A one dimensional heat transfer model for periodic outdoor conditions is presented and used to evaluate the thermal performance of a monolayered and multilayered envelope wall/roof in an air-conditioned and in a non air-conditioned room Three materials are tested for a monolayered wall/roof high density concrete (HOC) aerated concrete (AeC) and expanded polystyrene foam (EPS) Three multilayered walls/roofs of width 0 10 m composed of a sheet of 0 02 m of EPS and the rest of HOC are considered The EPS can be on the outside middle or inside of the wall/roof The main conclusion is that an appropriate wall/roof for an air-conditioned room may not be suitable for a non air-conditioned one For the monolayered wall/roof and conditions under study it is found that in an air-conditioned room the most important physical property of the wall/roof is its thermal conductivity which has to be as small as possible while for the non air-conditioned room the most important physical property is the thermal diffusivity which also has to be as small as possible In this case the position of the insulation in a multilayered wall/roof is important (C) 2010 Elsevier B V All rights reserved