Download the Sustainability Technical Bulletin - Urban Heat Islands - What causes Urban Heat Islands? What are the consequences? And how can we all help mitigate the effects of UHI?

The term Urban Heat Island (UHI) is used to refer to the fact that cities and urban areas are often significantly warmer than the rural or undeveloped areas that surround them. This technical bulletin details why UHIs form; the consequences of UHI formation; and what can be done to mitigate these effects.

Urban forestry and cool roofs are two of the most effective ways to reduce the intensity of UHIs: light coloured COLORBOND® steel with Thermatech® technology can be used to create cool roofs because it has high solar reflectance and thermal emittance.

The Australian Building Codes Board (ABCB) classifies roof colour based on solar absorptance – the inverse of reflectance – expressed as a ratio between 0 and 1. Solar absorptance values are based on as-new/unweathered product. A value of 0 indicates that a roof absorbs none of the incoming solar radiation, whereas a value of 1 would mean that a roof absorbs 100% of the incoming radiation. Three classes have been established: solar absorptance of not more than 0.40; solar absorptance of more than 0.40 but not more than 0.6; and solar absorptance of more than 0.60 (referred to herein as light, medium and dark respectively).

BlueScope Steel produces a range of roof products with low solar absorptance (Table 1).

Category

Light
Solar Absorptance
≤0.40

Medium
Solar Absorptance
≤0.40 & ≤0.60

COLORBOND® Coolmax® Whitehaven®  
COLORBOND® Standard Range Classic Cream™  
  Surfmist®  
    Paperbark®
    Evening Haze®
    Shale Grey™
    Sandbank®
    Dune®
COLORBOND® Metallic Range   Citi®
    Axis®
    Conservatory®
    Skybridge®

Table 1: BlueScope Steel products in BCA low and medium solar absorptance categories

COLORBOND® steel with Thermatech® solar reflectance technology has higher thermal emittance than unpainted metal coated roofs, such as ZINCALUME® steel.  So choosing a light or medium COLORBOND® steel colour not only reduces the amount of solar radiation absorbed, but is also very effective at re-radiating heat. This means that the building will be cooler overall, and cool down faster when the sun isn’t shining, which helps reduce energy demand.

Overall, a light coloured painted steel roof, on a building surrounded by trees – to provide shade and water movement to the atmosphere – is one of the best design scenarios to reduce the intensity and impact of UHIs.

Senior Research Scientist at BlueScope Steel, Jamie Adams, speaks on Urban Heat Islands, what governments are doing and how you can help. View video below.