The chief principle of this paper is to optimize the location of vertical air space within composite walls based on thermal unsteady response state parameters that include admittance, transmittance, attenuation factor, and time lag. For computation of these parameters, a MATLAB code has been generated. This code solves 1-D heat flow diffusion equation with convective periodic boundary conditions. Six building construction materials such as laterite stone, burnt brick, mudbrick, reinforced brick, fly ash brick, and concrete block were selected and computations were made for 42 configurations of the composite walls. From this, it is concluded that composite walls with air space located at the outer side of the external wall and the mid-center of the external wall are energy efficient from higher time lag, higher thermal admittance, and lower thermal transmittance perspective and the composite walls with air space located at outer and inner sides of the external walls are the best from the lower decrement factor perspective, among seven studied configurations. The results of the study reduce the air conditioning loads in buildings. © 2020, Springer Nature Singapore Pte Ltd.