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 compliance^2,5.

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 requirements^3,5.

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) categories^4,5.

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.

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 the COLORBOND^® steel colours below for a complete list of the values.

These solar absorptance values are nominal values based on new product. Solar absorptance has been measured in accordance with ASTM E903-96, Standard test method for solar absorptance, reflectance and transmittance of materials using integrating spheres. Solar absorptance is a thermal property and is not suitable for evaluation of visual impacts. For further information refer to BlueScope Technical Bulletin TB 28 - Building Materials, Thermal Efficiency and Reflectivity.

COLORBOND^® steel

COLORBOND^® steel features 22 standard colours inspired by the natural Australian landscape.

COLORBOND^® steel Matt

COLORBOND^® steel Matt is available in five colours to create a softer, more subtle look.

COLORBOND^® Metallic steel

COLORBOND^® Metallic steel is available in six brilliant colours to highlight smart design.

COLORBOND^® Coolmax^® steel

COLORBOND^® Coolmax^® steel with high solar reflectance which may help keep buildings cooler^†.

COLORBOND^® Ultra steel

COLORBOND^® Ultra steel is designed for severe marine environments^#.

SUPERDURA® Stainless steel

SUPERDURA® Stainless steel is designed for very severe marine environments^#.

Note:

• The colours shown have been reproduced to represent actual product colours as accurately as possible. However, we recommend checking your chosen colour against an actual sample of the product as varying light conditions, screens and devices may affect colour tones and finishes.
• We recommend contacting your preferred supplier to confirm colour availability for your selected product and the most suitable material for your project.
• ZINCALUME^® steel is not included in the Tables above. Unpainted metal coated roofs, such as ZINCALUME^® steel, have a low thermal emittance so perform differently to conventional painted surfaces (high emittance) from both an energy efficiency basis and impact upon urban heating. For the purpose of NCC and NSW BASIX ZINCALUME^® steel should be considered a medium colour with SA > 0.45 (per ASTM E1980).
• ^† Compared to conventional roofing materials of lower reflectance index (SRI), such as ZINCALUME^® steel and all other roofing materials in the COLORBOND^® steel range. The extent to which a building is cooler may vary and depend upon the particular circumstances of your building, including building location, level of insulation, location of air-conditioning when installed, building shape, building function and environmental factors. For further information refer to Stockland case study.
• ^# For further guidance on choosing the right product for your project, please refer to BlueScope Technical Bulletins 1A and 1B.