<p>This study implements an integrated framework of fuzzy-based multi-criteria decision-making technique, simulation and experiments for selecting optimal window-to-wall ratios (WWRs) from nine alternatives for vernacular buildings across five distinct climatic zones. A total of ten factors, room temperature, relative humidity, cooling load, heating load, construction cost, comfort index, daylighting factor, CO₂ emission, social acceptability and job creation under techno-economic-socio-environmental criteria, are considered. A model of a vernacular building is created in DesignBuilder and simulated in EnergyPlus to assess thermal factors, while qualitative factors are evaluated based on decision maker input. The results indicate that for composite, hot and dry, hot and humid, temperate and cold climate, the optimal WWR values are 34%, 30%, 34%, 36% and 34%, respectively. Experimental validation confirmed the simulated model’s accuracy with NMBE and CV-RMSE values for factor room temperature and relative humidity falling within ± 10% and 15% set by ASHRAE 14. Investigating the relative importance of factors in the overall selection shows cooling load is the most important factor, while factors under social criteria exhibit the least impact. The implication of the evaluated WWR values in their respective climate shows that the net equivalent electrical energy of the overall architecture ranged between 11,230.6 and 14,529.08&#xa0;kWh, with lowest for the temperate climate, showcasing the effectiveness of selection in that climate. This study shows that the merit of all the factors under any criteria is to be assessed as per their relative importance for the optimal WWR decisions of vernacular architecture.</p>