How to tell if a home is really energy efficient

by | Oct 25, 2022 | Performance

A few months ago, Anthony got the opportunity through Hamish White from Sanctum Homes to host a webinar with the Australian group Builders Declare.   As the industry is preparing for the introduction of a new 7 star energy rating minimum standard in the updated National Construction Code (NCC) that is due for release in September this year, we decided to shine some light on the energy rating scheme and explain what is included in the assessment – and what isn’t.   What you will take away from the webinar:

  • the importance of verifying that a home will perform after construction just as it was intended to in the NatHERS thermal assessment or energy rating.
  • an understanding of how critical it is that our homes are performing as built and not just assumptions in a theoretical energy rating assessment. 
  • learnings on the best practise and what is involved in an as built verification – and how simple it is to achieve. 

You can watch a full recording of the webinar in the video below.

Part 1: Nat what?

NatHERS – or the Nationwide House Energy Rating Scheme – is a software assessment that measures a home’s energy requirements for heating and cooling which is based on almost 70 years of research from the Commonwealth Scientific and Industrial Research Organisation, or better known as the CSIRO.  The software generates a star rating out of 10. The higher the star rating, the less energy is needed to heat and cool the home – and the more efficient it is performing.   The main intention of NatHERS is to reduce the reliance on artificial heating and cooling. Heating and cooling is responsible for the majority of the average Australian household’s energy use and greenhouse gas emissions – which is around 60%. 

Part 2: Thermal camera and blower door tests

A study conducted by Sustainability House determined that thermography and blower door testing are the most suitable as built methods for testing a home’s performance. Which is exactly why we use this method for our own testing with our Outlier Research division.

What is a thermal camera? 

A thermal camera detects infrared energy of objects. The Camera can then convert that energy into an image that indicates the surface temperature. In practice, this means that we can see a variation in temperature, e.g. where insulation is installed – and where it is missing.

What is a Blower Door?

A blower door is basically a giant fan that, when operating, either sucks the air out to depressurise or pumps air in to pressurise the home. As the fan is operating, all the air leaks in your home have air pass through them and they can be identified very easily via touch or with a smoking device.      You can rent and buy both the cameras and blower doors in Australia and there are plenty of helpful instructional videos on how to use them online.    ? Disclaimer: We do perform thermal imagery and blower door tests and if you are interested in booking an inspection with us, feel free to send us a message.

Part 3: The real life experience of energy ratings

We have listened to and had many conversations on the topic of as-built verifications of energy ratings with builders, thermal assessors and home owners and we’d like to share some anecdotes before we jump into the data.    At a recent industry association event, attendees had an open floor to express their views on the transition from 6 to 7 stars for NatHERS assessments. What we heard was pure frustration and a complete disregard towards the energy ratings during construction. It included experiences such as modelling a single window in a room for an assessment but when visiting the site, finding 2 windows and a skylight.  Another story included a window manufacturer ringing a thermal assessor to ask if they should be concerned they had manufactured single glazed aluminium windows when the assessor had modelled thermally broken aluminium double glazed windows. On another occasion, a proud homeowner, shortly after moving into their home, showcased their double glazed windows just to be informed they were in fact single glazing. And finally, a builder was asked by the client how to provide guarantees that the house was built to what the energy rating states. The builders replied that it’s his trade’s responsibility to make sure it’s right. Unfortunately, in our experience, that is not always the case.

Part 4: Misconceptions about the thermal assessment

There might be a misconception that all new homes in Australia require a NatHERS assessment or energy rating with a minimum 6 star (soon 7 star) result. But there are actually 4 methods in our National Construction Code to achieve compliance with the energy efficiency requirements:

  1. NatHERS Assessment Star Rating
  2. Verification against a reference building
  3. Deemed to Satisfy: Achieve all the performance values set in the NCC
  4. Performance Solution: Show how your home is reducing carbon emissions 

According to NatHERS, it is the most popular pathway to demonstrating compliance with the National Construction Code energy efficiency requirements at around 90% for building approvals in 2020-2021 being assessed via the scheme – and around 80% of them being rated at 6 stars.

There are some reductions to 5 star in tropical climates and a couple of states have variations, such as NSW, who have their own assessment called BASIX. We recommend listening to the Builders Declare Podcast episode on Energy Efficiency with Jessica Allen for further information on this. 

The other misconception is that a home is checked during construction to ensure it is being built in accordance with the energy rating. Sadly, this is not a requirement and often does not happen. Crazy right? That minimum 6 Star rating is completely theoretical. 

