Energy performances and building quality can be achieved by high performance envelopes. In this paper the thermal and mechanical performances of external cladding, applied to a traditional wall, largely used in existing buildings, were investigated by a transient simulation. Result comparison with the thermal performances obtained by simulating the wall without the insulation system showed that external insulation is particularly effective in reducing cooling and heating loads and can also guarantee indoor thermal comfort. Fatigue stresses of the external cladding, investigated by ANSYS simulation, showed that continuous change of the loads over time with limited cyclic stress can cause deterioration of materials. (C) 2007 Elsevier B.V. All rights reserved.