Urban mesoclimate is formed by a multitude of factors enhancing climate change characteristics like increasing temperature levels, reduced air moisture content, atmospheric pollution or extreme rain events. All of these factors could be attenuated by green roof structures. Unfortunately, this potential is not being tapped in current building practice. The majority of erected green roofs are built as extensive, i.e. non-irrigated, types. This results in a poor mesoclimatic impact as the water contents of these roof substrate layers are meagre, and vegetation layers are more or less inactive during the dry, hot summer months. Intensive green roofs, on the other hand, require higher load-bearing capacities and costs, both often not eligible for refurbishments. A promising approach is a combination of simple intensive green roof structures featuring a thin substrate layer with reduced irrigation techniques, especially under the usage of grey water. The hygrothermal performance of these structures in comparison between different irrigation schemes and solar radiation levels is shown in this article. Measurements were performed over a period of about two years. Hygrothermal performance shows the importance of an optimised relationship between irrigation scheme, substrate type and thickness in order to achieve a sufficient evapotranspiration and temperature balancing effect.