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Reading the stars of house energy ratings

When you build a new home or substantially renovate your existing home, you may receive an energy house star rating and report.  But what is it and what does it mean?  Why is the report important?  What else should you consider?

Here are some answer to frequently asked questions about house energy star ratings.

What is a house energy star rating?

The house energy star rating is a rating out of 10, with 10 being the optimum target to achieve.

The star ratings are determined in accordance with the Nationwide House Energy Rating Scheme (NatHERS) and focus on the heating and cooling load of the home as designed.  

In assessing the heating and cooling load, that is, the energy needed to maintain comfortable living temperatures year round, the star rating considers the following key elements:
Climate
Location
Orientation
Building materials
Shading
Thermal mass 

The rating does not consider the type of heating or cooling appliances or their efficiency.  It can not account for occupant behaviour.  

Other elements that are not considered are sustainability of materials, appliance efficiency, use of recycled materials, carbon, lifecycle assessment, etc.

Why does the house energy star rating only consider heating and cooling load?

The rationale for focusing on heating and cooling load only is that this accounts for 40% of the average energy use in Australian homes.  

Find out more about average energy use here.

How many stars should I aim for?

The more the stars, the more energy efficient your home for heating and cooling.  

The maximum star rating of a home is 10 stars, these homes require no external heating or cooling inputs.

The minimum star rating for new homes in South Australia is 6 stars; which aligns with the National Construction Code.

Does one star really make a difference?

Yes, it makes a big difference.  It is important to consider the longer term costs of living in a home, when you build a house.   
Results of moving from a 1 star home to a 6 star home are shown in the following graphic.

How are the stars determined?

There are a number of software tools that can be used by accredited consultants to determine the energy star rating of your new home.

The most popular software is FirsRate5, others include AccuRate and BERPro.

Plans for your new home are assessed, details with regard to climate, orientation, building materials, shading and thermal mass are entered into the software, and a report is generated to outline the house energy star rating.

Who can prepare a house energy star report?

Consultants must be accredited in the use of software tools for preparing a house energy star report.  You can find a list of accredited consultants here.

It is recommended that the consultant is independent of the architect, building designer or builder who has prepared the design and plans for your new home.

Example of a report for a home designed by Energy Aspect Living that achieved 7.9 star energy rating, as assessed by an independent accredited consultant.


Who uses the house energy star rating report?

During the design of your home, the designer may refer to a star rating report to assess the heating and cooling load performance.  At the design stage refinements may be made to make improvements and increase the star rating of your home.

The house energy star rating report forms part of the documentation that is used by your local government authority to assess your development application to ensure the rating achieves minimum requirements.

The house energy star rating report should be given to the builder of your home to ensure materials and construction methods align, and that the stars achieved at design stage are realised during construction.

If I make changes to plans or material during construction will this affect the star rating of my home?

Yes, it might.  It is important that if changes are made to your design after the house star rating report has been prepared, that a review be completed to assess if the star rating is affected.  Depending on what has changed, and the extent of change, it may be beneficial to prepare an amended house energy star rating report, this way you can understand the impact and make an informed decision.

How can I be sure the house energy star ratings are achieved when my house is built?

It is important that the builder has a copy of the house energy star rating report and reviews this in selecting materials and building the home.  

Window and glazing manufacturers should also be provided the report to ensure their systems align with glazing elements specified in the report.

When decisions on materials are made during the build, ensure that all decisions consider the house energy star rating report, as well as your budget.  Be careful not to underestimate the longer term cost of decisions made during the building process.

Is it possible to achieve 10 star house energy rating in South Australia?

Climate is a major influence to the ability to achieve 10 star house energy rating and due to South Australia’s variable climate it can be difficult (but not necessarily impossible) to achieve a 10 star house energy rating.

What else should I consider?

The house energy star rating considers heating and cooling load of your new home and its purpose is to minimise the energy required to keep your home comfortable year round.  Ultimately however the energy we use comes down to our lifestyle and our behaviour.

Other things you can also consider to make your home more energy efficient include:
Water heating – size, type and location of system
Lighting – type and number
Refrigeration – number of appliances, their size and efficiency
Appliances – number of appliances, their size and efficiency

Other things you can consider for sustainability of your new home include:
Water use
Waste minimisation
Indoor air quality
Recycled material use/content in materials sourced
Carbon and greenhouse emissions
Consumption

Why didn’t I get a house energy star rating report?

Sometimes an architect, building designer or builder may opt to use a different method of energy efficiency assessment call “Deemed to Satisfy”.  This method assesses the same elements of your home but does not require software and does not produce a house energy star rating report.  You may like to discuss the two methods with your architect, building designer or builder to better understand which method is best for your new home.