Journal Article

Visual impact assessment of a skylight retrofit in a heritage building

Ploerer, D, Grobe, L O

2025

Overview

The skylights in the cross-connection hall of Zurich Main Station require replacement due to wear and damage. While safety regulations prohibit new wire mesh glass, heritage guidelines mandate a visually similar alternative. To identify suitable laminated safety glass options, this study combines light scattering measurements, daylight simulations, and luminance analyses. A key factor was the light scattering effect of the original wired glass, which influences the perception of brightness and glare under varying daylight conditions. Measurements using a scanning gonio-photometer quantified these properties for both the historic glass and potential replacements. Single-pane glass samples were optically coupled in a reversible manner to allow for flexible testing. A Radiance-based daylight simulation model was developed to assess the impact of different glass variants on luminance levels from multiple viewpoints inside the hall. The evaluation focused on the percentage of skylight areas that light up under direct sunlight, that is, exceeding luminance thresholds. These are visualized in annual heatmaps. Two glass variants were shortlisted based on their similarity to the original glass in terms of light scattering behaviour. Laminated samples of each were produced, measured, and evaluated to confirm reproducibility. Both options performed well in direct comparison, and the final selection was based on manufacturability and cost-effectiveness. The chosen glass ensures compliance with safety standards while preserving the hall’s historic appearance, demonstrating that a careful balance between heritage conservation and modern requirements is achievable.

• Publisher: IOP Publishing
• Subject: Cost effectiveness / Daylight / Evaluation / Historical buildings / Light scattering / Luminance / Manufacturability / Retrofitting / Safety glass / Skylights / Wire cloth