Pattern 15: Daylight from Top and Side

Successful daylight from the side begins with maintaining a relationship between window head height and section depth. Generally speaking the effective distance of daylight penetration is roughly two times the head height of the perimeter window. In buildings with traditional floor to ceiling heights this translates to about 20’-0”.

Once an interior section depth exceeds 25’-0” the contrast between perimeter zone and core of the building begins to increase substantially during daylight hours. Since the human eye tends to adjust to the brightest location within a space this can cause the perception of darkness in the interior section, and glare due to the lack of luminous uniformity across the section. There are two primary strategies to address this condition. First, section depths can be kept narrow to ensure both daylight performance and relative uniformity. Alternatively, a second (or multiple) source of daylight can be added to provide supplemental illumination. In this case that source is a horizontal skylight that serves to wash the “back” wall with light and to balance the brightness of the perimeter glazing.

Another common challenge to effective daylighting performance in office buildings is the placement of private offices at the perimeter, with open office areas at the interior. For both energy and social equity reasons, open office areas should be the priority for the provision of daylight. Research indicates that private offices tend to be occupied far less  than open office areas. Furthermore, lighting systems in private offices, if controlled by vacancy sensor, provide little opportunity for photo-controls. Shared open office areas (where electric lights are often on continuously during occupied times and power consumption is greater) provide an opportunity for much higher lighting power savings from daylight responsive controls than private offices. In any event, perimeter private offices preclude effective daylighting to the interior beyond the private office. This remains the case despite the provision of extensive re-lites.

The case study example is the Kitsap County Administration Building in Port Orchard, WA, designed by the Miller Hull Partnership. As appropriate to the prevailing conditions at this site, the simulations show an overcast sky distribution measured lux with the ambient lighting criteria shown at 300 lux.