An outline is given of basic design principles or natural and hybrid ventilation related to a moderate climate such as in the Netherlands. Experiences from the past should be used to improve the design of naturally and hybrid ventilated buildings in order to improve the confidence in these systems. However, with a better use of buoyancy, wind and sun, the combined pressure-differences can be increased, which will result in a more robust system. The potential improvements of these natural forces are explored with CFD- and mass-flow-simulations. The simulation results of an advanced designed naturally ventilated building are discussed. The results show that the reduction of fan-energy can be substantial which could be applied on low-pressure mechanical ventilated buildings as well. The results of the research can be applied on new as well as on existing, to refurbish buildings.