Residential and commercial buildings consume approximately 20% of the global energy generation. This value is continuously growing and the governments across the globe have realized the importance of regulating the building construction to optimize the energy utilization. Energy efficient building codes have been developed to optimize the energy efficiency in buildings. OTTV (Overall Thermal Transfer Value) is a key parameter for evaluating energy efficiency of building envelops in the present building code of Sri Lanka. In this research, the prescriptive requirements mentioned in the building code for the building envelops to optimize the energy efficiency of five (05) commercial buildings has been analyzed. The indoor climate was modeled and the annual cooling energy variation with Overall Thermal Transfer Value was studied using “DesignBuilder” software. A cost benefit analysis was carried out for enhanced energy efficiency building envelops applications. It was attempted to develop a general relationship between the OTTV and annual cooling energy requirement for each building. It has been observed that a second order polynomial relationship with R2 of 0.861 exists for RDA building, linear relationship with R2 of 0.838 exists for AirMech building. However a specific relationship could not be observed for BMICH, SLSI and WTC buildings. The impact on cooling energy requirement from envelop parameter modification is unique for each building. In some instances the reduction of OTTV has not resulted in any reduction of the cooling energy requirement. There is a combined effect from each building component which affects the final cooling energy requirement. A simulation based technique to be used to find the optimum building envelops design.