FIELD NOTE · SUPPLEMENTAL SET
Frit at two-inch spacing: the glazing band California wrote for birds
ISSUEDJULY 11, 2026DRAWN BY THE NIGHTLY SWEEP
An acid-etched marker in a pattern is judged, under the American Bird Conservancy's prescriptive rating, by a gloss reading taken at 60 degrees that has to come in at 6 or less, and every individual shape, whichever process put it there, has to cover at least 0.049 square inches, which is what a quarter-inch dot amounts to once somebody measures it.
None of that geometry is written for the occupant.
It is written for a constituency that will never enter the building, never lease a floor of it and never pay a cent toward it, and where the rule is enforced it is enforced as a band drawn across an elevation, in feet above grade.
The denominator is the elevation and not the glazing, and an estimator who reads it the other way prices the wrong quantity, easy enough to do because San Francisco measures the other thing.
Planning Code Sec. 139 draws a Bird Collision Zone from grade upward for 60 feet, or 60 feet up from a landscaped roof of 2 acres or larger, and requires that the zone consist of no more than 10 percent untreated glazing, which is a cap on glass rather than a share of wall.
The cap does not run citywide. Sec. 139(c)(1) reaches a building only where it stands inside an Urban Bird Refuge, meaning an open space of two acres or larger dominated by vegetation or open water, or within 300 feet of one in an unobstructed line to it, and the 10 percent is then measured on the zone facing the refuge.
Berkeley wrote no percentage at all. Municipal Code Sec. 23.304.150, added by Ordinance No. 7,864-N.S. and adopted in June 2023, reaches all transparent or reflective material from the ground to 75 feet on non-residential work, citywide and at any size. The residential gate catches only buildings with 10,000 square feet or more of floor area and an average height above 35 feet.
The conservancy's March 2025 model guidelines ask for 100 percent of glazing in a Bird Activity Zone of 0 to 100 feet above grade, and no jurisdiction on the conservancy's own ordinance list has adopted that document as written.
Four bands cross one wall at 40 feet, 60, 75 and 100 in the model, each switched on by a different trigger, and no published strike-height study stands behind any of them.
Height is not the whole scope: San Francisco treats feature-related hazards at any height, at 100 percent wherever an unbroken glazed segment reaches 24 square feet, and Berkeley regulates its High-Risk Features at any grade.
The volume is not at the towers. Loss, Will, Loss and Marra report a median 253 million a year at residences of one to three stories and a median 339 million at low-rises, against a median 508,000 at high-rises of twelve stories and up, roughly 44 percent, 56 percent and under 1 percent of the total.
Per building the order reverses: 2.1 birds a year at a house, 21.7 at a low-rise, 24.3 at a high-rise.
The 44 percent is the share no ordinance in this post touches. Berkeley's residential gate of 10,000 square feet and 35 feet of average height excludes a house before the geometry is ever discussed.
599 million MEDIAN BIRDS KILLED A YEAR BY BUILDING COLLISIONS IN THE UNITED STATES, LOSS ET AL., THE CONDOR, 2014 21.7 BIRDS A YEAR PER LOW-RISE BUILDING, THE CLASS CARRYING 56 PERCENT OF THE NATIONAL TOTAL 24.3 BIRDS A YEAR PER HIGH-RISE, AND UNDER 1 PERCENT OF THE NATIONAL TOTAL
The conservancy's rating document, updated November 17, 2025, gives the reason: subsequent monitoring indicated that 4-inch spacing might not stop the smallest birds, hummingbirds in particular, so what was once the 2x4 rule is now the 2x2 rule.
The older spacing still rates: a compliant 2 by 2 pattern earns a Threat Factor of 20 and a compliant 2 by 4 earns 25, against a threshold of 30 or less for what the conservancy calls bird friendly, the number Berkeley wrote into its ordinance as a compliance path.
Tighter is not better either. A pattern spaced closer than 2 inches also rates 25, and a lite carrying no pattern at all rates 25 where surface one is a continuous acid etch at a gloss reading of 16 or less, which is the same instrument reading the patterned marker has to hold at 6, relaxed by nearly a factor of three for giving up the pattern.
So the dot is one path and not the definition of the thing. Berkeley writes three and takes any one of them: a Threat Factor of 30 or less, the patterned glazing treatment, or an exterior screen, shutter or shading device with no gap larger than 9 inches. CALGreen's own list is prefaced shall include, but is not limited to, and it names glazing film, laminated glass with a patterned UV coating, glass block and channel glass alongside the dot, then a second family of slats, screens, netting and louvers.
Ultraviolet pattern glazing is where a specification goes soft, and the rating body says so itself: materials with ultraviolet patterns vary in effectiveness with the amount of UV light present, which varies through the day, so the pattern weakens in early morning and evening, in shade and under overcast. Songbirds see UV. Raptors and pigeons do not. Which makes UV the one path on the list whose performance nobody can confirm at the wall on the day of the walkthrough, and the one a specification should not be allowed to rest on by itself.
Which is to say the compliance path decides the coating stack, and the stack is decided in the plant well before anything is glazed. Shop drawings, glass tags and orientation at setting have to carry it, because a unit set backwards is not a punch list item.
The ordinance's word for durability is permanently, and that is the whole of the service life language in the section; its low-e definition points at the 2022 Title 24 Part 6 Reference Appendices or successor regulations, and since January 1, 2026 the successor has been the 2025 California Energy Code.
A5.107 reaches a newly constructed building, or an alteration adding or replacing 50 percent or more of the exterior glazing.
The conservancy's ordinance compilation lists eleven California jurisdictions with requirements, all of them Bay Area plus Santa Cruz. Not one Southern California jurisdiction appears on it: not Los Angeles, not San Diego, not Orange County, Riverside or Ventura.