Part 5: Data doesn’t lie

In our research, ist was mentioned in most studies that the reason the research was conducted was due to concern being raised throughout the industry that new dwellings are not being constructed properly to meet the minimum energy efficiency standards of the NCC.    The research indicated that especially Victorian houses lack in the areas of:

  • Air leakage
  • Ceiling insulation
  • Overall insulation
  • Weather stripping

Air Leakage

A 2015 CSIRO study tested 20 new houses (not older than 3 years) in each capital city around Australia and it was assumed that, given the NCC requirements, they were all NatHERS assessed at a minimum 6 star energy rating or equivalent deemed to satisfy.    The table shows the results of a blower door testing of the homes. In Melbourne, the average result is 19.7 ACH!   There isn’t a single number that NatHERS assumes for air leakage in a home, however, it seems to range from 7 ACH to 15 ACH. Either way our homes are well above the assumed air leakage rates in a NatHERS assessment for 6 stars.

Ceiling insulation

For most homes, physical inspections of the ceiling insulation could also be conducted. It is stated in the report that Melbourne had the highest proportion of insulation with lower R-values, between R2 and R3. The NCC minimum total R-value for a roof in Melbourne’s climate zone is R4.1   Overall the majority of ceiling insulation quality and condition was determined to be average. 

Overall insulation

Wall insulation could not physically be inspected, so thermal cameras were used. The assessment was narrowed to the evenness and coverage of the insulation as well as identifying any gaps in the insulation. Combining the ceiling and wall insulation findings, the table provides an overall result of the homes insulation quality.    The report used the images shown to identify their assessment of poor, average and good quality insulation.    Poor quality   Average quality Good quality

Weather stripping

The report also indicated that external doors and windows weren’t sealed up very well either, with Melbourne homes being rated as average for window sealing and poor for external doors. It might be assumed that this is why we see high air change rates with the blower door testing.

Part 6: Performing an as-built verification

As part of how we perform as-built verifications, we review the plans and the energy rating and make note of any discrepancies. This includes:

  • Identifying the glazing performance values
  • Cross referencing the glazing sizes
  • Identifying the insulation performance values and locations
  • Identifying penetrations such as downlights and exhaust fans

This prepares us for the site inspection, where we will perform a blower door test and use our thermal camera.   Using a thermal camera is a fantastic way to do a final review of the quality of the insulation. Unbeknown to the owner or builder, a trade may have removed insulation for better access to fit off services or lighting and forgot to replace the insulation. A sweep through the home with the camera will quickly identify any defects or missing insulation that can then be rectified.  ? Sustainability Victoria have created a comprehensive checklist on conducting an as-built verification. The methodology has been successfully tested and there are fantastic instructional videos on Sustainability Victoria’s website if you want to perform your own as-built verification.

Part 7: What else can we do?

At Outlier Studio, we include details around airtightness in our construction drawings for new designs and we also specify to perform a blower door test of the home to achieve a maximum 10 ACH.   We include an insulation plan and provide the performance values that are required. Other than that, homeowners or even the builder can request hold points in the building contract that require a certain performance value to be met before proceeding further with the build. An example of this may be that after the plaster was put on, a blower door test must be completed and a result of no greater than 10 ACH must be achieved.

You can call up the verification method in the NCC verification method V2.6.2.3 to verify the building envelope sealing by using a blower door in the contract. Finally, you can use the services of an independent assessor to perform an as-built verification of the home. If you want to use our services, just send us a quick email – we are happy to help! 

Part 8: Why we need as-built validations for energy ratings

Our experiences and the current research show that what is being assessed using NatHERS software modelling is not what is being constructed – and if 80% of assessments are rated at the minimum 6 stars, it is likely that many homes are not meeting the minimum standards of the energy efficiency requirements of the NCC. It is estimated that Australia’s households could generate up to one fifth of Australia’s greenhouse gases. So if we want to reach net zero emissions by 2050, then we need to know how our homes are performing as-built. Studies note that countries that test homes during construction have very energy efficient homes and the quality of construction has increased due to the knowledge gained during the testing of the home. More attention is paid during construction to the details to mitigate air leakage.    Australia needs to almost double the amount of its current housing stock if we are expected to meet the projected population growth by 2050 and with approximately 200,000 new homes being built a year, now is the time to begin verifying the construction of our homes. Also, the less heating and cooling required, the smaller the power bills will be for homeowners. Additionally, as-built verifications  provide a guarantee that the homeowner is getting exactly what they paid for. Finally, a study by the ACT government concluded that homes that are energy efficient see an increase to the property value, so it is literally a smart investment. We need to design and construct homes that provide the performance and environmental outcomes required for us all today – and we believe this can only be guaranteed by as-built verification of a home. 

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