The interaction between wind and buoyancy in naturally ventilated buildings can lead to multiple steady states. Previous studies have shown that there may exist a stable wind-dominated regime, an unstable wind-dominated regime, and a stable buoyancy-dominated regime. Here we examine the transient evolution of the flow between these regimes as a result of changes in the wind forcing. We show that the transition from the wind-dominated regime to the buoyancy-dominated regime occurs as the wind forcing decreases below a critical value. However, the reverse transition, from the buoyancy-dominated regime to the wind-dominated regime, only occurs if there is a sufficiently large and rapid increase in the wind forcing. We calculate the instantaneous increase in wind forcing required for the system to evolve from the buoyancy-dominated regime to the wind-dominated regime, and we also determine the minimum rate of increase of the wind forcing for such a transition to occur. We discuss the implication of our results for building design.