Pattern 12: Atrium and Adjacent Floorplate

An atrium can serve as an excellent daylighting resource in two-story buildings, however to be successful, several steps are critical. First, the size and shape of the atrium must be designed in relationship to the floor area where daylight is required. Second, the daylight apertures must be designed in terms of size, orientation, and configuration to provide daylight to the critical interior surfaces. Third, the spaces where people spend the most time must be located directly adjacent to the atrium, or within the atrium, so that daylight will reach these areas. Beyond these issues, other critical details include the size and proximity of perimeter daylight sources, location of circulation ways, solar shading and glare control, and light redirecting devices. 

It is of paramount importance that a sober attitude is brought to the design of atriums intended to be a daylighting resource so that the size and shape of the atrium is commensurate with the daylighting task at hand. It is far too easy for atriums to be diminished (narrow throat) by economic or floor area pressures and be expected to solve the daylighting problem for far too great a floor area. With atria design, rules of thumb quickly become inadequate due to the complexity of design interactions discussed above. However a designer must begin somewhere, and a safe (although primitive) rule of thumb to achieve comprehensive daylighting from an atrium is that the atrium should be as wide as it is tall with substantial aperture area in the roof. 

It is important to understand that the success of an atrium for daylighting can be considered in two distinct ways. The first measure of success is an atrium’s ability to provide brightness on vertical surfaces deep within a floor section to help balance the brightness from perimeter windows. Measured in this way, it is relatively easy to have a successful atrium. However, most often designers expect atria to not only increase the perception of interior brightness but to also provide functional illumination on vertical and horizontal surfaces in the spaces within and adjacent to them. Measured in this way, it is far more difficult to achieve a successful atrium. It is this ‘comprehensive’ approach to daylighting design that the rule of thumb above is derived from. It is important to note that both of these goals are important and it is possible to have either one without the other.

This pattern analysis explores the size and shape of an atrium design for a two-story building. It includes an investigation of the width of the atrium, the design of the daylight apertures, and the inclusion of light redirecting elements. The case study used to examine these design alternatives is the Center for Advanced Energy Studies in Idaho Falls, ID. It is a two-story office and laboratory building designed by GSBS Architects. This pattern sequence highlights simulations of the office areas under clear sky conditions during September at noon with workplane illumination data represented in lux. 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 or below this value is presented for each permutation.