Space heating is the dominant item of energy consumption of buildings in Turkey. Effective building envelope insulation, especially in early design phase, is the most common passive solution that significantly reduces the annual heating energy requirement of the building. This work aims to assess the effectiveness of additional envelope insulation investments at the early design phase of buildings for all cities in Turkey. The study utilizes the current (2008) and draft 2013 versions of the TS 825 standard "Thermal insulation requirements in buildings". In the study, the effectiveness of insulating an uninsulated building according to TS 825 has been investigated for two different time periods: short term (savings on annual heating energy requirement, additional insulation cost and additional greenhouse gas emissions), and life cycle (life cycle cost and greenhouse gas emissions). In addition, the cost and emission payback times have also been analyzed. Analyzes have shown that insulations based on the standard provides improvements of up to 75% for annual heating energy, 70% for lifecycle cost, and 73% for lifecycle greenhouse gas emissions. Payback periods are under 7 years for the cost and under 2 years for the greenhouse gas emissions.