Energy-efficient buildings have received increasing attention in recent times as they represent a direction that promotes the objectives of a sustainable, competitive and decarbonized energy policy. In order to meet the minimum requirements of the nearly zero-energy buildings (nZEB) the thermal characteristics of the envelope play an important role. The aim of the paper is to present and analyse the thermal behaviour of complex joints for an energy efficient school building, for which the formation of thermal bridges has been reduced by applying improved geometrical and technological solutions. Since most of the thermal bridge catalogues did not provide updated details for the studied joints, numerical calculations, as two-dimensional finite elements thermal simulations, were performed to determine thermal transmittance coefficients and the U-value..