An experimental investigation for determining total equivalent temperature difference (TETD) values of building walls and flat roofs was performed. The TETD values are functions of the time lag, decrement factor and sol-air temperature. The time lag and decrement factor depend on the highest and lowest temperatures at the inner and outer surfaces of the walls or roofs, and the time periods involved in reaching these temperatures. Also, the sol-air temperature depends on essentially solar radiation and outside air temperature. For these reasons, two testing rooms each consisting of four walls and one flat roof, an air conditioner, thermocouples, data logger and a computer were constructed to measure all required temperatures. Inside and outside air temperatures, and surface temperatures of each wall and roof layers were measured in each minute and saved on the computer over a period of 24 h in the summer season of Gaziantep, Turkey. Data for the hourly solar radiation on the walls were computed using hourly measured solar radiation data on horizontal surface. The TETD values for eight different walls and two different roofs commonly used in Turkey were computed by using the measured temperatures and solar radiation flux. The TETD values for the walls and the roofs were also obtained for selected cities in Turkey by utilizing their outside air temperature and solar radiation inputs. (C) 2009 Elsevier Ltd. All rights reserved.