To limit the losses due to floods, people can adopt measures to protect their dwellings. We assessed the cost and efficacy of such measures using computer modelling. We found that the benefits of most of the measures studied are unlikely to exceed their cost when they are taken in dwellings that are not exposed to frequent floods (probability of occurrence of less than 1 / 100 per year). It is also often less expensive to use building materials adapted to floods than other common materials.