Extensive roof greenery questioned

Abstract

EN: The green roofs are mostly seen as architectural components having a positive influence on quality of life, particularly in urban settlement structures. This positiveeffect is manifested at the macro level through improving air quality and also reducing effectcalled urban heat islands and at the very buildings by raising their interior comfort, especiallyfloors directly under the roof. The precondition for effectiveness at macro level is particularlyhealthy green converting carbon dioxide to oxygen, casting a shadow on the flat roof andmoisturizing surroundings in the summer. In the winter, it has particularly aesthetic andpsychological importance. The care of greenery is of paramount importance, while in larger areasit may also be quite costly affair. The operation of green roofs may over time exceed possibilitiesof small investors, which is then reflected in a gradual decline of greenery and counterproductivechange of the roof into a dusty surface with negative impacts in the environment .A correct design of greenery reflecting the roof structure and location of the building is therefore very important. In terms of the quality of the internal environment the greenery itself is more or less nonsignificantfactor, a more important role plays the substrate, which can contribute to the thermalprotection of the internal environment in the summer and winter as well. In summer, it isespecially its ability to accumulate solar radiation and thus prevent overheating of the under-roofspace. In winter time period, the substrate is contributing to the improvement of thermalresistance of the roof structure, even though it has to be ignored within calculation of the roof’sthermal resistance as it is not its integral part. From legal point of view, hence, an improvedthermal protection of under-roof spaces is a secondary effect of the green roof and as such should not play a major role in the decision-making process during the green roof design (even thoughin case of wooden roofs it can be quite an important factor). More important is to consider whether the cost of its construction and operation will return in the form of more attractive and healthier environment, but this is easier said than quantified.