The potential for passive cooling of roof slabs incorporating an air cavity is important with respect tothermal comfort. Roof systems in traditional buildings, incorporated a ventilated roof or an air cavity.The concept has been proposed again in contemporary buildings in the construction of roof slabs,using a modular formwork system, where the cast in situ concrete slab is isolated from the screed with the introduction of a ventilated air space. The cavity is primarily intended to curtail the conduction and inward radiation of heat from the intense solar insolation on the concrete roof. An experimental investigation was conducted for summer and winter conditions, where a traditional monolithic slab and a slab incorporating a cavity were analysed. Results indicated that during the cold season, a ventilated cavity looses more heat to the outdoor environment, and is ideally unventilated. It was revealed that in summer the ventilated cavity reduces heat transfer in the flat roofs, improves comfort conditions and potentially reduces the overall cooling load. A strategy for further research on the thermal performance of ventilated flat roofs is proposed, based on further laboratory investigation, and the monitoring and assessment of buildings.