Efficacy of Korea’s Diagonal Plane Restriction for Daylight: Focusing on South-North Direction Blocks within Seoul’s General Residential Districts

Since the beginning of the 20th century, daylight access-related regulations have been an integral part of urban development. The Diagonal Plane Restriction in South Korea is one such regulation. This paper evaluates the effectiveness of the policy by investigating buildings in General Residential Districts in Seoul and the factors that have influenced its success. First, selected buildings were analyzed based on their relative core locations, massing morphology, and the glazing proportions on the south elevations. The initial results showed that nearly 50% of the selected buildings had cores on the south side, thus limiting daylight infiltration to the habitable spaces with a glazing ratio under 30%. Secondly, binary logistic regression was performed between identified types and variables to identify the primary factors affecting the ineffective arrangement. The year of a building’s construction and its primary use can significantly predict the effective applicability of a restriction. Lastly, further descriptive analysis shows how policy changes directly contributed to the growth of low-performing types and commercial uses in residential districts. The results of this study point to the shortcomings of urban policy-making without considering the particulars of each urban context. Our findings could assist planners and policy-makers in redesigning regulations for ensuring optimal daylight access in residential districts.