In Brazil an ambitious target of 24 million new residential buildings are planned to be built by 2022 through a government housing programme titled ‘Minha Casa, Minha Vida’ (My House, My Life in English). The new homes must be thermally comfortable and energy efficient, and hence are expected to comply with the new national energy-focused building regulations. These mandatories Standards, NBR 15220 (Thermal Performance in Buildings) and NBR 15575 (Performance Standard for residential buildings), and also the voluntary Energy Labelling Schemes for Residential Buildings (RTQ-R) are the government set of actions to support the design and the construction of more energy efficient homes. However, although these regulations suggest the need of improving building envelopes as one of the main strategies for providing more energy efficient dwellings, these improvements are based on rather flexible requirements that may not always lead to energy efficient buildings. ‘Fabric first’ is one of the most stringent design approaches to deal with building envelope improvements, focusing on building’s overall energy performance and occupant’s comfort. This approach as a design strategy has great potential to deliver low energy houses in a variety of different climates and its concepts have been incorporated in many buildings across Europe. Despite its success, the benefits of adopting this approach have not been thoroughly investigated in the Brazilian context to date. In this paper, the authors present an investigation of building envelope optimisation based on the fabric first concepts for three cities in southern Brazil. The methodology used sensitivity analysis through the adoption of dynamic building simulations, which were undertaken in order to identify more suitable building fabric combination for the climates considered. These analyses were developed using a parametric approach where a simplified model had its properties changed to evaluate how the envelopes performed as a result of a step increase in the fabric thermal resistance. The findings suggested that moving towards stricter building envelope standards could result in an increase of the number of comfort hours. The results demonstrated that insulated envelopes could increase comfort hours up to 62% when compared to the building envelopes typically adopted in Brazil.