Lightweight envelopes (used primarily for economic reasons) are widely used in modern buildings but their low thermal capacity does not allow an optimal thermal comfort situation to be obtained in summer period. A solution is proposed here by using phase change materials (PCMs) incorporated in building structures to increase their thermal inertia without increasing their volume. A new polymer composite PCM containing 85% of paraffin, with a latent heat of melting of 110 kJ/kg and a melting point at about 27 degrees C, is incorporated in a hollow concrete floor panel. Experimental investigation on thermal behavior is presented to study the response to a temperature variation. Results clearly show the influence of PCM, namely a decrease of the surface wall temperature amplitude and an increase of thermal energy stored. A numerical simulation with COMSOL Multiphysics (R) software confirms the enhancement of the floor inertia by the incorporation of the PCM. The simulation provides design guidelines for the thermal management system to minimize the quantity and size of PCM. (C) 2013 Elsevier B.V. All rights reserved.