This study analyzes the effect of the layout and percentage of sails on the seismic performance of buildings using non-linear static and dynamic analyses. It shows that a wall ratio of 1.0% is optimal for a 7-storey building and 1.5% for a 14-storey building. Beyond that point gains are limited and uneconomical. Centered walls offer better performance than peripheral walls especially when they form complete configurations (U L box). Partial walls reduce stiffness and cause local degradation. The study thus confirms the usefulness of non-linear analyses for optimizing seismic design.