The global effort to reduce energy consumption generated by buildings involves the increasing use of thermal insulation materials, with expanded polystyrene representing one of the most used materials to this end. The thermal performance of expanded polystyrene has been extensively studied; however, information on the effect of exposure to cyclic environmental conditions on its thermal performance is limited. Therefore, we conducted such a study, which is presented in this article. In the first stage, samples were subjected to 28 days of preconditioning to accelerate the increase in moisture in the material. The second stage involved exposure to 40 freeze–thaw cycles of 12 h each. The weight and thermal conductivity of the samples were measured before and after exposure, and the compression behavior was also analyzed. The results show a decrease in the thermal performance of expanded polystyrene exposed to cyclic environmental conditions, as demonstrated by an increase in the water content of the material under the same measurement conditions and an increase of 5.06% in the average thermal conductivity. The influence of this increase on the thermal performance of commonly used wall construction elements was also been studied and presented in this article. A decrease of 7.59% in the compressive stress of the material at 10% strain was also demonstrated.

A current global effort is being made in order to find solutions that will limit global warming. The building sector is responsible for the highest share of total energy consumption, which requires the continuous development of strategies to increase buildings energy efficiency. Considering the high share of emissions generated by buildings, improving buildings energy performance can significantly slow down global warming. A key point in developing strategies to reduce energy consumption and making more accurate forecasts of the evolution of global warming is to determine the actual energy consumption generated by the use of buildings, which in some cases may differ from the theoretical one. In order to determine the actual energy consumption, with high accuracy, determinations in situ of the thermal resistance of the building elements that form the envelope, are essential. The article presents the main methods for determining the thermal resistance of building elements in situ, factors influencing the accuracy of the results, and recommendations for the use of methods to reduce the risk of errors.