Star Rating Misconceptions
The National Construction Code
The National Construction Code (NCC) sets out minimum standards for energy efficiency depending on location and climate zone.
Part 3 of Volume Two of the NCC allows for two general methods of compliance for house:
The elemental provisions option can be followed to meet minimum standards regarding things like wall and roof total R-values, glazing standards, and details such as thermal breaks.
The energy rating option allows for a rating under the Nationwide House Energy Rating Scheme to prove compliance.(ABCB, 2016)
In unique cases, compliance can also be achieved through a third path called a performance solution or a deemed to satisfy solution.
The Nationwide House Energy Rating Scheme (NatHERS)
The Nationwide House Energy Rating Scheme (NatHERS) rates houses with a star rating out of ten. Modelling software simulates the thermal performance of the home’s design, orientation, and materials, based on long-term average hourly weather data from the Bureau of Meteorology for the specific location. The underlying simulation engine is developed and maintained by the CSIRO.
“A 0-star rating means the building shell does practically nothing to reduce the discomfort of hot or cold weather. A 6-star rating indicates good, but not outstanding, thermal performance. Occupants of a 10-star rated home are unlikely to need any artificial cooling or heating.”(NatHERS, 2018)
This means that it’s easier to achieve a higher rating in a milder climate and vice-versa.
💡 The difference between stars is not lineal, for example, in Canberra, where an 8-star home is predicted to use half as much energy for heating and cooling as a 6-star home.
NatHERS does not take into consideration embodied energy or energy used to run appliances or heat hot water.
Minimum requirements vary by location. Most states and territories legislate a minimum of six stars, while New South Wales uses the BASIX system that specifies maximum heating and cooling loads rather than a star rating.
💡 Working with a collaborative NatHERS energy assessor will help you optimise the R-values depending on your project, climate and budget, and avoid diminishing returns. Cooee projects involve an energy assessor on every project as a non-negotiable.
Building Sustainability Index (BASIX)
The NSW government have their own rating system for residential dwellings, called the Building Sustainability Index (BASIX). This is an online tool that anyone can use. It provides an assessment of thermal comfort, water efficiency and energy efficiency, including for appliances. The thermal section of BASIX is less sophisticated than NatHERS but the tool covers a wider spectrum of elements, providing a more holistic valuation. NatHERS modelling can be used for the thermal section of BASIX.
Voluntary Tools
It’s important to be critical when choosing a voluntary rating tool to use as these vary significantly in method and philosophy.
Living Building Challenge – An international certification based on a broad philosophy across seven performance petals, including site, water, energy, health, materials, equity and beauty. Certification is based on actual performance, rather than predicted. It’s arguably the most rigorous rating tool. (International Living Future Institute, 2018)
Passivhaus - Originates in Germany and shouldn’t be confused with a passive solar design approach. To be accredited, houses must meet specific measurements regarding extreme airtightness and low heating and cooling energy use achieved through high levels of insulation and thermal breaking. (Passive House Institute, 2018)
Where to find more
The information above is extracted from my book, 101 Things I Didn't Learn in Architecture School; And wish I'd known before my first job.
While the book is written for students and graduates of architecture, it is also an excellent handbook for anyone embarking on their own project. We provide a free copy with every on-site briefing and feasibility meeting, or you can purchase your own copy here.
Another great resource on basic principles in Australia is the YourHome.gov website which is free to access.
Building scientist, Jenny Edwards, maintains a useful blog at www.lighthouseteam.com.au
References
Australian Building Codes Board. 2016. National Construction Code 2016 – Volume Two. www.abcb.gov.au/-/media/Files/ABCB-NCC/NCC_2016_Volume_Two1.pdf.
Nationwide House Energy Rating Scheme (NatHERS). 2018. “Home Energy Star Ratings.” www.nathers.gov.au/owners-and-builders/home-energy-star-ratings.
*International Living Future Institute. 2018. “Living Building Basics.” https://living-future.org/lbc/basics/.*
Passive House Institute. 2018. “Passive House Requirements.” passivehouse.com/02_informations/02_passive-house-requirements/02_passive-house-requirements.htm.