How to make your home energy efficient

If you've spent a winter in the average house, you'll know just how much you need to crank the heat to stop shivering. Purchasing an inefficient house could cost you hundreds of dollars more on energy each year, but this crucial information isn't made available when buying (unless you live in the ACT).

• In fact, it's estimated that a 3-year delay in raising Australian building standards will cost residents an extra $1.1 billion in energy bills by 2050, and produce 3 million tonnes of greenhouse gas.

In this guide, we'll walk you through determining your own house's energy star rating and what it means, as well as what you can do to improve it.

How is the energy efficiency of a home measured?

In Australia, houses get a star rating out of 10 for efficiency, defined by the Nationwide House Energy Rating Scheme (NatHERS). Here are a few examples on the scale:

A 0-star home may as well be open to the elements.

A 6-star home does a decent job of blocking out hot or cold weather, but probably needs a fan in summer or heater in winter.

A 10-star home will likely keep you comfy all year round by itself.

To give you an idea of how this might impact your bills, a 5-star house uses between 20–25% more energy in heating than a 6-star one.

How energy efficient should my house be?

Ideally, you want the highest star rating possible, since it will save you the most on heating and cooling costs.

New houses in Australia

New houses in Australia are required to meet a 6-star rating minimum, although this doesn't always happen.

According to Sorn Vimonsatit, Associate Professor at the School of Engineering in Macquarie University, the incentive isn't there for houses.

"For office buildings, the developer relies on rental income," she says. "They will put much more focus into how to make it appealing. If the developer builds to sell, the incentive to see long-term energy costs isn't there."

What's optimal?

A CSIRO study from 2019 identified 7.5 stars as an optimal star rating, balancing out extra upfront construction costs with lifetime savings on energy.

What is the average?

Currently, the average Victorian home is rated a measly 3 stars, far from even Australia's minimum standard. Globally, we're even worse, with Australia's building standards already 2 stars behind similar developed countries back in 2008.

What should I consider when purchasing a house?

It's important to get as detailed information as possible about the house's design, and not settle for the basic assurances offered by real estate agents.

"People are told 'this is well-insulated', and they're happy," says Professor Vimonsatit. "But it's not enough."

"In an old house, you'll see… double brick cavity walls. But between the wall and the roof... you'll see a big gap here and there, so it doesn't serve the purpose of having proper insulation."

So how do I make my home more efficient?

Once you've had your house audited or done it yourself, you can split up improvements into a couple of categories.

Do it yourself

• Shades

  Proper shading can block up to 90% of incoming heat. This includes blinds, curtains or retractable awnings on windows, but also leafy trees to shade windows and walls that frequently face the sun.

• Plugging leaks

  Can save about 10–20% on energy costs per year. Air can leak in through holes in mortar or house sidings, but also holes drilled for fixtures like taps, electrical outlets and more.

• Appliances

  Appliances make up around 20% of your energy bill. You can choose more energy efficient lights (10% of your bill), for example. We have a guide on some simple household saves, plus the 5 most energy hungry appliances in your house.

Call a builder

• Insulation

  Insulation is critical to efficiency, with good insulation cutting down heat loss/gain by 50% or more. Insulation is measured with an "R-value": how well it resists heat transfer. The government's "Your Home" guide recommends a minimum R-value of 4.1 for your ceiling/roof, and 2.8 for your walls.

• Glazing

  Windows are notorious for transferring heat. Getting your windows glazed or double-glazed slows down heat transfer in winter by up to 20%, or up to 35% in summer.

• Solar

  While solar panels don't technically impact your home's star rating, they can save you money in the long term and reduce your carbon footprint. We have a guide on estimated returns for solar panels here.

• Roof colour

  In most cases, this is far too expensive to be practical, but switching out your dark roof tiles for a lighter colour could make an almost half-star difference in your energy rating. This is especially true in warmer climates.

Unfortunately, according to Professor Vimonsatit, most efficiency measures are implemented during the design process.

"If you buy a house that's already built," she says, "the only thing you can do is get insulation, or some sort of solar energy. There's not much you can do in terms of ventilation [which] is about the direction of windows and doors."

More drastic efficiency improvements

If you're really invested in fixing up your current house and not simply moving, there are more dramatic improvements available. These will likely require extensive renovations and thousands of dollars to implement in existing houses, and are easier when designing a house.

Example: 4 eco design ideas from a 9-star Penola House

Here are some clever ideas and eco-measures implemented in Penola House, a 9-star dwelling in Melbourne. The house cost $420,000 to build, and uses 80% less energy for heating and cooling than a 6-star house (or one-tenth the energy of average existing houses).

* This is a fictional, but realistic, example.

Is it worth improving my house to make it more energy efficient?

Boosting your house's star rating can take a lot of work and money, but there are a number of long-term benefits.

And remember, full renovations may cost a lot, but cheaper measures like improving seals around doors and windows could cost as little as $15 per square metre.

