Bird-friendly Legislation & Code

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:

1. Apply to all new construction, additions, and major retrofits. (See below for more on retrofit requirements.)
2. 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.
3. 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.
4. Include high collision risk auxiliary structures, building structures, and features. Auxiliary structures, including bus shelters, external handrails, wind/noise barriers, and gazebos, among others, also cause collisions. Certain building structures, like building connectors or skywalks, 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.

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.

You will have to decide whether your guidelines apply 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.

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 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 it includes 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.

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 square feet as a threshold under which glass will not have to be bird friendly (a typical sliding glass residential door is 35–40 square feet), 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.

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” in 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!

Often, existing legislation does not apply to all buildings but instead to a subset of new buildings. The subset is frequently defined by, for example, building height, floor area, amount/size of glass, proximity to parks, zoning status (e.g., commercial/residential), or other characteristics or classifications.

Exempted buildings can still cause a lot of collisions because glass is frequently concentrated on the lower floors, where it is most dangerous for birds, and all glass on low-rise buildings is in the primary collisions zone. In fact, buildings under 12 stories tall account for over 99% of collisions, so effective guidelines should not be designed to exempt all but the largest buildings.

Here, we take a brief look at examples of common thresholds used to limit the number of buildings included in bird-friendly legislation.

Some guidelines only apply to buildings that exceed thresholds for building size or the amount of glass — for example, buildings with a gross (i.e., total) floor area over a certain number of square feet (e.g., 10,000 square feet) or percentage of glass on a façade (e.g., 50%). Such limits might sound reasonable, but they essentially serve to exempt small- to medium-sized buildings and buildings that are not entirely glass, no matter their size.

Consider two examples:

First, a typical three-story (~30′-tall) building with a 50 ft x 50 ft footprint. This building has a gross floor area of 7,500 square feet and the entire façade is in the primary collisions zone. Under a 10,000 square feet gross floor area threshold, this building would be exempt from bird-friendly building guidelines even if built of 100% reflective glass.

Second, a 10-story (~100 feet) building with a 150 ft x 150 ft footprint. The total façade area (i.e., building envelope) of this building is 60,000 square feet. If legislation applies only to buildings with over 50% glass, this building would be exempt from design requirements as long as it had less than 30,000 square feet of glass. However, even guidelines that only encourage designers to use less can be positive for birds because they will reduce the total amount of glass in the environment.

These types of exemptions are not what most people have in mind when they advocate for bird-friendly building design requirements. Restrictions like these falsely imply that only large, all-glass buildings are a threat to birds. Bird-friendly building guidelines will be most effective if they focus on the lowest floors of all buildings.

Legislation that applies to new construction (which should include additions), may also include “major renovations.” Predictably, and not unreasonably, there will be concern that a small project, or simply replacing a single window, might trigger the need for a building to comply with the legislation. This should not be the case, and clarity is needed: It is therefore important to specify that in existing building renovations, only major glass replacements fall under bird-friendly guidelines.

Including renovation requirements might not seem worth the trouble, but glass and glass assemblies fail and eventually need to be replaced. Communities are also adopting more stringent greenhouse gas emission limits for buildings, targets that might not be met without new glass. So, there is significant potential to address collisions at existing buildings over time through a major renovation clause. This is important, as legislation in general does not apply to existing glass.

When defining what constitutes a “major renovation,” keep in mind that renovation requirements will only be triggered for buildings that meet your legislation’s other thresholds for inclusion. Consider using language such as: “Renovations that add new glass or replace >25% of existing glass.” Historical and landmarked buildings might be exempted, but most of these do not have much glass.

Some existing legislation only applies to buildings within a fixed distance of a green space of a certain size, or some other measure of bird habitat.

These restrictions are problematic because birds are highly mobile. They use street trees and small patches of vegetation in the built environment, spending time in close proximity to buildings. They also fly from one habitat patch to another, passing buildings along the way. These movements in built environments create collision risks throughout urban areas, as has been documented by window collision monitoring groups in the United States and Canada.

The best choice here is not to restrict bird-friendly design only to areas in close proximity to what is perceived as prime habitat because birds do not restrict themselves to these areas.

While we have documentation of collisions several floors above the 10th floor (i.e., about 100 feet above grade), research shows that collisions tend to be most frequent in areas where glass reflects vegetation. This suggests that the priority area for bird-friendly building guidelines should be the average height of the local tree canopy, perhaps adding as much as 50% – 100% to account for birds flying above trees. This zone is where birds spend most of their time.

Guidelines generally range from 40 feet to 75 feet. ABC’s model ordinance suggests 100 feet. Basically, the higher up the building you go, the more birds you will save!

There are many auxiliary structures and features that are notorious for causing collisions and should never be built out of anything but bird-friendly materials.

In other words, these structures and features should be bird friendly no matter where they occur within a building or as free-standing structures. To view a full list of these features, visit ABC’s Model Ordinance.

High-Risk Auxiliary Structures: Structures that pose significant collision risks to birds wherever they are found. For example:

1. Transparent or highly reflective:
   1. Railings, including balconies
   2. Noise barriers
   3. Wind barriers (including parking structures)
   4. Transportation (e.g., bus stops) or weather shelters
2. Small, stand-alone buildings that present conditions that can be both transparent and reflective and are often located in bird flight paths:
   1. Gazebos
   2. External ticket booths
   3. Any other free-standing glass, plexiglass, or other clear, transparent, or highly reflective free-standing structure, including decorative objects..

High-Risk Building Features: Certain building features are frequently collision hotspots and should always receive special attention, including:

1. Skyways/skywalks
2. Building connectors, no matter the number of floors
3. All outside corners where a bird can see in one side of the building and out the other within 30 feet of the corner.
4. All interior corners within 30 feet of the corner
5. Parallel glass walls ≤50 feet apart
6. Courtyards, including internal atria,
7. Atria
8. Three floors of glazing adjacent to and above green roofs.

Some municipalities have quality view rules that require transparent ground-level windows. The good news is that most types of bird-friendly vision glass provide a quality view, with patterns that prevent collisions covering less than 7% of the glass. There are also a handful of bird-friendly glass products that create patterns in ultraviolet light that some (but not all) birds can see and people cannot, so quality view requirements need not conflict with bird-friendly 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 in legislation is a good idea.

There are a variety of green roof types, from those with short plants like sedges and grasses to a few that can even have trees up to 40 feet tall, although 10- to 15-foot-tall trees are most common. As with vegetation on the ground floor, any glass that is next to one of these roofs will be a collision threat. Green roofs should be included in legislation, even if they are not common yet. All glass adjacent to green roofs should be bird friendly to 30′ above the roof surface.

Vision glass is generally thought of as glass through which people can see the outside world from inside a building. However, this is not the only type of glass that poses a threat to birds. Building exteriors frequently consist of 50% or more of non-vision glass, which is referred to as spandrel glass. For any of a number of reasons, people are not able to see through spandrel glass.

Think of an all-glass building — there are wires, spaces between rooms and floors, and many other building materials that are hidden by spandrel glass so that they cannot be seen from outside. This glass is just as deadly to birds as vision glass, so it should always be included in bird-friendly building guidelines by simply using the word “glass” or “glazing” without specifying a type.