Issue 7 - December 2018


Welcome to the seventh edition of the NatHERS Star! This edition focuses on the progress of ongoing improvements and updates we are currently working on for NatHERS.

This year's achievements

It has been another busy year for the NatHERS Administrator. This year’s achievements include:

  • Responded to approx. 200 email and phone enquiries
  • Worked with software tool providers to progress numerous bug fixes and minor updates to the NatHERS tools
  • Received approval on the NatHERS updates that will align with the 2019 version of the National Construction Code (NCC)
  • Updated the NatHERS interactive map
  • Released biannual newsletters and special edition news updates throughout the year
  • Participated in Sustainable House Day and raised awareness about NatHERS
  • Received stakeholder feedback and direction through regular meetings and workshops
  • Progressed a number of significant projects that are almost complete, including the update of the NatHERS Technical Notes, revamp of the NatHERS Certificate, development of an Assessor Handbook and establishment of a new Software Accreditation Protocol.

NatHERS Stats

The NatHERS certificate data captured by the CSIRO in conjunction with Sustainability Victoria from September 2017 – September 2018 shows:

Building Class             Number of Certificates
Class 1 146,911
CLass 2 69,945
Class 4 83
Total: 216,939

And did you know?

  • An average Class 1 dwelling for this period was 6 stars, 146.5m2 and predicted to use 27.43 MJ/m2 cooling and 86.31 MJ/m2 heating.

  • An average Class 2 dwelling for this period was 6.3 stars, 74.8m2 and predicted to use 22.92 MJ/m2 cooling and 40.27 MJ/m2 heating.

  • At the end of the 2017-18 financial year there were over 600 NatHERS Accredited Assessors nationally.

Fraudulant NatHERS Certificates

Recently the NatHERS Administrator has received, and been following up on, a number of NatHERS Certificates that have been suspected to be fraudulent. We are committed to ensuring the credibility of the Scheme is maintained and will be continuing to follow-up and address all potential fraudulent behaviour brought to our attention.

If you think a NatHERS Certificate may be fraudulent, please provide the Certificate and details to The NatHERS Administrator has produced two fact sheets that explain what to look for on a NatHERS Certificate. These will be circulated to building certifiers, industry peak bodies, state and territory governments, as well as being made available on the Fact Sheet page of the NatHERS website.

NatHERS Assessor Handbook

The NatHERS Handbook is being developed by the NatHERS Administrator in conjunction with industry experts, with progress now well underway. Designed to help assessors navigate the NatHERS assessment process, the Handbook describes how assessments should be conducted and explains the mandatory and recommended steps of the process.

7 of the 10 chapters of the Handbook have now completed a consultation period, and the NatHERS Administrator is currently collating the feedback received, whilst working with the graphic designer to produce the final version for release. It is anticipated the NatHERS Handbook will be released in early in 2019 to align with the release of an updated NatHERS Technical Note and Chenath changes. This release will also align with the NCC update scheduled for implementation from May 2019.

Once published, the NatHERS Handbook will be available on the NatHERS website and communicated to state and territory building authorities, and to assessors through Assessor Accrediting Organisations (AAOs).

NatHERS at Sustainable House Day

Sustainable House Day was held on Sunday 16th September 2018. For more than 18 years this annual event, organised by Renew (previously known as the Alternative Technology Association), has given hundreds of thousands of people the opportunity to visit some of Australia’s leading sustainable homes. The 2018 event saw 33,000 people visit 226 homes across Australia. View the full 2018 Sustainable House Day report online.

Sustainable House Day 2018 was also an opportunity to promote NatHERS and help educate the public on how the Scheme works. Renew published an article on behalf of the NatHERS Administrator communicating what is NatHERS and how it works. See the article here and please share it with your networks.

Modelling obscure glass

It has been brought to the attention of the NatHERS Administrator that there is industry confusion as to how to correctly model obscured glass in NatHERS accredited software tools.

Obscured glass (frosted, fritted, film) is classified as a complex glazing system, which is not yet approved internationally through the National Fenestration Rating Council (NFRC). Therefore, the Australian Fenestration Rating Council (AFRC) are not currently capable of obtaining WERS ratings for these types of products. The custom windows library is managed and provided to NatHERS software tools by the AFRC and is based on WERS ratings.

