This course is part of the Glass and Glazing Design Academy

Glass is a significant architectural technology featuring versatile applications and the ability to achieve several purposes at once. The multifaceted material is used for transparent glazing in the building envelope to harness natural light and provide views. At the same time, it can incorporate safety characteristics that prevent severe weather or guard against assault—such as intentional breaking in or bullets—from affecting the building and its occupants. Glazing technologies have improved in the form of high-performance thermal systems, which can help building owners hit or surpass sustainability goals. The wide range of aesthetic possibilities make it a unique design element inside and outside, while still being functional on other levels. More recently, in light of a worldwide pandemic, glass offers a solution for homes and commercial buildings to help decrease virus transmission and make healthier, happier spaces for people.

Photo: Geoff Captain; courtesy of C.R. Laurence

Shown is a clear-view glass partition system with a swing door.

Bird-Friendly Glass

There are so many functions that glass can perform in combination with its basic natural-light qualities. In fact, the glass industry is always finding new ways to meet design needs. One example is bird-friendly glass, which has recently become a hot topic in the glass world. According to the American Bird Conservancy (ABC), about 1 billion birds die annually from colliding with public and private buildings. The passive, invisible killer? Clear and reflective architectural glass. Windows of all sizes in both commercial and residential buildings in urban, suburban, and rural landscapes are thought to be invisible to most or all birds due to fly-through conditions, reflected habitat conditions, or a black-hole effect.

A fly-through condition is created when architectural elements provide birds with a clear line of sight to sky or vegetation on the other side. A reflected habitat condition is a condition in which the reflected image in glass is undisturbed and blends with the surrounding habitat (i.e., sky, vegetation). A black-hole effect, also known as a “passage effect,” is a condition in which glass can appear black due to lighting conditions and create the appearance of a cavity or passage through which birds can fly. All of these conditions can create hazardous environments for birds.

Specific buildings may accrue more bird deaths than others due to the large amount of glass and vegetation present. Bird collisions occur throughout the world at all times of day, in every season of the year, and under all weather conditions.

Even just 10 years ago, there was little science for bird-safe technology and very few products available to architects. Over the past decade, however, increased media attention to the issue has attracted the interest of the public as well as building industry professionals such as glass manufacturers, architects, developers, and landscape designers. The demand for bird safety has resulted in many products tested and marketed as bird safe, and research on bird-glazing collision prevention has guided the development of bird-friendly building design.

The key to bird-safe glass is in transforming clear and reflective glazing into barriers that birds will see and avoid.

Image courtesy of Walker Glass Co. Ltd.

The City of Seattle’s Cedar River Municipal Watershed Headquarters located in North Bend, Washington, features bird-friendly glass with acid-etched designs so that birds can identify the glazing and avoid collision.

Solutions and Mitigation Strategies

Creating visual markers: Research has shown that birds begin to perceive buildings and houses as objects to be avoided when the distance between features or patterns on the glass is approximately 11 inches, with the most effective pattern distance at 4 inches edge-to-edge or less. The denser the pattern, the more effective it becomes in projecting itself as a solid object that is perceived by birds. The following glass and glazing products can help minimize bird-related injuries by creating visual markers:

• Etch
• Frit
• Film
• Decals
• Fenestration patterns of vertical and horizontal mullions
• Decorative grilles and louvers
• Artwork
• Ultraviolet (UV) patterns

Making architectural glass safe for birds is a responsible bird-friendly building design practice. The application of markers that are visible to birds and humans or visible to birds only and spaced 2 inches vertically or 4 inches horizontally on the outer pane of a window, with markers ideally located on or adjacent to the outer glass surface, will reduce bird-window collisions. Products following these prescriptive rules repeatedly have been shown to reduce collisions in an effort to help eliminate bird strikes. Products may be tested in order to verify the potential contribution to a bird-friendly design. The results of testing can provide documented third-party results of the threat factor (the lower the better) of a particular glazing solution.

Muting reflections: Muting reflections is an important strategy in glass facade design. Strategies to mute reflections include:

• Angled glass
• Awnings and overhangs
• Sunshades
• Screens, grilles, or mesh
• Shutters
• Louvers
• Window film

Dimming artificial lights at night: The bright artificial lights found in metropolitan areas can attract and disorient migrating birds. In cities located throughout North America, a program such as “Lights Out” may be effective in reducing bird deaths.

Studies have shown that creating visual markers, muting reflections in glass facades, and minimizing light pollution are ways to create more bird-friendly environments. There are a variety of glass and glazing solutions offered by glass fabricators and other stakeholders that will reduce bird collisions.

Legislation and LEED as Drivers for Bird-Friendly Glass

In June 2020, the U.S. House of Representatives passed H.R. 2, the Moving Forward Act, which included H.R. 919, known as the Bird-Safe Buildings Act. The bill mandates that all public buildings managed by the General Services Administration (GSA)—including new construction, newly acquired buildings, and buildings set for substantial renovation—be designed or altered with bird-friendly materials.

There are many exceptions, including buildings on the historic registry, but those that must become bird-friendly require that 90 percent of the exposed facade material from ground level to 40 feet be either not composed of glass or composed of glass with bird-safe modifications. It also requires that at least 60 percent of the exposed facade above 40 feet meet a modified glass standard, that there should be no transparent passageways or corners, and that all glass adjacent to atria or courtyards containing water features, plants, and other bird attractants also meet the glass standard.

Legislation is one way to push for bird-friendly glass. There are also incentives. The U.S. Green Building Council’s Leadership in Environmental and Energy Design (LEED) green building rating system now enables architects, designers, developers, and building owners to earn credit for incorporating design strategies that reduce bird collisions. The credit is currently being tested in the LEED Pilot Credit Library, a rating system development tool that encourages new or innovative green building technologies.

Photo courtesy of Walker Glass Co. Ltd.

Birds can perceive etching on glass and glazing products, which helps minimize bird-related injuries by creating visual markers.