Impact of glazed balcony design on daylight in Finnish apartments

Sustainable dwellings should prioritise designs that prevent early obsolescence by supporting occupant needs, their comfort and wellbeing. This includes the provision of good indoor environmental quality and adequate and usable private spaces, including balconies. Yet, visual comfort is still overlooked, specifically in Finland, with its added balcony glazing, its northern position and Nordic climate. This study examines how different glazed balcony designs affect daylight in Finnish apartments. It explores how orientation and geographical location affect daylight performance seasonally considering balcony depth. The research methods include: (1) in-situ daylight factor measurements supplemented with observations and residents' interviews in 10 Finnish case studies; and (2) seasonal assessment of daylight availability and visual comfort using parametric simulations of a selected case study in four orientations, three geographical locations and with three balcony depths. Findings reveal that while balcony depth directly impacted daylight availability, balcony glazing had little effect unless daylight was already scarce. Good daylight generally occurred only in shallow-plan layouts with dual orientation, or when unobstructed by a balcony. Minimising room depth can compensate for the daylight-reducing impact of the balcony. A balance of daylight access, privacy and solar overexposure is needed. PRACTICE RELEVANCE New insights from this study offer guidance for better balcony and apartment design. Key recommendations include the following: (1) Optimise balcony and room depth to maintain daylight access. In single-aspect designs without additional windows, balcony depth should be reduced to compensate for the daylight-reducing impact of the balcony. (2) Balcony design should be adapted to geographical locations, e.g. in highlatitude regions such as Finland, shading from balconies offers limited benefit due to the low solar angle, hence other strategies should be prioritised to mitigate summer solar overexposure. (3) Daylight considerations should be integrated with spatial planning, prioritising daylight-sensitive spaces such as kitchens while ensuring privacy for spaces such as bedrooms. Daylight metrics need integration with user feedback for holistic design decisions. Although the findings cannot be generalised based on a single tool, the authors suggest further development of simulation tools to better address the impacts of glazed balconies.