Pattern 6: Courtyard Depth and Width

Courtyards have been used by building designers to deliver light and air to interior spaces for centuries. The courtyard enables the creation of narrow building footprints under constrained site conditions such as urban areas, and allows for light and air from two sides providing the potential for balanced daylight illumination and the opportunity for cross ventilation.

Understanding the daylight performance of a courtyard building can be complex. Questions that must be answered include: How and when does direct sunlight enter the courtyard? How might program elements be organized around the courtyard to take advantage of light and air while avoiding glare from direct sunlight? How do the interior surface finishes, glazing, aspect ratio and depth of the courtyard shape the nature of diffuse daylight at adjacent visual task areas? How do visual comfort requirements and occupancy times align with solar exposure relative to courtyard orientation and depth?

The inclusion of a courtyard can substantially increase the perimeter area of a building. However, the geometric relationship between the width, area, and depth of the courtyard has a substantial impact on whether adjacent spaces will receive sufficient diffuse daylight illumination, views, balancing luminosity, or all three. In the case of diffuse ambient illumination (sufficient to warrant the inclusion of automated photo-controls for electric lighting) a few common themes emerge. Windows that lie within roughly a 45 degree altitude angle from the sky within the courtyard are likely to substantially benefit from increased diffuse horizontal daylight. Spaces that remain within a 60 degree altitude angle receive the benefit of substantial increased visual brightness from views to the surrounding courtyard surfaces. Below this the contributions of daylight are negligible. These “rules of thumb” of course are malleable within the specifics of climate, building material reflectances, and visual task requirements. These simulation cases are intended to provide clues as to the feasibility of courtyard design concepts.

The case study example is The Terry Thomas building in Seattle, WA, designed by Weber Thompson Architects. The Terry Thomas is a 4 story, 40,000 sq. ft. commercial building.  The courtyard in the as-built condition is roughly 56’-0” by 36’-0” and serves an adjacent floor plate that is approximately 36’-0” deep from perimeter window to courtyard glazing. This provides for a floor plate that meets commonly accepted daylight illumination criteria at 100 percent of the floor plate at the vast majority of daylight hours. One of the primary benefits of the courtyard is to provide daylight form two sides that continuously balances the brightness of the outside perimeter. The Terry Thomas Building uses daylight to reduce internal heat loads from electric lighting during peak cooling times to enable passive cooling. To achieve this goal, no portion of the building is further than 19 ft from a window. Solar heat gains and glare are controlled through active and fixed shading devices. When admitted, direct beam sunlight is confined to circulation ways at the perimeter.