The current trend in the retrofit of existing buildings is to think mainly to environmental aspects, giving few attention to seismic issues. Contrary, recent EU's policies in this field are based on integrated approaches able to improve both energy and earthquake performances of the existing built-up. Therefore, the so-called seismic coats have been launched on the building market. In this framework, the design of a new envelope system, named DUO SYSTEM, for seismic-environmental requalification of existing constructions made of masonry or reinforced concrete is presented and illustrated in the present paper. The novel seismic-environmental coating system is composed of a cold-formed aluminium framed structure equipped with a shear wall system, represented by either OSB panels or aluminium alloy trapezoidal sheeting, which are designed according to the Sheeting Braced Design theory. In the current work, firstly, the novel seismic coat has been presented by detailing all its components. Secondly, the antiseismic solutions based on OSB shear walls have been used for upgrading two existing school buildings, one made of masonry and the other made of reinforced concrete. Finally, the comparisons of performances of examined buildings before and after the intervention have been made to evaluate the benefits provided by the proposed coating system under seismic and environmental viewpoints.