Given obscured glass products are not in the current Custom Windows library (because they have no WERS rating), the NatHERS Administrator is currently reviewing and updating the NatHERS Technical Note to provide a clear direction for what assessors should do when obscure glass is specified. If using default windows, the best fit window currently available is to select the appropriate default ‘clear’ window option.

It is anticipated that complex glazing systems may be approved internationally through the NFRC and subsequently the AFRC in mid-2019, allowing products like this to be better incorporated into the NatHERS software tools and energy assessment.

Additionally, there is a NatHERS fact sheet available on our website explaining how windows impact on a home’s energy performance and the different types of windows that can be used in NatHERS assessments.

Update on Windows

The NatHERS Administrator continues to actively work on improvements to address concerns regarding windows.

Assessors may be aware the Custom Windows Library update scheduled for November was postponed, as it was highlighted an appropriate versioning control solution should first be initiated. Resolving these issues is complicated, and more issues have come to light during this process. The NatHERS Administrator has prioritised addressing these issues and is currently working with Australian Windows Association (AWA), AFRC and NatHERS software tool providers to ensure the best outcome is achieved.

Chenath updates for 2019

The Australian Building Codes Board (ABCB) have approved the following updates for the Chenath engine in line with the 2019 update to the NCC. These Chenath updates will improve accuracy of ratings and solve some long-standing issues with the software. The items to be updated include:

- Improve double height voids modelling

The new double height voids modelling methodology will incorporate the upper void area into the downstairs zone to become one zone. Along with improved calculation of air flow between vertical and horizontal openings between adjoining zones, this approach allows heat from windows in the upper portion of the zone to be correctly allocated to the floor of the zone.

- Improve basement zones in apartment buildings modelling

The new basement zone applies to basements below apartments (typically carparks) where the floor of the basement is in contact with the ground and the external walls are either fully or partially adjacent to earth. This will improve the precision of assessments by applying a more accurate air infiltration/ventilation rate for relatively enclosed basement car park zones in apartment buildings.

- Improve modelling of apartment corridor zone

The new corridor zone has been developed to replace interim procedures and give assessors the option to model the corridor as external to the dwelling. The new zone is un-air-conditioned and includes glazed windows and/or glazed doors on one or more external walls. This will improve the precision of assessments by applying more accurate characteristics (primarily heat transfer) to the zone ‘neighbouring’ the apartment being assessed.

- Improve edge slab insulation modelling

The improved edge slab insulation modelling results in no changes to the scratch file for Chenath calculations. Neither software tools nor assessors are required to incorporate or learn a new modelling approach, but these changes will provide better slab-on-ground heat transfer calculations as part of an assessment.

- Improve waffle pod modelling

Recent CSIRO modelling showed that waffle pod values should be adjusted to represent their true performance. The improved waffle pod modellilng does not require software tools nor assessors to incorporate or learn a new modelling approach, but the overall accuracy of an assessment will be improved.

- Addition of limestone material

Limestone and its relative thermal properties has been included in the materials database of the Chenath engine library.

These updates will be accompanied by an updated Technical Note and an updated NatHERS Universal Certificate (which is also addressing items raised in the recent review that is available here). An updated Software Accreditation Protocol is also being finalised to ensure these updates are rolled out uniformly in all tools.

Split heating and cooling loads

The ABCB recently announced maximum heating and cooling load limits for the NatHERS pathways in the NCC, to support improving the performance of new homes in Australia. The NatHERS Administrator is currently working through the implementation of this amendment and advice on changes to assessments will be provided to assessors before modifications become live. There will also be a transition period for these requirements from 1 May 2019 until 1 May 2020 where the current requirements (NCC 2016) will still be accepted. For more information about the work already undertaken on split heating and cooling load limits, have a look at the ABCB report.

Trajectory for low energy homes

Australian governments are advancing the energy performance of residential and commercial buildings through the development of a Trajectory for Low Energy Buildings (the Trajectory). The Trajectory identifies cost effective opportunities for energy efficiency improvements throughout the building system, from thermal performance to appliance energy usage and potentially renewable energy generation.

