Pattern 5: Glass Area Ratios

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 no more than two times the head height of the perimeter window. In buildings with traditional floor to ceiling heights (~10’) this translates to about 20’-0” of section depth that can be daylit from one side. It should be noted that the configuration and size of interior furnishings, and the presence and use patterns of blinds may substantially reduce this distance.

Once an interior section depth exceeds about 25’-0” (assuming traditional ceiling height) 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, additional sources of daylight can be added to provide supplemental illumination. In this case additional sources are provided in the form of daylight apertures on multiple sidewalls.

The case study example is the 2 Rector Street building in New York City. This pattern sequence highlights simulations under sunny sky conditions during September at noon with workplane illumination data represented in lux. Typical ambient office lighting criteria range from 300- 400 lux and 300 lux was selected as one of the daylighting design criteria examined herein. The percentage of floor area above this value is presented for each permutation.