Glass Collisions

Creating Bird-Friendly Legislation

Vassar Bridge Science Building, N.Y. ©Christine Sheppard

The Specifics of Bird-Friendly Building Ordinances

Bird-friendly legislation in the U.S. started in 2008 with then-local Congressman Mike Quigley's bill for unincorporated Cook County, Illinois (excluding Chicago). Since then, dozens of jurisdictions, from states to towns, have passed legislation.

Bird-friendly design ordinances generally include the same sections, including which structures are covered, how much of each structure must be bird-friendly, and how “bird-friendly” will be defined. Within these topics, however, there has been considerable variation. We have learned that while specifics may sound similar, they may actually be quite different — and there have also been unintended consequences. Below, we review each section and provide links to additional information, calculations, and other specifics.

American Bird Conservancy (ABC) has created a model ordinance that can be quickly summarized as 100/100/100: 100% of new buildings should be built using 100% bird-friendly materials in the first 100 feet above grade.

ABC's Model Bird-Friendly Ordinance

Download ABC's Model Ordinance to use as a template for your community.


Many bodies and groups considering such guidelines will be interested in softening the language to exempt certain types of buildings or to reduce the amount of bird-friendly glass required in an effort to make compliance easier. If that is the case for you, we recommend beginning with our draft ordinance because it includes accurate definitions and the main issues to be considered, then revising it until it is agreeable.

Which Buildings Should Be Bird Friendly?

Most bird-friendly building legislation applies only to new construction. In some cases, it also includes renovations that change a significant portion of a building's glass. Historic and landmarked buildings are often exempted. No current legislation requires existing buildings to change glass that was not otherwise intended to be replaced (and this should not be a requirement, as it would be very expensive to do this).

Some options to consider including within bird-friendly building legislation include:

a. Apply to all new construction, additions, and major retrofits. (See below for more on retrofit requirements.)
b. Apply to a subset of new buildings. Legislation would only apply to buildings that meet some measure of height, floor or wall area, amount of glass area, or other variable. Because collisions are concentrated in the first 50-100 feet of all building types, this type of legislation exempts much of the most dangerous glass.
c. Apply only to structures ‘near' or within perceived priority bird areas. These can be green spaces and water bodies of certain sizes, habitat corridors, Important Bird Areas, etc. This strategy is problematic because birds are highly mobile, use even small green areas, and fly from one area to another, passing dangerous glass along the way. It is unfortunately very easy to use a priority area clause to exempt a majority of hazardous buildings.
d. Include high collision risk auxiliary structures and building structures and features. Auxiliary structures, including bus shelters, external hand rails, wind/noise barriers, gazebos, etc. also cause collisions. Certain building structures, like building connectors or sky walks, should also be called out for extra attention because they can be collision hotspots. These can all be hazards but are often omitted because they are not understood to pose a risk. They should be required to be bird-friendly no matter where they are found.

Should Guidelines Consider the Whole Building or Individual Façades?

You will have to decide whether your guidelines are applied to entire buildings or if buildings are first broken down into sections. There are two options:

1) Target the combined walls of a building (the “envelope”) as a whole (e.g., 75% of the building envelope must consist of bird-friendly materials), or
2) Consider each façade (i.e., “side”) separately (e.g., 75% of each façade must be bird friendly).

No matter which option is chosen, the guidelines will then require that a certain percentage or minimum area meet a bird-friendly threshold or standard (more below). The glass in the zone where birds are most active should always be the priority. Ideally, this would be from the ground to 100 feet, but most ordinances do not go this high.

Which of these options is chosen can impact how effective legislation will be, so pros and cons must be carefully considered, especially as other stakeholders in the project may have different goals and concerns.

It is better to create requirements for individual building façades than for entire building envelopes.

Targeting the envelope as a whole can be problematic without safeguards because this allows designers to stack all of the permissible non-bird-friendly glass into a single, dangerous area that may even be an entire side of the building.

An example illustrates the difference. Consider applying an ordinance that requires that 75% of the building envelope be bird friendly to a row of buildings. Such buildings frequently have three walls that are bird-friendly because they have little to no glass on the sides or back… but they then have a single large wall consisting almost entirely of dangerous glass. Using a building envelope approach of 75%, the three bird-friendly sides allow all of the non-bird-friendly materials to be stacked on a single, untreated side that poses a serious collision risk.

On the other hand, instead of applying to the building envelope, consider if the ordinance required that 75% of each façade were bird friendly. The three sides with little glass would still be bird friendly while the fourth all-glass side would then be required to use at least 75% bird-friendly glass, thereby doing a better job of meeting the spirit of the ordinance.

In some cases, people might argue that non-bird-friendly glass should be consolidated for an atrium or lobby. However, there are now highly effective bird-friendly glass options with patterns that cover less than 7% of the glass, so it is possible to provide a bird-friendly atrium that uses glass, is heavily planted, and still has quality views to the outside.

Care should be taken that whatever is selected will work for the different types of buildings that will be covered.