1. Reducing heating bills

Increasing your star rating has huge impacts on energy costs in the long term. A jump from 5 stars to 6 stars should cut your heating costs by around 25%, and aiming higher could be a smart financial decision.

A 2018 study by the University of Melbourne found that a full energy retrofit of houses in Melbourne's Bayside area to a 6-star standard would take 14 years to pay itself back. A 5-star renovation would need 15 years, meaning cheaper isn't necessarily better.

2. Improving the property value

Even if you're not planning to stay in your house forever, more stars means a higher resale price. In Australia, the University of Wollongong found that a higher star rating is typically associated with around a 5–10% premium on the sale price.

When compared to a 3-star home in the ACT, for example, a 6-star house attracted a 2.4% premium and a 7-star house a 9.4% premium.

3. Lowering the carbon footprint

Buildings produce around 25% of Australia's carbon emissions, and houses are a big part of that. Improving your house's energy rating will reduce your personal carbon footprint far into the future.

Finder survey: Have many Australians have upgraded an appliance so that it's more energy efficient?

Where are the most energy-efficient houses in Australia being built?

Short answer, the ACT and Tasmania.

While the 6-star minimum applies around Australia, some states are doing better than others when it comes to building new houses. Here are the average NatHERS star ratings for new houses built in various states between 2016 and 2018.

Source: The Conversation. NSW and NT have been excluded due to different building standards schemes.

As you can see, colder climates come with slightly better-built houses. If you're looking for an efficient new home, you'll have the best luck in the ACT or Tasmania.

Interestingly, the ACT showed the most improvement from 2016, which could be due to transparency in its property market. It's the only Australian region where real estate agents have to reveal the property's energy rating on sale or lease, letting buyers potentially demand a higher standard.

Buyers in other states simply don't have the information.

Who determines my home's energy efficiency?

Minimum house efficiency standards are dictated by the National Construction Code (NCC), which is published by the Australian Building Codes Board. Each state and territory has its own regulatory bodies to enforce the NCC.

Nationwide House Energy Rating Scheme (NatHERS)

NatHERS is the system that rates houses out of 10, based on the efficiency of their design. A NatHERS assessment evaluates a new home prior to construction, and makes sure they adhere to a minimum of 6 stars.

National Australian Built Environment Rating System (NABERS)

NABERS is a tool used to compare water and energy consumption of an existing house against other average households, unlike other schemes that apply during the design phase only.

It uses 12 months of water and energy bills to come up with an efficiency rating between 1 and 6 stars, with 3 stars corresponding to average performance.

Green Star

The Green Star rating is awarded to buildings after construction is completed, and is managed by the Green Building Council of Australia.

The building's sustainability is assessed and awarded a star rating out of 6, assuming it meets minimum sustainability standards. A 1-star rating indicates bare minimum practice, while 6 stars indicates world leadership in sustainable design.

NSW Building Sustainability Index (BASIX)

BASIX is an online tool that applies to all new developments in New South Wales, as well as renovations and extensions that cost $50,000 or more. It sets minimum water and energy consumption targets when houses are being designed, taking into account heating and cooling appliances, hot water and more.

Victorian Residential Efficiency Scorecard

A program implemented by the Victorian government that provides star ratings for your home. Government-approved energy assessors will inspect your house and give you a report for a certain price.

The report judges your house on building quality, hot water and more, and recommends cost-effective improvements to raise your house's rating and lower energy costs.

Houses don't always end up as efficient as required

The National Construction Code allows several methods of verifying the efficiency of a new home, outside of the NatHERS star rating system. These are:

• Elemental provisions. This evaluates insulation, building sealing and window construction.
• Performance solutions. An alternate method for assessing unique houses that involve new technologies or non-standard construction.
• Verification using a reference building (VURB). Similar to elemental provisions but with slightly different requirements.

The VURB method awards a simple pass or fail instead of a star rating, which can lead to substandard houses.

"The requirements from the building code are more in terms of… energy consumption," says Professor Vimonsatit. "They talk about ventilation and all that, but it's still not very measurable."

Buildings verified by VURB may lack efficiency features like slab insulation or glazing on windows, and have an equivalent star rating below the NCC's minimum.

Learn more about energy

Our energy guides can help you compare and understand what plan is best for you.

Best energy plans: 5 plans selected by our experts, assessed and updated regularly

Cheap energy plans: Find the cheapest energy plans available this month

Solar power plans: Got rooftop solar? Compare your options and save even more

Average energy bill: Find out how your energy bill compares to the rest of Australia

Written by

Sam Baran

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Sam Baran is a writer for Finder, covering topics across the tech, telco and utilities sectors. They enjoy decrypting technical jargon and helping people compare complex products easily. When they aren't writing, you'll find Sam's head buried in a book or working on their latest short story. Sam has a Bachelor of Advanced Science from the University of Sydney. See full bio