The aim of this work is to assess building energy performance optimization potential of cool roof solutions in different climate conditions worldwide through dynamic thermal-energy simulation and optimization analysis. Moreover, given the dependence of roof performance on insulation level, the influence of roof insulation variation on optimum roof solar reflectance is evaluated. Therefore, the multi-dimensional optimization of combined building roof solar reflectance capability and thermal insulation level is carried out to minimize annual energy consumption for air-conditioning of standard ASHRAE building model for small offices, in each considered climate zone. Findings of this research highlight how the classic approach of super-insulated buildings for energy saving needs to be reframed for the office case, by integrating other passive solutions for truly environmentally friendly and comfortable buildings.