As a key resource-consuming sector, the construction industry faces an essential conflict between initial costs and long-term benefits in its move towards sustainability. Within this paradigm, Value Engineering (VE) is often mistakenly seen purely as a tool for cutting initial capital expenditures (CAPEX). This perspective places it in direct conflict with the capital-intensive demands of green buildings. This research directly challenges that traditional assumption by delineating and validating a comprehensive methodological framework. This framework is designed to synergistically connect three distinct fields: Value Engineering, Life Cycle Costing (LCC) based on ISO 15686, and core sustainability principles (centered on Mabhas 19). Our central thesis rests on the idea that redefining sustainability and LCC optimization as essential, non-negotiable project 'functions' transforms VE from a perceived obstacle into a powerful tool for actually achieving them. To test this framework, we utilized a case study (a virtual laboratory) of a hypothetical residential building in Tehran. The quantitative 30-year LCC analysis provided clear proof that the sustainable design alternatives identified through this integrated VE process, despite carrying a relative increase in initial cost, ultimately led to decisive reductions in total life cycle cost while also significantly enhancing sustainability metrics. These findings ultimately reveal that a proper and rigorous integration of these three methodologies provides a clear, actionable path for achieving optimal, true value-based decisions within Iran's construction industry