The orientation of a building is determined by the climatic factors like wind and solar radiations well as by the view it affords, noise and requirement of privacy which may at times override the climatic considerations. The orientation of a building must take into account the amount of solar radiation falling on different sides at different times. However, both radiation and act together to produce the heat experienced by a body or surface. This is expressed sol-air temperature which includes three component temperatures: firstly that of the outdoor air, secondly, the solar radiation absorbed by the body or surface and lastly, the long wave radiant heat exchange with the environment.
By considering the directions of maximum radiant gain for both hot and cold months, it is possible to determine the optimum orientation for any given location. It is difficult to generalise, but as east and west facing walls receive the highest intensities of radiation they should normally be kept as short as possible and openings, if they must be used on these sides, should be as small as possible. The west side, which receives its maximum radiation during the hottest part of the day can be particularly troublesome.
The amount of heat penetrating a building depends largely on the nature of the walls and roof. As air is one of the best insulators, materials which enclose or contain air have low heat transfer characteristics and are generally light in weight. Insulation is most effective under steady state conditions or if the direction of heat flow is constant for long periods.
Walls, roofs and other building components are often made up of two or more layers separated by air spaces which provide a resistance to heat flow. 'he amount of this resistance depends on the width of the air space and the characteristics of the enclosing surfaces. Hence, highly reflective materials like metal foil could be used in air spaces to reduce their Athena conductance by two or three fold.
The principles of thermal control through structural devices, and material use are well illustrated by the way native builders exploit the limited materials available to them and work them into structural forms that admirably meet the demands of climate. To modify the extremes of the diurnal range and to insulate the interior from the blistering heat outside, buildings in hot dry zones are traditionally constructed with thick walls and roofs, and with very small openings. The thick exterior walls and roof often built of materials like clay and stone, absorb solar radiation during the daylight hours and slowly re-radiate it during the night.
In regions where diurnal and seasonal variations are not so large and the intense direct and reflected radiation is the main source of discomfort the wall mass is often reduced with the outside surfaces painted white or some other light colour, to reflect a maximum of the radiant heat. By comas in some areas of extreme diurnal temperature variation, truly monolithic houses are built to increase heat capacity, and in places, are even built into cliff faces or underground.
Although flat roofs are practical in areas where it seldom rains, the great tradition for roofing type in desert regions is the vault or dome, the logic being that as the rounded form of a hemispherical vault has a larger surface area than its base, solar radiation is diluted and re-radiation during the evenings is also greatly facilitated.
In warm-wet regions heavy rainfall and high humidity are combined with relatively moderate air temperature and high solar radiation, so that shade and maximum ventilation are the critical components of comfort. The heat capacity of the structure must, therefore, be as low as possible to prevent accumulation of heat during the daytime, and to minimise
re-radiation, which can cause discomfort at night when air movement is at its lowest. To lessen the heat retaining capacity of the structure and maximise the air flow across the interior, in most areas the wall is reduced to a minimum or eliminated altogether. The roof becomes the dominant element in these houses and acts as a large umbrella; usually of thick thatch and steeply sloped, it both insulates the living space below from the heat of the sun, and allows the torrential rains to be shed quickly and almost silently.
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