Bird-Friendly Design — Part Three: Glazing Solutions
Screens, Grilles, Netting, and Shades
It is possible to attractively combine the benefits of glazing with bird-safe or bird-friendly design by incorporating features that minimize the likelihood of collisions without completely obscuring views.
Some architects have designed decorative facades that wrap entire structures. Recessed windows can functionally reduce the amount of visible glass and thus the threat to birds.
Netting, screens, grilles, shutters, and exterior shades are commonly used elements that can also make glass safe for birds. They can be used in retrofits or be an integral part of an original design, all while significantly reducing bird mortality.
Before the current age of fixed windows, screens protected birds even as they kept bugs out. Several companies sell screens that can be attached with suction cups or eye hooks for small areas of glass. Others specialize in much larger installations.
Netting must be installed several inches in front of the window, so impact does not carry birds into the glass. Screens and nets are still among the most cost-effective methods for protecting birds, and netting can often be installed so as to be nearly invisible.
Decorative grilles are also part of many architectural traditions, as are shutters and exterior shades. These have the additional advantage that they can be closed temporarily, specifically during times most dangerous to birds, such as migration and fledging.
Functional elements such as balconies and balustrades can also act to obscure glazed areas from passing birds.
Awnings and Overhangs
Overhangs have been said to reduce collisions, however, they do not eliminate reflections, and only block glass from the view of birds flying above. They are thus of limited effectiveness as a general strategy.
UV Patterned Glass
Birds can see into the ultraviolet (UV) spectrum of light, a range largely invisible to humans. Patterns of UV-reflective and/or UV-absorbing materials are frequently suggested as the optimal solution for many bird collision problems because they are transparent to humans but visible to birds.
Research suggests that UV patterns need strong contrast to be effective.
Progress in the search for bird-friendly UV glass has been slow, however, owing to inherent technical complexities, and because, in the absence of widespread legislation mandating birdfriendly glass, only a few glass companies recognize this as a market opportunity.
In a study (Klem et al., 2004) comparing bird collisions with vertical panes of glass to those tilted 20 degrees or 40 degrees, the angled glass resulted in less mortality. For this reason, it has been suggested that angled glass should be incorporated into buildings as a bird-friendly feature.
While angled glass may be useful in special circumstances, the birds in the study were flying parallel to the ground from nearby feeders. In most situations, however, birds approach glass from many angles, and can see glass from many perspectives. Angled glass is not recommended as appropriate or useful strategy.
The New York Times printing plant clearly illustrates this point. The angled glass of its primary curtain-wall facade shows clear reflections of nearby vegetation, visible from a long distance away.
Patterns on Glass
Patterns are often applied to glass to reduce the transmission of light and heat; they can also provide some design detail. When designed according to the 2 x 4 rule, (see p. 17) patterns on glass can also prevent bird strikes.
External patterns on glass deter collisions effectively because they block glass reflections, acting like a screen. Ceramic dots or 'frits' and other materials can be screened, printed, or otherwise applied to the glass surface. This design element, useful primarily for new construction, is currently more common in Europe and Asia, but is being offered by an increasing number of manufacturers in the United States.
More commonly, patterns are applied to an internal surface of double-paned windows. Such designs may not be visible if the amount of light reflected from the frit is insufficient to overcome reflections on the glass' outside surface. Some internal frits may only help break up reflections when viewed from some angles and in certain light conditions. This is particularly true for large windows, but also depends on the density of the frit pattern.
The IAC Building in New York City, designed by Frank Gehry, is composed entirely of fritted glass, most of high density. No collision mortalities have been reported at this building after two years of monitoring by Project Safe Flight.
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Current research is testing the relative effectiveness of different frit densities, configurations, and colors.
Opaque and Translucent Glass
Opaque, etched, stained, frosted glass, and glass block can are excellent options to reduce or eliminate collisions, and many attractive architectural applications exist. They can be used in retrofits but are more commonly used in new construction.
Frosted glass is created by acid etching or sandblasting transparent glass. Frosted areas are translucent, but different finishes are available with different levels of light transmission. An entire surface can be frosted, or frosted patterns can be applied. Patterns should conform to the 2 x 4 rule. For retrofits, glass can also be frosted by sandblasting on site.
Stained glass is typically seen in relatively small areas but can be extremely attractive and is not conducive to collisions.
Glass block is extremely versatile, can be used as a design detail or primary construction material, and is also unlikely to cause collisions.
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