Should Requirements Apply to Only the Glass or Consider Glass as One of Many Building Materials?

Another question is whether the glass is considered separately or as one material among others comprising the envelope. It makes a big difference whether you require that 75% of the glass to be bird friendly vs. requiring that 75% of the envelope be bird friendly. LEED Pilot Credit #55: Bird Collision Deterrence is based on all façade materials. The credit gives double weight to glass on the first 40' of the building and provides a calculator to generate a weighted average by area of the Threat Factor values of the materials comprising the envelope.

Requiring a percentage of the glass is always safe because you ensure that the glass itself must be bird friendly. On the other hand, requiring a percentage of the envelope to be bird friendly can mean that no glass needs to be bird friendly.

Consider guidelines requiring at least 75% of a building to be made of bird-friendly materials. This means that 75% of the building can be made of stone, wood, brick, and any materials that are not a collision threat, while the remaining 25% is exempted, even if dangerous reflective glass. While this is certainly better than a building that is 50% or 75% dangerous glass, that 25% can still cause a lot of collisions and would be much better if it were bird-friendly. If, on the other hand, the requirements stated that 75% of the glass must be bird friendly, then even in a building with only 25% glass, the majority of it must be made bird friendly.

Also take into consideration that your selection here interacts with the other decisions that you make, such as selecting the building envelope or individual façades.

Will You Exempt Panes of Glass Under a Certain Size?

Another important question to answer is whether there is a maximum allowable area for a single pane of non-bird-friendly glass. In other words, does your ordinance state that pieces of glass under a certain size do not have to be bird friendly?

There is no easy answer here because even small panes of glass can be a threat to birds. The small birds that are the most frequent collision victims can and will fly through very small spaces. So, while smaller panes are safer, they alone are not sufficient to prevent collisions – especially when many small panes are placed side-by-side. Developers will advocate for the largest minimum panel size possible as a way to exempt as many buildings/as much glass as they can.

Several cities have settled on 20 ft2 as a threshold under which glass will not have to be bird friendly (a typical sliding glass residential door is 35-40 ft2), but that is still a huge piece of glass for a bird with a seven-inch wingspan. This also excludes essentially all home windows, where almost 50% of collisions occur. For homes, most small areas of glass can easily be made bird friendly by installing external insect screens, but this is not usually a solution for larger structures with glass curtain walls.

The best answer here is to include all glass regardless of pane size and, if a pane-size threshold must be included, to make it as small as possible.

All glass, even if it is insulated, transmits heat more readily than do other façade materials. When glass represents above 20- 40% of the envelope, depending on climate, heating and cooling costs start to rise significantly, making the building less sustainable and more expensive to operate. So, make sure you start by discussing energy efficiency and then talk about making the remaining glass safe for birds.

How Will Bird-friendly Materials Be Defined?

There are several ways to define acceptable materials. Some legislation includes multiple options to allow architects the freedom to design novel solutions, while making it easy to find a simple product for a minor job.

ABC defines bird-friendly materials as those with a Material Threat Factor less than or equal to 30. All commercially available materials with Threat Factors can be found in our database of Products and Solutions.

In Canada, some jurisdictions specify that bird-friendly patterns must be on the outside of the glass, on “side 1.” Side 1 materials are preferred because on the outside, surface reflections will not obscure most patterns. However, this type of glass is not yet readily available. Other materials can also work well, and many architects are not comfortable with specifying side 1. Stricter standards will protect more birds but provide greater compliance challenges.

"Prescriptive" options provide a set of criteria, based on existing research, that define acceptable glass, including spacing, opacity, color, orientation, and minimum dimensions of pattern elements, along with surface reflectivity, glass color, and presence of coatings. Pattern elements (lines, dots, etc.) should have no more than 2″ separating them with solid lines at least 1/8” diameter and non-lines at least ¼” in diameter. Remember that external structures like screens and louvers should be included.

ABC's Model Ordinance has recommended language that defines a large universe of bird-friendly glass for you!

Other Questions

Some bird-friendly building guidelines are optional/voluntary while others are mandatory. The reality is that voluntary guidelines will seldom be followed, so mandatory guidelines are the better option.

Some municipalities have quality view rules that require transparent ground-level windows. The good news is that many types of bird-friendly vision glass provide a quality view, with patterns that prevent collisions covering as little as 1% of the glass.

Glass adjacent to green roofs is frequently included in bird-friendly glass requirements, regardless of a building's height or size. These roofs attract birds, even in the most urban settings, so including green roofs is a good idea. A common recommendation is that the two floors directly adjacent and above a green roof should use bird-friendly materials. For large green roofs, this is probably not sufficient.

Additional Information

There are many additional nuances surrounding the language used in bird-friendly building guidelines. If you would like to find out more about the specifics of writing guidelines, please explore Learn More: Bird-friendly Legislation, which covers more details.

Still have questions? Contact ABC's Glass Collisions Program.

Take Action for Birds

ABC is working hard to make federal buildings bird friendly. Join us today and ask Congress to pass the Bird-Safe Buildings Act!

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