Bird-Friendly Glass

What is Bird-Friendly Glass? 

Glass facades deliver many benefits including daylight, views and dynamic aesthetics. A counterpoint is that birds do not perceive traditional clear glass as an obstacle to their flight path. It is possible to balance glass building benefits with the adverse impact on birds by selecting glass that can take advantage of its many benefits while also minimizing the potential for bird to glass collisions.

Research has shown that adding a pattern can increase a bird’s ability to perceive glass, thus reducing the likelihood of a collision. This awareness has lead organizations, cities and states to develop bird-safe building guidelines, laws and official standards that apply to architectural glass and buildings.

Viracon's Involvement

As a glass fabricator, Viracon has been actively involved in the ongoing bird friendly glass research, focusing specifically on finding practical solutions using conventional glass products for buildings with applied patterns. Additional information about the research and testing is available in the Tech Talk.

The Tunnel Test

Birds are released into one end of a test tunnel. They fly toward the opposite end of the tunnel where there is an opening with a clear control sample and a test sample with a pattern. Birds respond by flying toward the control sample or the test sample as they attempt to exit the tunnel (light netting is installed in front of the glass to prevent collisions with the glass). Researchers record each flight and study the response to score the test sample. The score for the sample is the percentage of birds tested that fly towards the clear glass (American Bird Conservancy 2012).

  Viracon's Bird-Friendly Glass Tech TalkClick the link above for more information on our tested products, as well as patterns that meet The American Bird Conservancy's Prescriptive Ratings for bird-friendly glass.

Product Scoring and Threat Factors

Scores from the ABC tunnel test are utilized by ABC and the U.S. Green Building Council® (USGBC) to assign a threat factor for each tested material. A lower threat factor means that the product deterred more birds in the tunnel test than a product with a higher threat factor.

Threat factors are a key component in comparing bird deterrence products and in achieving the bird collision deterrence Innovation credit in the LEED® for Building Design and Construction rating system. Designing a façade where all materials have a threat factor of 30 or less means the project is exempt from additional calculations. If any material with a threat factor >30 is used, then Bird Collision Threat Rating (BCTR) calculations are required (U.S. Green Building Council 2019).

Prescriptive 2x2 Pattern Rule: Threat Factor 20

The 2x2 Rule indicates developing patterns with lines or shapes spaced no more than 2” apart can deter collisions.
(American Bird Conservancy Prescriptive Rating Guidelines for Bird-friendly Materials 2023)

Overall glass assembly must meet all to comply:

• Exterior Reflectance of the overall glass assembly (excluding visual markers):  <=15%
• Any color of opaque ceramic frit/ceramic ink
• Clear, mid-iron or low-iron glass
• Patterns on surface #2 with the low-e coating behind the pattern
• A pattern that is made up of one of the following elements:
  • Continuous solid lines at least 1/8” wide, no more than 2” apart measured edge to edge.
  • Circular, square or irregular solid shapes no more than 2” from another shape measured horizontally or vertically edge to edge. Each shape must have 1/4” (6mm) diameter minimum.

Prescriptive 2x4 Pattern Rule: Threat Factor 25

The 2x4 Rule indicates developing pattern with horizontal lines or other shapes spaced no more than 2” apart or vertical lines spaced no more than 4” apart can deter collisions. (American Bird Conservancy Prescriptive Rating Guidelines for Bird-friendly Materials 2023)

Option 1: Surface #1 Acid Etch Patterns 

Option 2: Surface #2 Ceramic Patterns 

Prescriptive <2” Spacing Rule: Threat Factor 25

(American Bird Conservancy Prescriptive Rating Guidelines for Bird-friendly Materials 2023)

Overall glass assembly must meet all to comply:

• Exterior Reflectance of the overall glass assembly (excluding visual markers):  <=15%
• Any color of opaque ceramic frit/ceramic ink
• Clear, mid-iron or low-iron glass
• Patterns on surface #2 with the low-e coating behind the pattern
• A pattern that is made up of one of the following elements:
  • Continuous solid lines at least 1/4” (6mm) wide and spacing equivalent to line width, measured edge to edge, up to < 2”.
  • Circular, square or irregular solid shapes at least 1/4” (6mm) diameter, with spacing between shapes no less than diameter of pattern elements and no more than 2” measured edge to edge.