chapter  4
Mitigating the urban heat with cool materials for the buildings’ fabric AFRODITI SYNNE FA ANDM AT SAN TA MOURIS
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Materials used in the envelope of buildings and the urban structures play a very important role in the urban thermal balance. They absorb incident solar and infrared radiation and dissipate a percentage of the accumulated heat through convective and radiative processes to the atmosphere, increasing ambient temperature. Therefore, the use of cool materials on the urban fabric that can reflect a significant part of solar radiation and dissipate the heat they have absorbed through radiation, maintaining lower temperatures compared to conventional building materials, present an effective solution to mitigate urban heat islands. Hence, the technical characteristics of the used materials determine to a high degree the energy consumption and comfort conditions of individual buildings as well as of open spaces. Among the heat island mitigation techniques that have been proposed by researchers, cool materials present some important advantages. They have an important application potential. In most urban areas, about 60 per cent of the urban fabric consists of roofs and pavements. The materials commonly used on these surfaces are characterized by low values of solar reflectance e.g. 0.2 for grey concrete and 0.05 for asphalt. They can be applied on new and existing buildings during renovation in order to avoid additional costs. They are financially viable, as their cost is comparable to conventional materials. The users do not have to change their behaviour. They are environmentally friendly, as they do not add any additional waste – on the contrary, they contribute to the reduction of waste as they prolong the lifetime of the surfaces they are applied to. (Akbari et al., 1992; Akbari et al., 1999; Stathopoulou et al., 2009; Synnefa et al., 2006).