Building rating tools

Key points

  • Australia has various building rating systems.
  • The rating systems are used to assess energy efficiency and other aspects of sustainability for existing buildings or new building designs. Some rating systems assess building components.
  • Using a rating system can help you to ensure that the home you buy, renovate, or build is comfortable and energy efficient.
  • A Nationwide House Energy Rating Scheme rating is the most common way for new homes to meet the minimum energy efficiency requirements of the National Construction Code (NCC).
  • Some of the rating tools are free and relatively easy to use, while others require specialised software and are designed for use by professionals or an accredited energy assessor.
  • An accredited energy assessor can provide a rating to meet NCC requirements, and can also add value to your planning with professional advice on improving the energy efficiency of your home.

Building rating systems used in Australia

Rating tools can help you incorporate sustainability and energy-saving features into your home. Some tools allow you to model your home or to test how various changes will affect the rating. Some have been developed by governments, others by industry bodies or private companies.

Nationwide House Energy Rating Scheme (NatHERS)

Nationwide House Energy Rating Scheme assessments provide a star rating out of 10 that indicates the thermal performance of free-standing homes, townhouses, and apartments. The more stars, the better the potential thermal performance.

NatHERS ratings are the most common way for new homes, townhouses, and apartments to meet the minimum energy efficiency requirements of the NCC. They may also be used to identify how to maximise the thermal performance of a house design. CSIRO has developed a dashboard to show average NatHERS star ratings across the states and territories.

NatHERS rating tools

Four software tools are accredited to conduct NatHERS ratings: AccuRate, BERS Pro, FirstRate5, and HERO. The tools are based on a calculation engine developed by the CSIRO that can predict the temperature inside a building on an hour-by-hour basis for a whole year, based on its size, building materials, insulation levels, type and placement of windows, orientation, and climate zone.

The software makes standard assumptions about occupant behaviour to predict the heating and cooling load needed to maintain a comfortable temperature all year round. Included in the calculation engine are regional climate data and the thermal properties of all major materials. The NatHERS tools can model the complex effects of building mass, roof types, and many other factors, including levels of insulation, window size, and shading.

NatHERS thermal performance ratings do not include the energy use of appliances or the embodied energy of building materials. The actual amount of gas or electricity used for heating and cooling is influenced by the behaviour of the occupants, quality of construction and efficiency of appliances, in addition to the thermal performance of the building. AccuRate Sustainability and BERS Pro Plus have additional functionality to allow modelling of water use and other energy impacts such as lighting, hot water and major fixed appliances.

The Nationwide House Energy Rating Scheme, also known as NatHERS, rates a home out of ten stars based on the energy efficiency of its design.

Nationwide House Energy Rating Scheme logo

 

NatHERS tools can be used during the design process, or to diagnose thermal discomfort issues in an existing home if sufficient building information is available. This can be done at a building-envelope scale or room-by-room scale in both new homes and renovations. This feature allows a designer to identify rooms that may perform poorly under certain weather conditions, so that they can be modified to improve comfort. Designers may vary the building shape, window size and location, shading or construction materials to optimise the performance of the design.

A vertical bar graph of a demonstration house shows that the sitting room uses the most energy for heating and the kitchen uses the most energy for cooling.
Graph generated from NatHERS software output which shows the predicted energy consumption for each room in a house

Source: Adapted from Deslisle Hunt Wood

Accredited assessors

Anyone can buy and use the NatHERS tools. You can also employ a NatHERS accredited assessor to produce certified NatHERS ratings or provide energy efficiency-related building design advice.

National requirements for NatHERS assessments have been developed to facilitate consistency in entry and rating outputs, and NatHERS accredited assessors must abide by these requirements. A certified national training course for assessors (Certificate IV in NatHERS Assessment) has also been established, which adds to the robustness and quality of ratings from NatHERS accredited assessors.

Find contact details for accredited assessors in your area from the Australian Building Sustainability Association, Design Matters National, and
House Energy Raters Association.

Changes to NatHERS

NatHERS is being expanded to offer nationally accredited whole-of-home tools. NatHERS Whole of Home will provide information about the energy performance of fixed appliances (for example, hot water system, heating and cooling appliances, energy generation, lighting, pool and spa pumps) and the overall energy performance of the home (that is, the thermal performance of the home combined with the performance of fixed appliances).

Expanding NatHERS to assess and rate the energy performance of the whole home will:

  • support designers, builders and homeowners to exceed minimum standards and achieve a zero energy (and carbon) ready home
  • support a range of initiatives, such as enabling banks to use NatHERS ratings to underpin green home loans
  • cater for potential future energy efficiency requirements in the NCC.

