Introduction The integration of vegetation
Introduction The integration of vegetation on buildings with green façades or roofs allows to obtain an improvement of the building\'s efficiency, ecological and environmental benefits. The environmental benefits of greening the building envelope operate at a range of scale (Perini, 2012). The benefits related to the larger scale (neighbourhood or city) mainly regard the improvement of air quality, urban wildlife (biodiversity), the mitigation of urban heat island effect, and the storm water management (Ottelé et al., 2010; Sternberg et al., 2010; Dunnet and Kingsbury, 2008; Onishi et al., 2010); the ones regarding the building scale concern the building envelope performances and the indoor and outdoor comfort (Dunnet and Kingsbury, 2008; Mazzali et al., 2013; Perini et al., 2011; Kumar and Kaushik, 2005). Green roofs are passive cooling techniques that stop incoming solar radiation from reaching the building structure below. Insulation properties depend on the green roof type (Kumar and Kaushik, 2005). Several properties of green roofs contribute to their thermal characteristics: direct shading of the roof, evaporative cooling from the plants and the growing medium, additional insulation values from both the plants and the growing medium, and the thermal mass effect of the growing medium (Liu and Baskaran, 2003). A vertical green layer can contribute to the building envelope performances by creating an extra stagnant air layer which has an insulating effect (Perini et al., 2011) and reduces the energy demand for air-conditioning up to 40–60% in Mediterranean climate, according to Alexandri and Jones (2008) and to Mazzali et al. (2012), with results which refer to an ideal (adiabatic) room behind the façade. Leaves, thanks also to the phototropism effect, filter the direct sunlight on the façade (Bellomo, 2003). Vertical greening systems can be classified into façade greening and living wall systems (Köhler, 2008). Green façades are based on climbing plants planted directly at the Human FGF21 Protein (His Tag) of the façade or supported by cables or meshes and with planter boxes placed at several heights; for indirect green façades many materials can be used as support for climbing plants such as steel (coated steel, stainless steel, galvanised steel), different types of wood, plastic or aluminium. Living wall systems (LWS), which are also known as green walls and vertical gardens, are constructed through the use of modular panels, each of which contains its own soil or other artificial growing mediums, for example foam, felt, perlite and mineral wool, based on hydroponic culture, using balanced nutrient solutions to provide all or part of the plant\'s food and water requirements (Dunnet and Kingsbury, 2008; Perini et al., 2012). Green roof systems thanks to integrated solutions allow cultivating grass, shrubs and bigger or smaller trees. These are commonly classified in: intensive, semi-intensive and extensive solutions, which have different uses, stratigraphy (substrate thickness) and vegetation (Dunnet and Kingsbury, 2008). The field of retrofitting plays a fundamental role aiming to give more green areas to cities to improve environmental conditions (Frazer, 2005). Buildings consume a significant amount of energy over their life-time; the energy consumption of these in Europe is about 40% of the total energy demand (Thormark, 2002; Ardente et al., 2008). Large scale retrofitting with emphasis on energy efficiency will be needed to reach European standards relative to the 20% reduction (compared to the data of 1990) with respect to primary energy consumption, which generates an output of gases responsible for global overheating (Verbeeck et al., 2008). Many of the vegetation\'s characteristics can be exploited to retrofit, as it will be shown. It is possible to refer especially to the recent built heritage; it often has problems connected to building envelopes un-insulated with also lack thermal mass. This is also the building heritage with the worst architectural value free of cultural and historical limits (Nuzzo and Tomasinsig, 2008).