Plant Parameters in Green Roofs

High indoor and outdoor temperatures are subjects of concern across the globe. Studies have proven that roofs are the primary component contributing to overheating inside buildings due its maximum solar exposure. This paper reviews plant parameters that could influence the cooling performance of vegetated roofs by studying various typologies. Eight key plant parameters influencing the cooling performance of vegetated roofs have been identified: shading effect of plants, leaf area index LAI, plant evapotranspiration, species selection, plant form, plant physiology, albedo and colour. Studies reveal that shielding effects of plants play a major role in reducing heat gained by roof structures. The presence of dense plants foliage (matured plants with high LAI) creates great magnitude of shadow effects and reduces reflective solar radiation received by building envelope. It is worth noting that rough leaf provides more space on its surface; thus offer better cooling performance. In addition, plant species appear to have different degree of reflectivity; the dark-coloured leaf absorbs the most sunlight energy while light-coloured leaf reflects excess sunlight back to the atmosphere. Hence, roof integrated with dark-coloured plants will be much cooler in comparison. These parameters provide basic source of information with regards to plants selection and integration strategies to be considered when integrating plants on roof for optimum cooling performance.