Natural cooling has an important role in decreasing fuel consumption in buildings. The design is mainly directed at reducing heat gains. The following elements are part of the passive precautions taken: window direction, type of fenestration, window surface areas, outside wall construction, inside thermal mass, thermal insulation, shades, and building configuration. The evaluation of these parameters and of natural cooling's feasibility is done by computer simulation. The article describes a computer program devised for this purpose. It calculates indoor temperature variations of typical buildings in the light of the above variables. Found that with natural cooling the typical indoor temperature of a summer day in Istanbul, Turkey (31 Deg. C) could be reduced to 26 Deg. C.