ROOFING

Many urban and suburban areas have higher temperatures than their rural surroundings. This temperature difference indicates that they are urban heat islands. The annual mean air temperature in a city of a million or more people can easily be 1 to 4°C warmer than in the rural surroundings. On a clear, calm night the difference can measure even 12°C or more. The main cause of urban heat island effect is the modification of the land surface in cities. Natural vegetation is replaced by the built environment. Most surfaces of new structures are characterized by low solar reflectance and high impermeability. Additionally, they are often built with high-density materials which absorb great amounts of thermal energy and release it as heat.

Cool roofs are one of the most effective and easiest solutions to increase the thermal comfort of buildings and reduce cooling costs in hot climate countries with high solar radiation and outdoor temperatures. Brunel University London, in cooperation with the European Cool Roofs Council, Sika Services AG and the University of Technology in Kingston, evaluated a project in Jamaica to study how the application of a solar roof can affect the thermal comfort of residential buildings in hot climates.

Cool roofs are typically covered with white membrane or reflective coating which reflects sunlight. Their energy efficiency can be measured with three main indicators: solar reflectance, thermal emittance and solar reflectance index.