Whole of Home logo

NatHERS Whole of Home will rate the energy performance of these aspects of a home.

 

National Australian Built Environment Rating System

The National Australian Built Environment Rating System (NABERS) Home Rating Calculator is an easy-to-use tool for comparing the energy and water use of an existing home to that of an average household. This web-based tool is available for anyone to use. The website also provides diagnostic tools – Energy Explorer – for further advice.

Because it focuses on the interaction between the occupants and the building rather than the technical potential for that building, the NABERS Home Rating Calculator provides a realistic assessment of how a home, as used by its occupants, is actually performing.

The NABERS Home Rating Calculator is not a predictive tool. It can be used only for an existing home that has been occupied for 12 months and allows a check on whether the home is performing as well as it has been designed to. A NABERS home rating analyses 12 months of actual energy or water use billing information, and supplies a rating out of 6 stars, with 3 stars representing an average household. This can provide beneficial information when thinking about a renovation or building upgrade.

The NABERS Calculator complements, rather than replaces, other rating systems that focus on the design stage, such as NatHERS. It cannot be used to meet the regulatory energy efficiency requirements in the NCC.

NABERS for Apartment Buildings rates the common areas of apartment buildings (lifts and lobbies, pools, gyms and car parks) but not the apartments themselves. NABERS for Apartment Buildings gives a star rating out of 6, and is designed to encourage building owners or owners corporations to make building improvements to increase their rating.

Building Sustainability Index

The New South Wales Government’s Building Sustainability Index (BASIX) establishes minimum standards for all new freestanding houses, multi-dwellings and alterations and additions to existing dwellings in the state.

BASIX is applied through a New South Wales planning regulation that sets percentage reduction targets for greenhouse gas emissions and water use for dwellings of a similar type in the same geographical location. BASIX also sets a minimum level for building envelope thermal performance and covers a wide range of household energy uses by fixed equipment such as heating and cooling appliances, lighting, and hot water.

BASIX is a web-based tool that is available for use by anyone, although users must register and log in. The data that needs to be entered into the program include the location, size, building materials, appliance and equipment selection, and design of the building. BASIX analyses these data and determines how the data score against prescribed energy and water targets. The home design must pass specific targets – which vary according to location and building type – before a BASIX certificate can be generated. The BASIX certificate is lodged with your development application to your local council for approval, and is later lodged with your construction certificate and occupation certificate.

In New South Wales, the online BASIX system replaces the NCC energy efficiency requirements. BASIX accepts NatHERS software results as one way of meeting its separate targets for the heating and cooling performance of the building.

Victorian Residential Efficiency Scorecard

The Victorian Government developed the Victorian Residential Efficiency Scorecard which is a voluntary home-efficiency rating tool for existing homes. It is currently only available in Victoria.

To get a Scorecard rating, an assessment is carried out on-site by an accredited assessor. The assessor evaluates the physical attributes and systems in the home, including heating and cooling devices, pool and pumps, hot water systems, solar photovoltaic systems and the construction of the house.

The focus of the Scorecard is the cost of energy consumption, although it also has a ‘hot weather rating’ and a ‘cold weather rating’ to assess how comfortable the house is in extreme weather - without artificial cooling being used.

The Scorecard is paid for by the homeowner and usually takes around 2 hours. The Scorecard star ratings reflects the cost of running the fixed appliances in the home on a 1 to 10 star scale. The scale is designed so that the average home rates at 3 out of 10 stars. Using this as a baseline indicator, a 6-star home will be more comfortable and have the potential for lower energy bills than most homes. An 8-star home is highly efficient and delivers real benefits in comfort and cost to householders. A 10-star home is as good as it gets – this is achieved when the energy used by fixed appliances is more than covered by the energy produced at the home by solar PV.

Green Star

Green Star was launched by the Green Building Council of Australia (GBCA) in 2003 and is a voluntary environmental rating system for buildings and communities. Green Star evaluates the environmental design and construction of new and refurbished buildings and the sustainable planning, design and construction of new communities. The Green Star Design and As Built rating tool is able to rate all types of buildings, except detached residential dwellings. A Green Star standard to rate new and existing detached homes (focusing on off-the-plan homes by volume builders) is due to be released in 2021.

The Green Star tool evaluates environmental issues – such as minimising energy and water consumption, reducing greenhouse gas emissions, managing waste and reducing dependence on motor vehicles – as well as broader holistic sustainability issues such as economic prosperity and affordability, liveability, design, governance, and innovation.

Green Star certifies ratings as 4 star (best practice), 5 star (Australian excellence) and 6 star (world leader). Projects under 4 stars do not qualify for a certified Green Star rating.

