Roller shutter boxes are facade elements whose acoustic and thermal insulations are a key part of building occupants’ protection from noise pollution and allow a potential savings in energy consumption [1]. Soundproofing insulation of roller shutter box is usually realized using porous and heavy mass panels [2]. The performance of these materials in sound transmission reduction is directly related to their location and thickness. Moreover, the conditions of assembly of the box with other facade elements are of critical importance in its acoustic insulation. In this context, this work focuses on the numerical prediction of the sound transmission loss of a roller shutter box as well as the optimization of the position and dimensions of acoustic insulation materials in order to improve its sound performance. First, a numerical model able to predict the vibro-acoustic response of the studied system is proposed. This model is based on the application of the finite element method for modelling the structure [3, 4] while its sound radiation is calculated by applying the infinite elements method [5]. Experimental results are used to validate the proposed model. In the second part of this work, optimal positions and thickness of soundproofing layers are obtained and discussed. The effect of the position of the curtain, extended or retracted, on the sound transmission, as well as the assembly conditions of the box, are numerically investigated.