I live on the Sunshine Coast and am building a double storey house. I was wondering what the temperature difference would be between a Colorbond Windspray roof versus a Shale Grey roof?
Colorbond Windspray has a solar absorptance (SA) of 0.60, which means around 60% of the solar radiation which reaches a roof of this colour will be absorbed. Shale Grey has an SA of 0.44, so would only absorb around 44%, or 16% less solar radiation compared to Windspray.
You are located in NCC climate zone 2, which is a unique climate zone that only occurs on the east coast of Australia, in QLD and northern NSW. It is a cooling load dominated climate ie. it’s primarily about staying cool most of the time throughout the year. I would recommend you select a colour with as low a SA as possible. For instance, Surfmist has an SA of 0.33, which is 11% better again than Shale Grey. You can see the solar absorptance values for all of the Colorbond colours here.
I know you asked about the temperature difference, but this is a difficult question to answer, because there are so many factors that influence the temperature inside a building. We would need to create a thermal analysis model of your proposed design to compare between different roof colours. This is what you can do when you get a NatHERS rating done of your proposed new home.
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