Cost effective improvements to Australia’s building stock could significantly improve Australia’s energy productivity and reduce running costs for consumers. Preliminary analysis indicates that changes to the NCC in 2022 could deliver household bill savings of over $650 each year in colder or tropical climates, such as Canberra, Townsville and Darwin, and around $170 each year in temperate climates, such as Sydney, Melbourne and Adelaide.

The Trajectory has been developed cooperatively between Commonwealth, State and Territory Governments, and through extensive consultations with representatives from a range of sectors including: building and property, appliance and technology, energy supply and distribution, environmental, energy consumers, energy efficiency, and academia.

The proposed Trajectory and changes to the NCC in 2022 are expected to be considered by the COAG Energy Council in December 2018. If agreed, approval will then be sought from the Building Ministers’ Forum in early 2019 for the ABCB to commence a formal NCC change process.

When to contact Who?

The NatHERS Administrator receives all kinds of queries in our mailbox. In the 2017-18 financial year around 200 email enquiries were received and responded to. However, the NatHERS Administrator is not always best placed to respond. To understand where to direct your enquiry, a quick reminder is provided below:

 1. Contact the NatHERS Administrator at for:

  • How to become a NatHERS Assessor.
  • Issues for the NatHERS Technical Advisory Committee or NatHERS Steering Committee.
  • Questions about how the Scheme works including accreditation of AAOs, software tool providers or updates to the Chenath Engine.
  • Questions about content on the website
  • Interpreting the NatHERS Technical Note.
  • Reporting of potential breaches of any NatHERS Policies.
  • Feedback or clarification on the content in the NatHERS Assessor Handbook.

2. Contact an Assessor Accrediting Organisation (AAO) for:

  • How to become a NatHERS Assessor.
  • Applying to become a NatHERS accredited assessor.
  • Finding a NatHERS accredited assessor.
  • Questions regarding Assessor Code of Practice and assessor continuing professional development (CPD) requirements/activities.

There are two AAOs currently operating in Australia:

3. Contact your state and territory building authority for:

  • Issues to do with compliance with the building code and/or NCC.
  • Advice on how NatHERS is used for regulatory purposes.
  • Questions about the reference building verification method.

The ABCB lists who the relevant State and Territory Building Administrations are in each jurisdiction here.

NatHERS myth buster: thermal mass

Thermal mass is a material’s ability to heat or retain heat over time and is based on the conductivity, density and specific properties of the material. High thermal mass, like a masonry box, means it is less impacted by changes in external temperature compared to a lightweight timber box.

The thermal mass formulas used by the NatHERS calculation engine (Chenath) were developed from 1953 work by former CSIRO scientist Dr R.W Muncey’s. As you can see in the results below, Muncey’s experiments showed a construction having high thermal mass was less impacted by changing external temperature, both in actual observations and predicted modelling.

Thermal mass is a fundamental element considered in NatHERS software tools. The software calculates how much heat is transferred and potentially generated in a dwelling by considering its orientation and construction (the construction material properties that include thermal mass) combined with occupancy settings, and hourly climate data of its location. This information simulates an internal temperature. If that temperature falls or exceeds the thermostat setting for heating and or cooling, the software triggers a calculation of predicted energy use that would be required to maintain the internal temperature within the thermostat limits.


thermal mass image


View the full paper by Dr R.W Muncey’s work here: The Calculation of Temperatures Inside Buildings Having Variable External Conditions


Your Home

Your Home is a Commonwealth Government funded information source or ‘guide’ to building, buying or renovating a home.

In 2017 ACIL Allen was commissioned to undertake a strategic review of Your Home. This review found that Your Home provides information that can be used by building professionals, including as a means of encouraging behavioural change by consumers who they interact with. This review also found that Your Home is unique and stands apart from other information on home design and renovation. It is a highly-regarded resource and there is unanimous support for government continuing to maintain it.

Based on these findings Your Home is being refreshed, starting with a minor update in 2019 in preparation for major changes in the future. To view the Your Home resource visit


BDAV 2018 Design Awards

The Building Designers Association of Victoria (BDAV) held their annual awards night in August, marking the 23rd year of the BDAV Design Awards. The awards aim to showcase the expertise of building designers and to encourage higher standards of excellence in design. It is open to all BDAV members who are registered building practitioners or registered architects.

An article focusing on the increasing success of sustainable designs at the awards can be found here, and the full list of the 2018 BDAV winners is available on the BDAV website.