Urban heat islands explained
The term Urban Heat Island refers to the fact that cities and urban areas are often significantly warmer than rural or undeveloped areas that surround them. The United States Environmental Protection Agency (EPA) reports that on average US cities are up to 5.6°C warmer than the surrounding countryside.
Senior Research Scientist at BlueScope Steel, Jamie Adams, speaks on Urban Heat Islands, what governments are doing and how you can help.
Download video for Windows Media Player 512x288 (33.5 MB) or Windows Media Player 1280x720 (121 MB)
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?
BlueScope Steel Cool Roofs
The Building Code of Australia (BCA) 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 less than 0.35; solar absorptance of between 0.35-0.55; and solar absorptance of more than 0.55 (referred to herein as very light, light and dark respectively). BlueScope Steel produces a range of roof products with low solar absorptance (high reflectance), ?0.55 (Table 1).
Table 1: BlueScope Steel products in BCA low solar absorptance – light colour – categories
Light coloured COLORBOND® steel – incorporating Thermatech® solar reflectance technology – has higher thermal emittance than ZINCALUME® steel, which is not painted. So a light coloured COLORBOND® steel roof 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.
