Climate change and its consequences are of a great concern and the likely increasing temperature would add more dilemmas for the choice of passive design options. The performance of building envelopes is one of the key determinants of energy use and thermal comfort. This research presents an evaluation of commonly used construction systems (lightweight and heavyweight) with different levels of thermal mass. The performance of different construction combinations is quantified on the basis of their impact on thermal comfort and energy consumption for current and future time slices in London, UK where climate change impact is expected to be extreme. A flat model is examined as a case study to model the performance of the construction systems with low, medium and high level of thermal mass. The dynamic thermal simulation software used was DesignBuilder, which employs EnergyPlus as its calculation engine. In essence, this study establishes a new approach for assessing the performance of well-insulated contemporary construction systems on the basis of overall annual thermal comfort hours and energy consumption. Results indicate limited advantage of heavyweight construction systems in a changing climate.