Snow accumulation on glass roofs presents several undesirable consequences. The snowpack both exerts a load on the roof structure as well as hinder the primary function of glass roofs, i.e., to facilitate the transmission of natural light into the interior of a building as well as a view to the outside. Although standards exist for assessing worst-case snow loading on roofs, evaluating natural light penetration through a glass roof requires additional considerations. This study builds on an energy flux-based model for snow cover, here adapted specifically for application to glass roofs. The key adaptations introduced into this model encompass the incorporation of heat transfer dynamics originating from the interior space located beneath the glass roof, along with the implementation of snow sliding phenomena. In addition, the snow cover model also encompasses the modelling of water drainage from the snowpack, as well as the monitoring of snow temperature. When water drains from the snowpack, it forms a low-friction layer between the snowpack and the glass roof. Consequently, under such circumstances, snow is prone to sliding off the roof's surface if it is unobstructed in its sliding motion. The model gives the basis to calculate the light attenuation due to snow based on climate data. The model capabilities are showcased by running it with meteorological data over 30 years for Oslo. The finding from Oslo indicate that light attenuation can be significant during the winter months, that it depends heavily on roof thermal transmittance and if it can physically slide. The usage of high performing glazing can in a no-slide scenario potentially reduce the access to daylight substantially during the months where it can be a scarce resource to begin with.