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The greening of façades does not result exclusively for reasons of climate and building design but also from reasons of aesthetics. For example, a façade overgrown with wild vines reflects the individual seasons in the changing colors of its leaves (Figure. 6/8).
Radiation burden from the sun: A façade fully covered by greening is protected from intense solar radiation in summer and can reflect or absorb in its leaf cover between 40% and 80% of the received radiation, depending on the amount and type of greening. If it is so desired that solar radiation reaches the outer wall in winter (cf. Chapter 3), climbing plants that lose their leaves in winter must be used (e.g. wild grapevines, Figute 6/8). Wind conditions: The leaf cover of a green façade changes substantially the airflow conditions on the outer surface of the building. A dense greening produces a calm air cushion next to the outer wall, where the average wind velocity rests below 0.5 m/s. Surface temperatures: The leaf cover changes the balance of radiation at the outer wall. The corresponding air cushion and evaporation also produce a change in the thermal conditions. On sunny summer days the daily temperature amplitude of a greened wall is reduced by up to 30 degrees Celsius in comparison with a non-greened wall. In winter the surface temperature of a wall covered with evergreen plants stays about 2 degrees higher than a non-greened wall. On average, surface temperatures in summer are 1 to 2 degrees lower for greened walls, depending on the orientation of the wall. Heat loss: A façade with a fully-developed, dense growth of evergreen plants exhibits a reduction in heat loss of roughly 6%. This underscores the critical point that a green façade contributes to heating insulation but does not replace an optimal structural insulation! Air humidity inside the greening: Changes in air humidity from greening are as a rule less than may be generally expected. Air humidity is between 2% and 8% lower in winter and between 4% and 20% higher in summer versus a non-greened wall. Hard rains: Green façades represent an effective protection against hard rains. A fully-developed leaf cover reduces the load of driving rain on an exterior wall to zero. In general it is to be noted that façade greening improves the microclimatic conditions around a building itself; however, no long-distance effects are to be expected. Problems are also frequently mentioned in connection with façade greening, especially building humidity and wall damage. In response, the above-mentioned studies found no disadvantageous effect of humidity, but rather spoke of a humidity protection effect on building components via the protection against rain provided by the green cover. Damages from greening are as a rule not to be expected in the presence of intact brickwork and plaster. To what extent a problem can arise for tall buildings from the large biomass required to cover its exterior (i.e. weight on the façade) has not yet been conclusively researched. More information about the various possibilities of outfitting buildings with modern growing techniques, offers the "Handbook Bauwerksbegrünung " (KÖHLER, ANSEL et al., 2012). Legal Bases The controlled greening of building facades has a so far neglected significance for the sustainable, ecological and socio-economic development of towns and cities. But this also entails problems with regard to spatial planning, road traffic and liability legislation and requires regulations concerning the sovereign designation and administrative agreement on the greening of facades (Chilla, T., 2002). Façade greening can be established as legally binding in a site plan in the same manner as roof greening and under the same conditions (cf. Chapter 6.1.4). Example for this type of regulation: "A third of the façade surface is to be greened. Technically founded exceptions can be allowed (§ 9 (1) 25 BauGB)." The option of decreeing localized (i.e. related to building law) construction specifications for the exterior design of structural features according to § 74 (1) LBO remains unchanged. |
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6.1.5 Façade Greening
