Solar Absorptance of COLORBOND® steel colours for NCC and BASIX

Sustainable Buildings Research Centre, Fairy Meadow NSW

To recognise the cooling benefit of lower solar absorptance roofing, national and state building regulations have long used it as an energy efficiency design parameter. The 2019 update of the National Construction Code (NCC) has brought changes to the Section J Energy Efficiency provisions for Volume One for roofing material solar absorptance requirements which are further outlined below.

Solar Absorptance

The classification of colours in national and state regulation is based on solar absorptance (SA). SA is the proportion of the total incident solar radiation that is absorbed by the roofing material (the remainder is reflected) and is expressed as a ratio between 0 and 1. A roof with a lower solar absorptance will absorb less heat than a roof with a higher solar absorptance and may help keep the roof space and building cooler on a hot day1.

Solar Absorptance and the National Construction Code (NCC)

Prior to the release of NCC 2019, both Volume One and Volume Two utilised roof solar absorptance as an energy efficiency design parameter in the same way.  With the release of NCC 2019, Volume One has since utilised a different approach to compliance to that of Volume Two, as outlined below.

For detailed information about NCC 2019 Volume One and Volume Two please refer to the NCC website.

Volume One NCC 2019

Volume One of NCC 2019 (regulates primarily multi-residential, commercial, industrial and public assembly buildings and some associated structures) requires the solar absorptance (SA) of the upper surface of the roof be ≤ 0.45 to use the Deemed-To-Satisfy pathway to compliance.  Roof surfaces with SA > 0.45 must use a Performance Solution pathway to compliance2,5.

    Solar Absorptance

    Compliance Pathway

    (Volume One NCC 2019)

    ≤ 0.45 Deemed-to-Satisfy
    > 0.45 Performance Solution

    NOTE: Previously NCC 2016 Volume One had the same requirements as Volume Two.

    Volume Two NCC 2019

    Volume Two of NCC 2019 (regulates primarily smaller scale buildings including houses, small sheds, carports and some associated structures), classifies roof colours as Light (L ≤ 0.40), Medium (0.40 < M ≤ 0.60) or Dark (D > 0.60) based on their solar absorptance values.  Lower solar absorptance values provide for greater concessions in roof insulation R-value requirements3,5.

    Solar Absorptance

    Colour Classification

    (Volume Two NCC 2019)

    ≤ 0.40 Light
    0.40 < SA ≤ 0.60 Medium
    > 0.60 Dark

    NOTE: The solar absorptance classifications used in Volume Two 2019 have not changed from that of NCC Volume Two 2016.

    Colour Classification in Accordance with the New South Wales BASIX

    The New South Wales Building and Sustainability Index (BASIX) has also classified colour into Light, Medium and Dark based on their solar absorptance, however the classification ranges are different to that of the NCC.

    The BASIX classification is Light (L <0.475), Medium (0.475 ≤ M ≤0.7) and Dark (D >0.7) categories4,5.

    Solar Absorptance

    Typical Colour

    (NSW BASIX)

    < 0.475 Light
    0.475 - 0.7 Medium
    > 0.7 Dark

    Solar Absorptance values of COLORBOND® steel

    BlueScope has provided solar absorptance values for 22 standard colours of COLORBOND® steel as well as for COLORBOND® steel Matt, COLORBOND® Metallic steel and more. Please refer to COLORBOND® steel colours for a complete list of the values.


    For further information please refer to:

    Acknowledgements

    Source: BlueScope - May 2020
    Image: Sustainable Buildings Research Centre - Fairy Meadow, New South Wales
    Photography: John Gollings

    Footnotes:

    1. Results will depend on roof colour, level and location of insulation, type and location of building shape and function.
    2. NCC 2019: Volume One, Part J1.3(b)
    3. NCC 2019: Volume Two, Part 3.12.1.2
    4. BASIX Roof colour and solar absorptance
    5. Design parameters are correct at the time of publishing but may be subject to change. Check your local state building regulations at the time of your project.