This paper presents the bioclimatic characteristics of vernacular houses in Mardin City and a quantitative evaluation of parameters affecting energy efficiency. For the evaluation; the parameters of site, settlement density, optical and thermo-physical properties of the building envelope are covered. An existing house representing vernacular Mardin housing is selected and modelled with the surrounding settlement. The simulation is performed for a typical meteorological year. Five different cases are modelled to evaluate different parameters and simulated to calculate monthly heating and cooling energy demands. The results reveal the significance of each parameter for contributing to energy efficiency. The base case representing the existing settlement has been determined as the optimum case with minimum total energy demands though the results vary when heating and cooling demands are considered separately. Energy demands are strongly affected by thermo-physical characteristics but especially the use of massive materials in the envelope (up to 39.77%). Settlement scale parameters of site and settlement density change balance of heating and cooling demands but in total have limited influence on total energy loads. (1.79% and 1.52%) Increasing window to wall ratio from 4.88% to 10% have increased yearly total energy loads by 2.05%.