Heat gain in building is best resisted by
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Answer:
Heat is gained by roof, walls and windows by exposure to solar radiation. Sun rises in east and sets in west. It moves southwardly. In winters its altitude is lower and the sun rays enter a house through a window. In summers its altitude is higher and it it is prevented by the sunshade (Chajjas) to get entry inside a room from a south facing window. So south facing window is best in tropical country like India.
East facing wall gets heated up in the morning up to solar noon and west facing wall faces sun from noon to evening. North gets only diffused sunlight.
But the ROOF gets solar radiation through out the day. It means that the maximum heat gain is by ROOF only. It is about 50% of the total heat gain. This absorbed heat travels through the roof or walls by conduction.
Hot air intrudes through the windows if they are open. Means it travels by convection. But a closed window can be heated up by itself and can transfer this heat by radiating it from the inner surface. Double glazed window with cavity retains the heat and prevents its transfer to inner side.