Date: 30 October 2020
When designing a building, architects must strike a balance between form, function, and very real budget constraints. Adding to the challenge, more and more municipalities are now requiring bird friendly products, which can increase project costs. Fortunately, architects can minimize costs related to bird safe glass design rules with smart decisions in the planning phase.
Selecting Quality Bird Safe Glass
Architects today have a number of bird friendly glass options to choose from, possessing various qualities and price points. Field studies and tunnel testing show that the most effective design solutions comply with the 2” by 4” rule. This rule requires markers no more than two inches apart on a horizontal axis, or four inches apart on a vertical axis.
These dimensions are shorter top-to-bottom than most birds in flight and narrower than their wingspans. Even though birds don’t see the glass itself, they see the markers as tightly-spaced obstacles. As a result, the birds don’t try to fly through the glass.
Extensive testing has shown that the most effective markers are placed on the outside surface of the outboard lite (surface #1). Surface #1 is important because it’s the only one which is always visible, regardless of lighting conditions.
Glass can appear either transparent, reflective, or very dark, depending on light conditions. Because of this, markers placed on interior surfaces are far less visible in certain lighting conditions and birds won’t see them. Unfortunately, many bird friendly solutions fall into this category. This is not the case for acid-etched glass.
Acid etching remains permanently on the glass surface and, unlike ceramic frit markers, doesn’t add extra layers which may fade or wear off over time. Since they’re embedded in the glass, acid etched markers will not degrade or lose their effect, even when exposed to the elements. However, acid etching is factory-applied to glass stock sheets, not to cut-to-size openings. Without proper window design planning, a significant amount of the stock sheet can be wasted. The key is to maximize the usable cuts from each sheet. Here are some bird safe glass design rules to make that happen.
Walker produces 96” x 130” sheets of bird friendly glass, with 1” of loss on each edge. As a result, the usable dimensions of each sheet are roughly 94” x 128”. To make the best use of the glass, fabricators input all required lite sizes into an optimization program that lays out the best cutting sequence for each sheet.
If the architect designs windows (less framing) that are 47” wide or narrower, the fabricator will be able to cut two or more sheets of glass side by side from the sheet. This minimizes the amount of waste. On the other hand, if the window panes are wider than 47”, then the fabricator will only get one lite out of the sheet and the rest of the glass will go to the recycling bin.
By keeping the 94” x 128” limitation in mind, the architect can use the glass most efficiently, and help keep the project price down.
Walker also produces bird friendly etched glass sheets measuring 72” x 130” or 84” x 130” (usable 70” x 128” or 82” x 128”). Depending on window size, these smaller sizes may be more cost-effective than a full 96” x 130” sheet.
Designing with Patterns: Best Practices
Patterns on bird friendly glass present a second consideration: the pattern’s direction. Patterns fall into two categories. Non-directional patterns look the same when rotated 90°, whereas directional patterns look different when they’re rotated. A linear stripe pattern is an example of a directional pattern.
If the architect specifies a pattern with lines running two inches apart horizontally, the fabricator has to cut all glass sheets with the pattern running horizontally. Even if there’s enough glass to yield two sheets by rotating the sheet, it’s wasted because the pattern won’t run in the intended direction. On the other hand, if the architect specifies a non-directional dot pattern based on a square grid, the etched glass sheet can be rotated to yield the maximum number of sheets.
Walker Glass offers a total of eleven patterns in its AviProtek® bird friendly glass line. Of those, four are directional and seven are non-directional.
Fiscal responsibility and ecological design are important considerations in any project. It can be a challenge to balance these two factors, but intelligent preliminary planning can most certainly help. Protecting birds by choosing patterns that follow the 2″ x 4″ rule applied to surface #1 is by far the most intelligent design approach.
First, making the most of each sheet of glass by optimizing window dimensions early in the design process ensures that budgets are respected. Then, for even greater efficiency, select a multi-directional pattern for your bird friendly windows so your fabricator can rotate the glass to fit more cuts into each sheet. By keeping these design rules in mind, architects will stay within budgets and prevent bird collisions.