Last update: 28.10.2020
Building with glass

Bird-friendly glazing

The use of glass in architecture with its transparency and reflectivity can influence the perception of the environment.

What’s the problem?

The use of glass in architecture with its transparency and reflectivity can influence the perception of the environment. 
Unlike humans, birds are not able to perceive images reflected on glass surfaces as a reflection and hit the glass, which appears like a cloudy sky, a tree or other natural environment.

Transparent glazings are also dangerous, as birds do not perceive it as a solid object and strike the glass to try to enter the environment visible behind it. In particular, glazed corridors, windows behind each other, glass walls, glass balconies and all-glass corners are critical.

The impact in full flight often results in death. The problem is getting worse as cities are growing and the use of glass in architecture is expanding. Authorities and investors in Central Europe and North America have recognised the problem and many glass manufacturers have developed products and technologies to address the problem.


What’s the problem-_Reflections


What’s the problem-_Transparency


Evaluation of „bird-friendly“ solutions

When the awareness of bird collisions on glass became established by planners and users, the glass industry started to develop glazings accordingly to minimise the effect, but no standards or regulations were availabe to verify so-called bird friendly or bird protection glass solutions.

The first step was the introduction of the Austrian standard ONR 191040. This standard describes the effectiveness of solutions and „bird-protection glass“ was first time established in assessments and regulations. It evaluates the glass solutions through special tests using a “flight tunnel“. Two glazings are placed next to each other at the end of the tunnel: one standard reference glass and one glass with bird protective measure to be tested. A defined number of birds are set free and fly in the direction of the glass. In order to prevent the birds hitting the glass, a net is placed in front of the glazings.

To consider a glazing as bird-friendly, less that 10 % of the test birds must decide to fly into the sample glass with the protective measure. This 10 % limit was agreed with Swiss, Austrian, German and American ornithologists. Based on experiments with thousands of birds, 4 categories of effectiveness were defined:

A    highly effective     < 10 % approach
B    limited         10 % to 20 % approach
C    poor            20 to 45 % approach
D    not effective        > 45 %

The topic of bird-protection is currently under discussion and the knowledge of the behaviour of the birds and suitable glass products are continously developing. 

Glass solutions providing better visibility for birds

In general, the following rule applies: the higher the visible contrast the better. On large glass areas without grids, lower reflections are favourable, as landscapes are less visible. Very high reflections can even interfere with non-transparent markings. Right now, the common meaning is accepted that light reflection values < 15 % (applies for triple glazing too!) do not require an opaque marking. Organisations such as the BUND (D), the Ornithological station Sempach (CH) or the Minergie Certification (CH) recommend exterior reflections of < 15 % as “low-priced and reasonable solution“ without obstructed views. The Minergie organisation states for windows generally “maximum of 15 % (better 12 %), particularly if trees/bushes are in front of the glass“. Façades should have markings or a limitation of the exterior reflection < 15 %, corner glazings of 2 m or larger should be performed always with markings.

For higher requirements, an additional marking should be applied at least on surface #2 of the glazing. An ideal solution, if architectural SunGuard solar control or ClimaGuard thermal insulating coatings are involved, is the enamel “System TEA“ for ceramic printing of black marks directly onto the coating. As this enamel dissolves the coating (and it’s reflection) a maximum contrast can be achieved when looking from outside on the glass.

For any markings, the maximum distance should not exceed 10 cm and the diameter of the single marks (e.g. dots) should not be less than 8 mm. It’s not the degree of coverage that is crucial, but the maximum contrast when looking from the exterior!

Critical constructions (e.g. corners, glass walls, balconies or glass walk-ways) require the marking outside on #1. According to current knowledge in Europe, UV marking is considered as „poorly suitable“ or even „not effective“. 

Looking for birds friendly glass?

Each year, millions of birds accidentally fly into glass windows, doors and facades, with many of these collisions being fatal. As glass continues to make up more and more of the external building envelope, it is likely that the number of birds affected by this problem will increase over the coming years.