Urban overheating, a phenomenon primarily driven by the replacement of natural materials with artificial ones, disrupts the natural heat balance in both medium- and large-sized cities. In the European Union, approximately 75% of buildings exhibit poor energy performance, leading to increased energy demand for summer cooling. Consequently, the heat released by cooling systems further exacerbates the urban heat Island (UHI) effect, creating a vicious cycle. Numerous studies have shown that Building Integrated Vegetation Technologies (BIVTs), such as green roofs and green walls, can simultaneously reduce building energy consumption and mitigate the UHI effect. Vegetation reduces the solar energy absorbed by building surfaces by providing shade and reflecting incoming radiation. Additionally, evapotranspiration lowers near-surface air temperatures, reducing heat exchange between the air and building envelopes. However, the effectiveness of BIVTs in reducing building energy use, mainly in summer, is influenced by building geometry, orientation, local climate, substrate thickness, coverage percentage, and leaf area index (LAI). This study explores the impact of LAI variations on building energy consumption through detailed investigations of extensive green roofs, green façades, and living walls. Year-round energy simulations were conducted using EnergyPlus software, considering three different LAI levels: low, medium, and high. The simulations were performed for a single residential building in a Mediterranean climate. BIVTs can reduce the annual energy demand by ~ 20% and can be higher when deciduous plant species are used. The results emphasize the influence of LAI on cooling building energy, offering valuable insights for policymakers involved in developing adaptation and mitigation strategies.