Several single zone, monthly based, correlation methods have been developed at a national level , ver the past few years. Although the application limits of those methods are mostly unclear or unknown, the tendency grows to promote at the international level, such correlation methods as basis for simplified thermal calculations in the design process. The validity of a single zone, monthly based, correlation approach is analysed for residential building types in different european climate zones. Methods: Through numerical simulations with the CEC-reference model ESP, and using 5 european Test Reference Years Copenhagen, Lerwick, Brussels, Milano, Trapani a parametric analysis has been performed on different construction and building types. Simulation results are compared with calculations which follow the draft EUROCODE methodology, the IEA annex XII methodology, and the french Method 5000 methodology. A sensitivity study was undertaken with regard to ?environmental parameters, building parameters and heat transfer mechanisms, in the scope of energy and comfort performance assessment. Results and Conclusion: Detailed results are reported in the paper. However some of the main conclusions are : if the objective is to predict energy and comfort in a building within a 15% accuracy band on a yearly base, then a unique correlation curve can not be derived for the wide variety of european climate zones, building types and building operations, when adopting a single zone correlation method;The transmission losses are strongly dependant on the net radiation balance (shortwave/longwave), especially in the Mediterranean area. Therefore assumptions about boundary heat-exchange phenome na (global/splitted h.e.-coeff., fixed/free convection coeff.,absorption/emission) are extremely important together with the choice of control temperature and control strategy. This paper contains also several indications for future design tool development, badly needed by the design profession.