This study considers the link between tertiary buildings design and equipments known as natural and hybrid ventilation or cooling. It focuses on the case of cross ventilated buildings and the envelope choices able to ensure comfort along with energy savings. This link is studied by simulating with TRNSYS various cross ventilation systems: by night, day or both. These are applied to typical situations as individual office, open-plan office, or meeting rooms. Studied rooms are chosen south oriented and subjected to medium internal gains. Thermal behaviour of these rooms is analysed and compared when architectural characteristics vary: insulation level, shading strategy, glassed surface and thermal inertia. These results will be used to develop feasibility criteria for low energy cooling and design guidelines for these rooms for both typical year and heat wave. The case of a complementary mechanical cooling is also studied.