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ROOFING

Building roof colours should be light – medium colour (as per the BCA definitions) rather than a dark colour, to help mitigate the effects of the Urban Heat Island effect.


From the BCA 2019 Volume 2 Part 3.12.1.2 Roofs Explanatory Notes item 6: 

A low Solar Absorptance (SA) roof reduces the flow of heat from solar radiation better than a high solar absorptance roof. A roof with a solar absorptance value of less than 0.4 typically corresponds to a roof of light colour such as white, off-white or cream. Typical absorptance values based on ASTM E903 are as follows:

Colour - Value - BCA Classification

  • Slate (dark grey) - 0.90 - Dark

  • Red, green - 0.75 - Dark

  • Yellow, buff - 0.60 - Medium

  • Zinc aluminium — dull - 0.55 - Medium

  • Galvanised steel— dull - 0.55 - Medium

  • Light grey - 0.45 - Medium

  • Off white - 0.35 - Light 

  • Light cream - 0.30 - Light

Note solar absorptance values above 0.60 are considered dark.

Colorbond Steel provides Solar Absorptance values for its roofing to comply with BCA requirements


Alternatively the Solar Reflective Index (SRI) of roofs can be considered for the same effect. From the Green Star Design and As Built Credit 25 the SRI should be greater than an initial figure of 82 or three year minimum of 64 for roofs of pitch less than 15 degrees, and 39 initially or three year figure of 34 for roofs with a pitch of greater than 15 degrees.