A New Methodology for Successful Daylighting Design

Selecting fabrics for performance shading
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Sponsored by Lutron Electronics Co., Inc.
Jeanette Fitzgerald Pitts

Learning Objectives:

  1. Use performance metrics to quantify the level of glare reduction, daylight autonomy, or view preservation desired on a project.
  2. Explain the relationship between certain fabric properties (openness factor and visible light transmittance) and the shade’s ability to reduce glare, support daylight autonomy, and maintain views.
  3. Specify a shade fabric that will satisfy both performance-based and aesthetic criteria.
  4. Describe how a specification grade shade fabric is different from a typical shade fabric.

Credits:

1 AIA LU/HSW
1 GBCI CE Hour
1 IDCEC CEU/HSW
0.1 IACET CEU*

Imagine a new commercial building situated on a rural stretch of vacant farmland. The envelope of the building is predominantly comprised of large windows on every exposure and boasts a window-to-wall ratio of 60 percent. The intention of the design was to maximize the penetration of soft, glare-free daylight as deeply into the space as possible, saving energy, and providing unobstructed views of the nearby lake and rolling hills that sit adjacent to the site. To that end, an automated shading system was specified to ensure that the shades were always lowered to the most advantageous position. They will be deployed to prevent bright and direct sunlight from penetrating the interior and raised when soft ambient light is available, allowing that usable daylight into the space. Overhead lights can be turned off or dimmed for much of the workday. A beige shade fabric that perfectly complements the interior furnishings was selected.

Upon visiting the occupied building one sunny morning, it is immediately obvious that something has gone horribly wrong. The windows on the eastern exposure are ablaze. The deployed beige shade is backlit to a blinding white by the rising sun, creating an uncomfortable glare across the entire interior window wall. The idyllic view beyond is obscured by the overwhelming brightness at the window. Occupants of the space mention that a similar phenomenon occurs on the western-facing facade as the sun sets.

This tale of window shade woe usually occurs for two reasons: the wrong type of fabric is unknowingly specified onto a project, or, if the right fabric is specified, a fabric that does not meet the specification is delivered and installed, something that happens surprisingly more often than one might think. In either case, the use of an inappropriate shade fabric can be an egregious offense, as it can dramatically disrupt the comfort, productivity, and energy consumption of the interior. This sentiment is echoed by Darrell Sawatzky, senior interior designer, LM Architectural Group, Manitoba, Canada: “Because of its role in daylight and thermal management, and its potential effect on building performance, I believe a shading fabric should be considered as an integral part of the building envelope, instead of a decorative window covering.”

The challenge for specifiers trying to select the right fabric is two-fold. Until recently, the process for identifying the best fabric for a project had not been simple or straightforward. Project objectives are often at odds with one another, like reducing glare, which requires that the shade provide an effective visual barrier between the exterior and the interior, and preserving an outdoor view, which requires that the shade remain as unobtrusive as possible. It is also unclear how various shade fabric characteristics contribute to the overall performance of the fabric, hindering a designer’s ability to tailor the specification of a shade fabric effectively to deliver the necessary performance.

Achieve successful daylighting design by looking beyond the color of the fabric and using performance-based criteria to select a shade.

Photo courtesy of ©Doug Scott 2014

Achieve successful daylighting design by looking beyond the color of the fabric and using performance-based criteria to select a shade.

This article will fill in the information gaps and share specifics on how to select a shade fabric that will meet the daylight management objectives of the space and explore options for ensuring that a conforming shade fabric is delivered and installed onto the project.

Different types of space have different daylight management needs in terms of the degree to which a shade must protect the interior from glare, preserve an outdoor view, and provide thermal regulation.

Photo courtesy of ©Doug Scott 2014

Different types of space have different daylight management needs in terms of the degree to which a shade must protect the interior from glare, preserve an outdoor view, and provide thermal regulation.

 

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Originally published in Architectural Record.

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