Sabu Francis & Associates

This statement is often heard while purchasing an apartment in Mumbai. Such "tips" could be seen in other regions also. How valid are they?

There can never be any golden rule that specifies that a particular direction is the coolest one. Many factors go into making climatically appropriate design. In fact, if there were to be any rule then the West /
South-West direction is more likely to be hotter than any other directions. The reason is to do with two things: a) The declination of the earth and b) The fact that the Sun sets in the Westerly direction.

Declination is the term given to the fact that the axis of the Earth is tilted towards the south. Thus more portion of the South is directed
towards the Sun. It is for this reason, that you can almost never get sunlight coming in from windows on the North side of a building (except for a few mornings in June)

The second aspect (that the Sun sets in the Westerly direction) has some implication for the heat that is built up in a house. Imagine the Sun is your gas stove in your kitchen. What would happen, if you are standing next to it (when it is on, of course) just before you switch off the stove? You would feel the heat on your face, won't you? Even if you have moved away from the fire?

Similarly, the Sun gives its blast of energy into the house just as it sets. Though night may quickly follow, the heat that was introduced just before night will still persist for sometime before it is driven away.