The main objective of this article is to investigate the influence of the thermal properties of the envelope on the thermal performance of occupied and naturally ventilated houses. A naturally ventilated house built in Southern Brazil was modelled and calibrated in the EnergyPlus computer programme. Based on this calibrated model, a reference model for computer simulations was defined, and variations in the materials of the envelope, occupation patterns and ventilation were carried out. Hourly air temperature and relative air humidity were the output data for the thermal zones of each model. By inputting such data in the Analysis Bin computer programme, the percentage of discomfort hours in the models was obtained. Correlations between the percentage of discomfort hours and the equivalent thermal transmittance, thermal capacity and thermal delay values of the components of the envelope were investigated. Such analysis made clear that there is an influence of the envelope on the thermal performance of the occupied and ventilated house, and that the number of discomfort hours is lower in the models with higher thermal capacity and thermal delay envelope values. It was also observed that thermal capacity was the thermal property with the best correlation to discomfort hours. (C) 2011 Elsevier B.V. All rights reserved.