External shading treatment affects the solar energy incident on a window, and the energy deposited in the room through the window. Since the temperature in a room is dependent on how much solar energy goes into or is lost from the room through the fenestration areas, the walls, roofs and other enclosing surfaces, it would be expected that the modifying effect of an external shading treatment does also affect the inside temperature. This paper presents the procedure for determining such an effect. Two numerical examples are presented. Using the procedure, the inside environmental temperatures for windows with different external shading treatments are studied. The results indicate that the temperature drops with increasing shading depths. The results also show that reveals are by far the most effective shading treatment in the tropics followed by over-hangs. Vertical side-fins are seen to be least effective. (C) 2003 Elsevier Ltd. All rights reserved.