**5.1 Selection of paving materials**

Apart from all the afore-mentioned parameters, the overheating of paving materials depends on the geometrical characteristics of the urban open spaces. A preliminary effort to define those "worst-case scenario" instances, namely the instances of urban open spaces where full -or almost full- insolation occurs during the summer months, is presented in a previous study by the author Bougiatioti (2006). The cases of urban canyons with North-to-South direction and with NW-to-SE direction, where the materials of the horizontal surfaces were bound to overheat during the summer, comprise of height-to-width (referred to from now on as H/W) ratios from 0 to 0.5 (or 1). For canyons with NE-to-SW direction, including narrower canyons, have H/W ratio of 1 (or 1.5). Finally, the horizontal surfaces of urban configurations, whose main axis runs East-to-West are prone to overheating in the summer, even in the case of a H/W ratio of 2.

In all the above cases, the negative contribution to the urban microclimate and to thermal comfort is important, and material selection should, thus, aim for:


The application of one or more of the above solutions depends on the character and the use of the urban space, as well as on its design principles. Issues of visual comfort should also be taken into consideration, as the choice of certain materials (i.e. materials with light colours and/or glossy surfaces) can cause glare.

Finally, the materials for urban space should be chosen according to its peculiarities, its character and its patterns of use. During summer days, there should be shaded areas, where the solar radiation is blocked and the surface temperatures of the materials remain low (Khandaker Shabir, 2000). Similarly, during winter and the intermediate seasons (spring and autumn), there should be areas with no obstruction for solar radiation access.
