More than 40% of energy consumption in Iran associated with the building sector. Among the factors affecting energy consumption, time lag and decrement factor of the walls can be mentioned, which usually are not considered in the design of building of Iran. Therefore, in the present study, time lags and decrement factor for different building materials that prevalently are utilized in Iran have been investigated. In this research, the transient heat conduction equation is solved analytically using Green function under time-dependent convection boundary conditions. The effect of different parameters such as wall thickness and both inner and outer heat transfer coefficients as well as the effect of the thermal insulation layer in sandwich wall on time lag and decrement factor is investigated. The results indicate that the thickness and the type of the building material have a significant effect on the time lag and decrement factor of the wall. Also, it is shown that inside combined convection and radiation heat transfer coefficients affects time lag and decrement factor of the walls. The results of the present study are applicable for designing more effective passive solar buildings in Iran and optimal design of walls and other related areas resulting in energy saving. (C) 2017 Elsevier Ltd. All rights reserved.