Assessment of Criteria for Residential Buildings’ Insolation: A Comparative Review of European Standards

Sunlight exposure is among the key factors in architectural and urban design. People spend more than half of the day in residential buildings, where sunlight exposure positively affects comfort, well-being, and some health problems. Insolation regulations and recommendations in many countries include criteria for minimum sunlight exposure of interior spaces to meet hygiene and technical standards and to enhance users’ comfort. This research shows a decrease in mandatory insolation criteria for residential spaces in Croatia since the end of the 20th century, which was the motivation for the assessment of European insolation standards. It provides a comparative review of current European recommendations and regulations and addresses the comprehensive issue of residential building insolation through the assessment of planning, urban and architectural design parameters. Research results show that regulatory traditions, climatic conditions, and planning cultures jointly shape national approaches to residential insolation. The research also shows that in the European countries analysed, insolation criteria are mostly mandatory at the national level. The insolation criteria assessed by this research range from urban standards, which refer to buildings, to apartment standards, which refer to rooms. The minimum window-to-floor ratio, with values ranging from 10 to 20%, and the minimum duration of sunlight exposure, with values from 1 to 4 h, were identified as dominant insolation criteria. Sunlight exposure criteria are necessary to protect residents’ hygiene rights, but should be adaptive to socio-economical, cultural and climatic contexts to support sustainable urban development.