In this study, time lags and decrement factors for different building materials have been investigated numerically. For this purpose, one dimensional transient heat conduction equation was solved using the Crank-Nicolson scheme under convection boundary conditions. To the outer surface of the wall, periodic boundary conditions were applied. Twenty-six different building materials were selected for analysis. The computations were repeated for eight different thickness of each material and the effects of thickness and the type of material on time lag and decrement factor were investigated. It was found that thickness of material and the type of the material have a very profound effect on the time lag and decrement factor. The results of present study are useful for designing more effective passive solar buildings and other related areas. (c) 2005 Elsevier Ltd. All rights reserved.