Windows and Sustainability: An Environmental Perspective

May 2007

Educational Advertising Section Provided by Pella® Windows & Doors

Many design strategies can be used to maximize daylighting while reducing glare. Illustration source: LEED-NC Reference Guide. © 2005 U.S. Green Building Council. Used with permission. To learn more about green building and LEED®, visit www.usgbc.org

 

 

Controllability of Systems: Thermal Comfort, Credit 6.2, calls for a high level of thermal comfort system control by individual occupants or by groups in multi-occupant spaces, such as classrooms and conference areas, to promote the productivity, comfort, and well-being of building occupants. Credit 6.2, worth one point, addresses individual comfort levels for 50 percent minimum of the building occupants, to enable adjustments to suit individual needs. Operable windows can be used in lieu of comfort controls for occupants of areas that are 20 feet inside of, and 10 feet to either side of the operable part of the window. The areas of operable windows must meet the requirements of ASHRAE 62.1-2004, on natural ventilation. Comfort system controls for shared spaces should allow adjustments for individual and group needs.

Design strategies to achieve these goals may include the use of operable windows, mechanical systems, or a combination of both. Individual adjustments may involve thermostat controls, diffusers at floor, desk or overhead levels, and radiant panel controls.

 

Hoffman Corporation, an architectural firm in Appleton, WI, incorporated a variety of sustainable strategies in the design of their corporate office. Courtesy of Pella Corporation

 

Daylight and Views: Daylight 75 Percent of Spaces, Credit 8.1, encourages providing building occupants a connection between indoor spaces and the outdoors through the introduction of daylight and views into the regularly occupied areas of the building. Credit 8.1, worth one point, has three options (calculation, simulation, or measurement), all requiring performance in a minimum of 75 percent of all regularly occupied areas.

Courtyards, atriums, clerestory windows, skylights, interior light shelves, exterior fins, louvers, and adjustable blinds used alone, or in combination, are effective strategies to achieve deep daylight penetration. The desired amount of daylight will differ depending on the tasks occurring in a day lit space. Day lit buildings often have several daylight zones with differing target light levels. In addition to light levels, day lighting strategies should address interior color schemes, direct beam penetration, and integration with the electric lighting system.

Glare control is perhaps the most common failure in day lighting strategies. Glare is defined as any excessively bright source of light within the visual field that creates discomfort or loss in visibility. Large window areas provide generous amounts of daylight to task areas. If not controlled properly, this daylight can produce unwanted glare. Measures to control glare include light shelves, louvers, blinds, fins, and shades.

Hoffman Corporation, an architectural firm in Appleton, WI, incorporated several of these strategies in the design of their corporate offices, including:

• Exterior and interior light shelves between the daylight zone and the vision zone
• Clear low-E glass above the light shelf for maximum visible light transmission
• Gray low-E glass below the light shelf to control glare
• White ceilings reflect light deep into the space
• Between-the-glass blinds in the east and west-facing windows block unwanted heat gain
• Triple glazing with multiple low-E coatings reduce heat loss on the north side of the building.

 

 

Daylight and Views: Views for 90 Percent of Spaces, Credit 8.2, calls for providing building occupants with a connection between indoor spaces and the outdoors, through the introduction of daylight and views into the regularly occupied areas of the building. Credit 8.2, worth one point, requires achieving direct line of sight to the outdoors through vision glazing between two feet six inches and seven feet six inches above finished floor for building occupants in 90 percent of all regularly occupied areas. The area with direct line of sight can be determined by totaling the regularly occupied square footage. In plan view, the area should be within sight lines drawn from perimeter vision glazing. In section view, a direct sight line can be drawn from the area to perimeter vision glazing.

Spaces can be designed to maximize daylighting and view opportunities. Strategies include lower partition heights, interior shading devices, interior glazing, and automatic photocell-based controls.

“Building form and orientation can be designed to capture more daylight opportunities. Floor plans should maximize perimeter daylight zones. A standard window can produce useful illumination to a depth of about one and one-half times the window height. The higher the window is placed on the wall, the deeper the daylight penetration,” says Susan K. Oldroyd, AIA, LEED-AP, associate, RossDrulisCusenbery Architecture, Sonoma, CA.

 

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