Useful notes on the Selection of sites and climate

Before constructing a house, whether in a rural area or an urban area the selection of a good site is the most important prerequisite. In terms of “building or architectural climatology’ the microclimatic conditions are practically more important than the macroclimate of the area.

Microclimatic conditions are influenced by a number of factors such as local relief, nearby buildings, landscaping, existing water bodies and industrial wastes. However, for an efficient site due weight-age should be given to such factors as the bedrock, slope or drainage of the site, cost of the land, and availability of the public utility services.

As regards climatic considerations, the outdoor climatic elements that influence the indoor climate of a building are temperature, wind, precipitation and radiation. In certain cases there are some other weather elements like humidity, cloudiness and visibility which also may be taken into consideration.

Among various weather elements wind is the most important in the selection of a building site. Wind is such a climatic element that produces direct effects on a building. It has the capacity to modify temperature and moisture effects.

In tropical areas which are warm and moist what is urgently needed is the unimpeded free flow of air which may provide some relief from the excessive humidity and high temperatures. In cold climates, on the other hand it controls moisture and increases convective cooling.

In any case, however, as far as practicable the selection of site should be such as to avoid high-velocity winds. In this respect, local relief plays the dominant role in affecting the wind conditions.

In tropical climates with uniformly high temperatures the site selection must give due weight-age to windward slopes, summits in mountainous areas and plains because they receive the full force of winds because of their unrestricted flow.

As we are aware, that mountain slopes and valleys are influenced by air drainage and such local winds as mountain and valley breezes. These local winds are most welcome in summer, particularly in warm climates.

But in winter such local winds are troublesome and produce discomfort. Directions of prevailing winds, if they are from the direction of sources of air pollution, which are many in number, must be taken into account while selecting a site. Wind is the carrier of foul odours, dust, insects and pollens.

In order to modify wind force, temperature and humidity a ground cover should go a long way towards the windward side. If the site has a nearby forest, park or an orchard, the summer temperatures are subjected to their moderating effects.

In case of bare surfaces the temperature extremes are magnified. Buildings constructed in the vicinity of the site selected had their influence on the direction and speed of the winds. Nights during summer months may be abnormally hot in such areas where there are so many large buildings.

The presence of large water bodies like deep and extensive lakes has salutary effect since they minimise the diurnal and seasonal ranges of temperature. Besides, such water bodies induce breezes which modify the temperatures. On the contrary, shallow water bodies do more harm than good by creating enervating high relative humidity.

Sunshine and elevation control the temperature conditions. Besides, the amount of cloudiness influences the atmospheric temperature. Preference should be given to the windward side of an industrial area to avoid the adverse effects of industrial smoke and other pollutants associated with it.

So far as insolation is concerned, it is always advisable to choose a housing site on the equator-ward slopes, if the area happens to be mountainous, where vertical rays of the sun reach the ground giving the maximum benefit from insolation. Contrary to this, the pole-ward slopes are in the shade for part of the day.

In cold countries in the northern hemisphere the eastern and southeastern slopes of the hills and mountains get the maximum sunshine from the morning sun, whereas the west and southwest slopes receive the maximum sunshine in the afternoon.

It is interesting to note that where maximum heating of a building is needed to keep it comfortably warm, westerly exposure is more beneficial than the easterly exposure. The reason is simple.

In case of westerly exposure the insolation is received in the afternoon when the temperatures are highest. Housing sites in deep valleys have a clear disadvantage during the cooler months of the year because they have a shorter period of sunshine.

The elevation of a particular site has a direct effect on its temperature. Places with higher elevation usually have lower temperatures under normal conditions. Such higher places come under the influence of temperature inversion which disturbs the normal lapse rate at night.

During winter when the sky is clear at night the broad valley floors experience extremely low temperatures, whereas the mountain slopes have higher temperatures. Such slopes have the advantage of being above the inversion level and are free from radiation fog smoke or haze.

That is why mountain slopes in cold countries are preferred for health resorts and hotels. High-value fruit orchards are planted on mountain slopes and avoid the broad valley floors.

Even though precipitation does not matter much in the selection of a site, sites, exposed to the wind will be most affected by driving snow or rains. Such sites are to be avoided. While selecting a house site near the river banks, a thorough knowledge of rainfall characteristics of the watershed and the resultant flood regime is essential.

It is undoubtedly true that even the best buildings are not unaffected by weather changes. As safeguards against the inclemency of weather various measures are taken in the construction of buildings such as, orientation of the building, its design and the selection of building materials.

These measures can minimise many of the shortcomings of a site, and can create a suitable climate in and around the house. This is called ‘climate conditioning’ in applied climatology. However, it is always advisable to consider the climatic factor while selecting a suitable site for building a house.