6.2.4    Advantageous Forms of Development

In order for air to flow into and ventilate a city even under weak wind conditions, urban areas should not exhibit too large of a used surface area or building density. Development along the city periphery must not create a blocking belt of structures; it should rather be structured in a loose, open form.
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Hillside Development

For cities in valley and basin topographies, the type and extent of hillside development is of great importance for the urban climate. Development along hillsides should, when impossible to avoid entirely, take place with a measurably low amount of land use, preserving proportionally large unbuilt surfaces and with large distances kept between the individual buildings. Linear development parallel to the hillside creates a substantial hindrance for slope winds. More favorable is linear development vertically down the hillside; although admittedly, this hinders winds running parallel to the slope. Ventilation corridors oriented vertically down the hillside should be kept absolutely open, whereby connected open spaces are to be preferred over spacing areas strewn about and often sealed. Fundamentally, hillside development should remain low and not exceed the height of natural hindrances (e.g. tree heights) in order to ensure favorable flow conditions near the ground. Especially on flatter slopes, point-like development with large green and open spaces helps good ventilation and cold-air production.

Southern slopes are especially attractive for residences. As can be seen in Figure 6/22, development on southerly hillsides is advantageous for energy-saving reasons. In such a planning decision, however, the topographic and climatic aspects referenced above should not be ignored. The development concept resulting from an energy-conscious planning should as a rule not conflict with the interests of the local climate. An example is the decision that narrow valleys, hollows, and cold-air lakes are unfavorable for development under any conditions.
 

Skyscrapers

With a massing of skyscrapers or buildings that tower substantially above their surroundings, the local wind conditions are altered so that the free wind flow is reduced by increased eddying (that is, increase in the vertical wind component at the expense of horizontal wind velocity). From this, a reduction in the wind ventilation of an urban area can result in spite of increased local ventilation or wind turbulence. An extensive higher zone of urban development also has the disadvantageous effect that chimney exhausts of existing buildings are no longer released into the open wind and thus the local air pollution increases despite an unchanged pollution rate. The vertical dimensions of every development should therefore be adapted to the conditions of their surroundings. The planning of skyscrapers requires great care in order to avoid aerodynamically undesired side effects and uncomfortable windy areas. Model studies in wind tunnels (cf. Section 4.2) have proven themselves useful in this respect.

In the Section 3.4.3 you can find hints to the unfavorable nature in energie consumption because they reach zones with higher wind speed and the malfunction ratio between surface and volume.
 

Legal Bases

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	Fig. 6/17: Permeable hillside develop- ment
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	Fig. 6/18: Avoid linear development parallel to the hillside
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	Fig. 6/19: Hillside development with "latch-plate" effect
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	Fig. 6/20: Height of hillside develop- ment
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	Fig. 6/21: Point-like hillside develop- ment
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	Fig. 6/22: Heat losses and temperatures dependent upon topographical situation (Source: BUNZEL et al., 1997)
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