Evaluating the Effects of Part 19 of Iran’s National Building Regulations on Architectural Envelopes for Reducing Fossil Energy Consumption: A Comparative Study of Residential Buildings in Tehran during the 2000s and 2010s

Abstract

This study aimed to evaluate the effects of implementing Part 19 of Iran’s National Building Regulations on the thermal performance of architectural envelopes and fossil energy consumption in residential buildings constructed in Tehran during the 2000s and 2010s. This applied study adopted a descriptive–analytical, quantitative, and comparative design. The study population comprised multistory residential buildings in Tehran, from which six buildings representing the two construction periods were selected through purposive stratified sampling. The cases were comparable in terms of residential use, climatic conditions, floor area, and number of stories. Data were collected through documentary analysis, field observations, and assessment of building-envelope thermal-performance indicators. The evaluated variables included wall and roof U-values, window-to-wall ratio, insulation type and thickness, glazing and frame type, air infiltration, heating and cooling loads, and annual energy consumption. DesignBuilder and Climate Consultant were used to model and compare each building under three scenarios: a conventional baseline, the existing envelope condition, and an optimized condition incorporating improved insulation, high-performance glazing, shading systems, and more efficient building services. Comparative simulation results indicated that existing envelope strategies reduced annual energy consumption by approximately 20% to 47% relative to the conventional baseline. Under the optimized scenarios, the estimated reduction increased to approximately 49%–61%. The Jamaran Building, characterized by a detached brick screen, extensive vegetation, and double-glazed windows, demonstrated the strongest existing performance and the greatest optimization potential. Buildings constructed more recently generally exhibited lower thermal transmittance, better-controlled window-to-wall ratios, greater use of insulation and double glazing, and higher compliance with Part 19 requirements. Nevertheless, no formal inferential statistical tests, confidence intervals, or probability values were reported; therefore, these findings represent comparative inferences derived from energy simulations rather than statistical hypothesis testing. Part 19 provides an essential regulatory basis for reducing fossil energy use in residential buildings; however, its effectiveness depends on integrated climate-responsive envelope design, rigorous construction supervision, and performance-oriented implementation beyond minimum regulatory compliance.