The purpose of a building shell is to protect its interior from the ravages of the outside environment. A well-designed building structure should be able to retain heat in the winter and deflect heat penetration in the summer, thus utilizing less energy to heat and cool.

There, cool climates require insulation to contain interior heat while warm climates need protection against the transfer of heat from the warmer exterior to the cooler air-conditioned interior.

To identify the measures for cost and energy conservation,we must examine heat gain, loss and its flow into building. This can be best explained by three basic theories of heat transfer from a warmer area to a cooler area and how it can be reduced:-

c) Radiation

Radiation is the transfer of heat energy in the form of electromagnetic waves, similar to light waves. Thermal radiation is infra-red heat which is absorbed when it strikes the surface of an object. Once the object is heated, it subsequently radiates infra-red rays from its exposed surfaces.

Study has indicated that 87% of heat which flows from roofs is via radiation and only 13% is through conduction and convection. As radiation is the main mode of heat transfer, efforts need to be channelled towards curtailing this heat to ensure a thermally comfortable ambience.

a) Conduction

Conduction is the transmission of heat through materials in direct contact with each other with the heat travelling from a hotter body to a cooler body. Materials which contain trapped air have the ability to reduce the rate of heat transfer by conduction.

b) Convection

Convection is the passage of heat energy by the flow of air. Materials designed to reduce convection will obstruct the free flow of air to the surrounding surfaces.