In this study, the effect of outdoor absorption coefficient of an opaque wall on time lag, decrement factor and temperature variations is investigated by employing a dynamic thermal-network model. The model simulates heat transfer by conduction through the wall and considers convection boundary conditions under detailed forcing functions on the wall outer and inner surfaces. The transient analysis is based on the fundamental principles of thermal circuits and the well-known analogies between the thermal and electrical laws are employed. The effect of the solar absorptivity, is examined for representative wall formations including masonry, insulation and coatings on both surfaces. The insulation is placed as one or two layers on the outer, the inner or in the mid-center of the masonry. The investigation is carried out for a wall with south orientation during the cooling season in the Mediterranean region. The analyses presume a non-sinusoidal periodical excitation that simulates precisely the effect of the outdoor environmental conditions. Computer results show how these varied aspects affect thermal inertia parameters and outdoor/indoor temperature peaks. (c) 2006 Elsevier B.V. All rights reserved.