Green Star provides best-practice benchmarks that building owners and managers can use to set targets to increase energy and water efficiency, reduce waste, and improve factors that influence productivity, health, and learning, such as indoor environment quality.

Passive House

Passive House or Passivhaus as it is known in German, is a design standard that requires appropriately insulated, airtight buildings with mechanical heat recovery ventilation .The definition of a Passive House is ‘a building, for which thermal comfort (ISO 7730) can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air’.

The Passive House Institute (PHI) administers an international certification scheme, carried out by a PHI-approved Passive House Certifier.

Living Building Challenge

The Living Building Challenge was first launched in 2006 by the International Living Future Institute. It requires buildings to mitigate all of their environmental impacts and give more than they take from the world.

The criteria are place, energy, water, health and happiness, materials, equity, and beauty. Unlike many tools, certification is achieved only when all of the criteria have been met, rather than a points-based system. Several of the criteria (energy, water) require the building to be operational for at least a year to prove that it does achieve their performance targets.

There are currently no certified Living Buildings in Australia, although there are several that are working towards certification, including a retail shopping centre in Melbourne.

WELL Building standard

The WELL Building standard was developed by the International WELL Building Institute in the United States. It focuses on the health and wellbeing aspects of buildings and is mainly used as a rating tool on commercial buildings. The design criteria are broad, from indoor air quality and thermal comfort to credit for encouraging healthy eating in the workplace.

Window Energy Rating Scheme

The Window Energy Rating Scheme (WERS; rates windows, window films, skylights and glazed doors for their energy performance, based on the solar, thermal and optical properties of the glazing unit and frame. These properties are determined by a combination of laboratory measurements and computer simulations.

Products rated in WERS earn from 0 to 10 stars for cooling (summer) and heating (winter), depending on how they rank against the alternatives. WERS also provides performance values which include U value, solar heat gain co-efficient (SHGC), light transmittance, and air infiltration rate (see Glazing in the Passive design section). The ratings apply to the effect of the whole assembly including the relative contributions of glass and frame. The rating information can be used in energy rating tools, such as NatHERS, to estimate the actual impact on performance for any house. The WERS Certified Product Hub allows for filtered searching to find the window performance that best suits your needs.

WERS is managed by the Australian Glass and Window Association (AGWA), which is made up of window manufacturers and industry suppliers throughout Australia. It is an accredited member of the Australian Fenestration Rating Council.

 

Window Energy Rating Scheme logo

Window Energy Rating Scheme logo

 

Interpreting ratings

There are some things to consider in interpreting building or product ratings.

  • Is the rating of a building element, such as a window, a true representation of its performance in the real world?
    No. The performance of a building element needs to be considered in context. For example, in a warm climate, a WERS 5-star rated window with no shading will cause more overheating in summer than a similar sized 0-star rated window with well-designed shading. This is because effective shading blocks out more radiant heat.

  • Is the rating of a whole building a true representation of its performance in the real world? Not necessarily. Some tools (known as predictive tools) predict the energy use of a building, and some tools rate the actual energy use. Predictive tools can be used for regulatory purposes before a building is built, but they may not be as good at predicting actual energy use after the building is built, because they do not account for the differences in how people use and occupy their home. 

  • Does the rating system address relative size in assessing the overall impact?
    No. A 400m2 home and a 150m2 home may have the same star rating. However, the larger home will use more resources and embodied energy in its construction than the smaller home. Note that tools such as NatHERS, NABERS, and BASIX do not consider embodied energy. The larger home will also require more heating and cooling energy to be comfortable.
  • Do building ratings take into consideration all the environmental impacts?
    No rating tool can incorporate every environmental impact and some incorporate a broader range of impacts than others, but better ratings will generally lead to better environmental outcomes. Try to also consider those environmental aspects that may not be easy to measure, such as embodied energy. For example:
    –    Many ‘low embodied energy’ solutions may have higher embodied energy than realised (for example, blending cement into mud brick or rammed earth walls dramatically increases their embodied energy). Some low-embodied-energy systems require high-embodied-energy foundations or structural components. 
    –    Features other than the building, such as paved driveways, may add substantial embodied energy.
    –    It is possible to select lower embodied-energy products within each material type (for example, bricks made in energy-efficient kilns or recycled bricks, or concrete that includes blast furnace slag or other ‘extenders’). Refer to Embodied energy in the Materials section.

References and additional reading

Learn more

Authors

Original authors: Chris Reidy, Chris Reardon, Geoff Milne 2013

Updated: Andy Marlow 2020