A simulation-based review of the ubiquitous window-head-height to daylit zone depth rule-of-thumb

This paper reviews the validity of the ubiquitous daylighting rule of thumb (DRT) that relates window-head-height to the depth of the daylit area adjacent to a facade. Different versions of the rule taken from prominent daylighting design guides and norms are presented. A formal link is established between the depth of the daylit zone and the simulated daylight autonomy distribution in a space. Based on this link daylit zone depths of rectangular sidelit spaces are simulated using Radiance for a variety of climates, facade orientations, facade geometries, and usage patterns. Simulation results largely support predictions made by DRT for standard design variants. At the same time they demonstrate the limitations of the rule and promote daylight simulations as a natural complement to the rule if more advanced daylighting systems are investigated.