According to the IPCC Climate Change projections by 2050 temperatures in southern Spain will have increased noticeably during the summer. Housing—in its current form—will not be able to provide a suitable response to this new climate scenario, and will in turn prompt an increase in cooling energy consumption and a series of problems relating to health and comfort. The Design Builder simulation tool was used to quantify the impact of this future climate scenario on energy demand, as well as its effect under free-running conditions on indoor temperature. Different passive conditioning strategies were evaluated to establish their influence on the indoor comfort conditions. The case study examined a theoretical single-family residential unit model in order to establish guidelines for the pre-selection of the most suitable passive solutions. The results show that passive conditioning strategies analysed (envelope treatment, solar gain protection and night-time natural ventilation) reduce energy demand and indoor temperatures, thus increasing energy efficiency and improving indoor comfort conditions. Therefore, these passive conditioning strategies reduce the cooling energy consumption.