Air conditioning of building is required to maintain thermal comfort of living areas due to hot and high humid climate in Sri Lanka. Electricity consumption for air conditioners, which are required to operate throughout the year, is much higher, when compared with other electricity usages in buildings. Heat energy transfers to buildings by means of radiation, conduction and convection. As Sri Lanka is a tropical country, roof is exposed to direct sun light in most of the time in a day. Then the major component of heat energy is transferred as radiation through the roof of buildings.