Designing low-energy buildings has become a necessity, encouraged by thermal regulations, the need for energy savings and environmental awareness. Computer-aided thermal design of building walls is currently investigated using the latest optimization algorithms. This paper studies building multilayer walls by coupling a direct thermal model with a specific optimization algorithm. The direct problem solution is based on the Laplace transform of the quadrupole method, and then translated by numerical inversion into the time domain by the Fourier series method. The optimization model minimizes a least squares criterion between intended indoor temperatures and a direct response model. The work aims to optimize the thermal insulation and the heat capacity of wall layers and further building heating loads. An indoor temperature evolution is specified under fixed outdoor conditions in order to identify the composition of the building walls using an inverse resolution based on a reflective Newton algorithm applied to a direct quadrupole model. (C) 2013 Elsevier B.V. All rights reserved.