements of the building code. The average existing home in Victoria has been estimated to be just 1.8 Stars - that means if you were to bring an average home to the minimum 7 Star rating, you would theoretically reduce the energy required to heat and cool the home by about 80%!
The change to 7 Stars in Victoria is an improvement of about 27% on the previous minimum of 6 Stars.
If you were to go further and achieve 8 Stars, in Melbourne’s climate zone you would theoretically need less than half the energy of a 6 star home. That’s right, 8 Stars is twice as good as 6 Stars.
One of the strengths of NatHERS is climate-responsiveness. The software developed for the scheme defines 69 different climate zones in Australia, which are based on 25 years’ worth of hourly weather data gathered by the Bureau of Meteorology.
The Star rating scheme is useful not only for prescribing a minimum standard of thermal performance, but for comparison between homes; a home’s Star rating is already becoming one of the standard measures of house value along with size, location and number of rooms.
Why thermal performance?
The thermal performance of your home will determine how comfortable and healthy it is to live in, and how much energy will be needed for heating and/or cooling. Heating and cooling usually contributes to the greatest amount of energy use in a home. Furthermore, lots of heating and cooling equipment takes up space, is unsightly, can be noisy and in the case of reverse-cycle air-conditioners, will make the outdoors even hotter on a hot day.
This is why many people and organisations advocate an ‘envelope first’ approach to home energy efficiency. The envelope refers to the floors, walls, ceiling/roof, windows and doors - the permanent parts of a building that separate the outside from the inside. Getting these things right, along with the layout and orientation of the house, is a critical first step in energy efficiency. Additionally, a better thermal envelope means a quieter, healthier home. Once the fundamentals are designed for energy efficiency, it’s time to look at the efficiency of the (now smaller) heating/cooling equipment, the hot water heater, appliances, lighting, and plumbing fixtures. Finally, once the energy demand for the house has been reduced to a minimum, it’s time to look at clean sources of power to meet that small energy demand.
All of the steps are important, but thermal performance is the first step to consider.
What about efficient appliances and solar panels?
As of May 1st 2024, a NatHERS rating for a new home in Victoria will also need to include a “Whole of Home” (WoH) rating in addition to the “Thermal” (Star) rating. The rating is based on the efficiency of heating and cooling appliances, hot water systems, lighting, cooking and pool pumps as well as any solar panels and home batteries. In addition to rating at least 7 Stars for thermal performance, a new home must rate at least 60 out of 100 for the WoH rating. It is worth noting that the higher the thermal Star rating, the higher the home will rate on the WoH scale. In theory, a WoH rating of 100 or more means the home will produce as much energy as it consumes.
What about embodied energy?
A restored cedar door and recycled floorboard shelving reduce the embodied energy on this project. Image credit: Monica Styles
Although thermal performance is the first step to consider for a home to operate efficiently, embodied energy is actually the first expenditure of energy a home makes. For a building, embodied energy is the energy consumed in all the processes required to make the building, and does not include the energy used to operate the building. (Related concepts are embodied carbon and embodied emissions). Measuring embodied energy is notoriously tricky; even trickier is measuring all the other environmental and social impacts associated with procuring materials and the construction process. However, there’s no need to be put off as there are some good rules of thumb that will always help to reduce energy demand along with other negative impacts from the building industry:
Reduce: Build less. Does your house need to be replaced, or could it be retained and improved? Tochi is always looking for ways to tip the balance toward working with existing structures - not only is it better for the planet, it is satisfying to build on the layers of history and character in a home. How big does your place need to be? It’s amazing what good design can do to transform a space that seemed inadequately sized to begin with.
Re-use: If you’re demolishing, are there things that you or someone nearby can re-use? If someone else is demolishing nearby, do they have something you could re-use yourself?
Recycle: If you’re demolishing, make sure the materials that can’t be re-used straight away are sent to be recycled. And of course, use recycled products or products with high recycled content where possible.
Aim for durability: The longer buildings endure, the less embodied energy impact they have over time. Durability means more than structural soundness, a building needs to be designed for long-term desirability both functionally and aesthetically.
Where can I learn more about energy efficient housing?
There are numerous resources floating around, here are just a few favourites:
Renew is a non-profit organisation that does loads of work to transform Australian homes for climate resilience. Check out all their exciting publications and events via their website.
Light House Architecture & Science journal:
There’s loads of practical, accessible information about building science and energy-efficient architecture on this website. Best of all, there’s plenty of photos and articles about beautiful real-world examples of energy efficient homes they’ve designed. Light House director Jenny Edwards is trained as a scientist and science communicator and has done a lot of pioneering work with her team on high performance homes in Canberra’s challenging climate.
Your home is a handy free guide to sustainable home design from the Australian Government. Very accessible and a good starting point if you’re planning to build or renovate.
An award-winning think tank that publishes excellent and impactful research on topics relevant to Australia’s pathway to zero emissions (and beyond). There’s also many other events, initiatives, and volunteering opportunities happening all the time.
My Efficient Electric Home (MEEH)
MEEH is a super-active Facebook discussion group, run by some very knowledgeable and enthusiastic moderators. The lively discussions range across a wide number of topics, but it’s all about disconnecting from gas and other fossil fuels and raising energy efficiency in the home.