Cool roofs help maintain thermal comfort and minimise energy demand in buildings as well as reduce the intensity of Urban Heat Islands
Cool roofs have high solar reflectivity, and preferably, high thermal emittance
High solar reflectivity means that less energy is absorbed into the roof initially, thereby reducing the amount of energy that can be converted to heat and re-radiated as longwave radiation.
This reduces the heat that can move from the roof to the atmosphere by convection and conduction and limits the amount of longwave radiation available to heat the atmosphere. The surface temperature of a cool roof can be up to 39°C less than a dark coloured roof.
High thermal emittance means that any energy that is absorbed into the roof is re-radiated from the building quickly once the sun sets (again increasing thermal comfort and minimising energy demand).
There are also potential benefits for building owners beyond a reduced energy bill. Limiting the quantity of absorbed solar energy and reducing daily temperature fluctuations – which cause repeated contraction and expansion – can extend the life of the roof.
BlueScope Steel Cool Roofs
BlueScope Steel produces a range of roofing products with high solar reflectance that can be integrated into designs to improve thermal comfort. The solar reflectance of COLORBOND® steel for roofing has been improved due to the addition of Thermatech® solar reflectance technology to all 20 standard COLORBOND® steel colours at no additional cost to consumers.
A light coloured COLORBOND® 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.
This blog post has been sourced directly from the Bluescope Steel Sustainability Website. We have published the article without making any change to the original piece.
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