This study provides a comprehensive examination of the effects of building green systems on energy and environmental indicators in Tehran's semi-arid climate. Adopting a mixed-method approach that includes dynamic modeling in EnergyPlus and DesignBuilder software, along with field studies in five sample residential buildings, the research conducts a comparative analysis of four different scenarios. The baseline scenario pertains to conventional buildings without vegetation, while the other three scenarios involve buildings equipped with green walls, green roofs, and a combination of both technologies.

In the methodology section, the base building model was first validated using real energy consumption data. Input parameters were adjusted based on Tehran’s climatic characteristics, including an average annual temperature of 17.5°C, annual rainfall of 230 mm, and relative humidity of 40%. For the green systems, specialized Green Roof and Vertical Greenery modules were used in the software, enabling precise simulation of evapotranspiration processes, insulation capacity, and heat exchange.

Quantitative results indicate that the combined application of green roofs and walls reduces annual energy consumption in the studied buildings by 34.2%. This improvement is achieved through multiple mechanisms:

1. Green walls reduce cooling loads by 40% through shading and improved thermal insulation of facades (lowering the U-value from 1.2 to 0.83 W/m²·K).

2. Green roofs (with 15 cm depth and Sedum vegetation) reduce heating loads by 25% by enhancing thermal resistance (1.2 m²·K/W) and moderating solar radiation (reducing absorption by 45%).

From an environmental perspective, findings highlight the multidimensional impacts of these systems. At the micro-scale, building surface temperatures decrease by 15°C, while ambient humidity increases by 18%. Macro-scale modeling suggests that widespread adoption could mitigate the urban heat island effect in dense areas of Tehran by 2–5°C. Additionally, the vegetation in these systems can absorb 20% of particulate matter (PM2.5) annually and reduce CO₂ emissions by 38 tons per building.

An assessment of implementation challenges reveals an initial installation cost of 15–20 million IRR per square meter and a daily water demand of 35 liters per square meter. However, optimization strategies—such as drought-resistant native plants (e.g., Sedum species), smart drip irrigation, and lightweight structural design—can shorten the payback period to 4–7 years.

A comparison with similar studies in different climates shows that green systems are 15–20% more effective in semi-arid regions than in temperate zones, primarily due to enhanced evapotranspiration and shading effects in hot climates.

In conclusion, the study suggests that integrating these technologies with renewable energy systems (e.g., solar panels) could offer a holistic solution for sustainable building development in the region. Additionally, developing local design guidelines and providing tax incentives could facilitate broader adoption. The findings provide a scientific basis for revising Iran’s national building codes and urban policies.