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As concerns the current green roofs, finally we included all those roofs matching the above-mentioned constraint on the slope which are categorized as “hoofdgebouw” and exhibit a vegetation coverage greater than 5% of their surface. Based on a thorough visual check to exclude all the false detection due to intense tree coverage, we finally marked as green 1139 roofs. Here, it is worth pointing out that, since there is no agreed definition of what is to be considered as green roof, we applied our criteria following the directions that somehow were agreed in the Antwerp project meeting. In particular, in addition to those roofs where a grass layer or trees have been installed, we also included in the count all those roofs with a consistent presence of hedges or big potted plants (but we excluded those where – based on our experience – their coverage did not look significant enough). Indeed, they as well contribute to absorbing rainwater or reducing the urban heat island effect. Please also note that spontaneously vegetated roofs have been categorized as green roofs only in the cases where the vegetation layer looked significantly thick |