So on Southern California facade packages the scope arrives by specification rather than by ordinance, through an owner, a green building program or the architect who wrote it into the set, and the Southern California Glass Management Association put it that way in January 2024: the standards are typically interpreted by the architectural team.
The commission that authored A5.107 filed it in an appendix the state does not enforce. Every jurisdiction that made it binding sits several hundred miles north of the work.
None of that geometry is written for the occupant.
It is written for a constituency that will never enter the building, never lease a floor of it and never pay a cent toward it, and where the rule is enforced it is enforced as a band drawn across an elevation, in feet above grade.
Ninety percent to forty feet, and sixty percent above it
The 2025 California Green Building Standards Code, Title 24 Part 11, in force since January 1, 2026, carries the provision at Section A5.107. A5.107.1 asks that no less than 90 percent of a building elevation, from grade to 40 feet or to adjacent mature tree canopy height, whichever is greater, incorporate bird-friendly mitigation, and no less than 60 percent above 40 feet.The denominator is the elevation and not the glazing, and an estimator who reads it the other way prices the wrong quantity, easy enough to do because San Francisco measures the other thing.
Planning Code Sec. 139 draws a Bird Collision Zone from grade upward for 60 feet, or 60 feet up from a landscaped roof of 2 acres or larger, and requires that the zone consist of no more than 10 percent untreated glazing, which is a cap on glass rather than a share of wall.
The cap does not run citywide. Sec. 139(c)(1) reaches a building only where it stands inside an Urban Bird Refuge, meaning an open space of two acres or larger dominated by vegetation or open water, or within 300 feet of one in an unobstructed line to it, and the 10 percent is then measured on the zone facing the refuge.
Berkeley wrote no percentage at all. Municipal Code Sec. 23.304.150, added by Ordinance No. 7,864-N.S. and adopted in June 2023, reaches all transparent or reflective material from the ground to 75 feet on non-residential work, citywide and at any size. The residential gate catches only buildings with 10,000 square feet or more of floor area and an average height above 35 feet.
The conservancy's March 2025 model guidelines ask for 100 percent of glazing in a Bird Activity Zone of 0 to 100 feet above grade, and no jurisdiction on the conservancy's own ordinance list has adopted that document as written.
Four bands cross one wall at 40 feet, 60, 75 and 100 in the model, each switched on by a different trigger, and no published strike-height study stands behind any of them.
Height is not the whole scope: San Francisco treats feature-related hazards at any height, at 100 percent wherever an unbroken glazed segment reaches 24 square feet, and Berkeley regulates its High-Risk Features at any grade.
Low-rise glass, and where the mortality actually sits
A 2014 systematic analysis of 23 studies, published in The Condor, put United States mortality from bird collisions with buildings at 365 to 988 million a year, median 599 million, second only to cats among direct human causes.The volume is not at the towers. Loss, Will, Loss and Marra report a median 253 million a year at residences of one to three stories and a median 339 million at low-rises, against a median 508,000 at high-rises of twelve stories and up, roughly 44 percent, 56 percent and under 1 percent of the total.
Per building the order reverses: 2.1 birds a year at a house, 21.7 at a low-rise, 24.3 at a high-rise.
The 44 percent is the share no ordinance in this post touches. Berkeley's residential gate of 10,000 square feet and 35 feet of average height excludes a house before the geometry is ever discussed.
599 million MEDIAN BIRDS KILLED A YEAR BY BUILDING COLLISIONS IN THE UNITED STATES, LOSS ET AL., THE CONDOR, 2014 21.7 BIRDS A YEAR PER LOW-RISE BUILDING, THE CLASS CARRYING 56 PERCENT OF THE NATIONAL TOTAL 24.3 BIRDS A YEAR PER HIGH-RISE, AND UNDER 1 PERCENT OF THE NATIONAL TOTAL
A four-inch gap, and the birds that go through it
San Francisco's qualifying geometry, as amended through Ordinance File No. 130062 effective April 27, 2013, accepts vertical elements at least 1/4 inch wide at maximum 4-inch spacing, or horizontal elements at least 1/8 inch wide at maximum 2-inch spacing. Berkeley requires 2 inches in any direction and takes either a quarter-inch dot or a line an eighth of an inch wide at that spacing, and CALGreen names 2 inches maximum horizontally and vertically and calls it the 2 X 2 Rule. The conservancy allows 2.83 inches on the diagonal.The conservancy's rating document, updated November 17, 2025, gives the reason: subsequent monitoring indicated that 4-inch spacing might not stop the smallest birds, hummingbirds in particular, so what was once the 2x4 rule is now the 2x2 rule.
The older spacing still rates: a compliant 2 by 2 pattern earns a Threat Factor of 20 and a compliant 2 by 4 earns 25, against a threshold of 30 or less for what the conservancy calls bird friendly, the number Berkeley wrote into its ordinance as a compliance path.
Tighter is not better either. A pattern spaced closer than 2 inches also rates 25, and a lite carrying no pattern at all rates 25 where surface one is a continuous acid etch at a gloss reading of 16 or less, which is the same instrument reading the patterned marker has to hold at 6, relaxed by nearly a factor of three for giving up the pattern.
So the dot is one path and not the definition of the thing. Berkeley writes three and takes any one of them: a Threat Factor of 30 or less, the patterned glazing treatment, or an exterior screen, shutter or shading device with no gap larger than 9 inches. CALGreen's own list is prefaced shall include, but is not limited to, and it names glazing film, laminated glass with a patterned UV coating, glass block and channel glass alongside the dot, then a second family of slats, screens, netting and louvers.
Ultraviolet pattern glazing is where a specification goes soft, and the rating body says so itself: materials with ultraviolet patterns vary in effectiveness with the amount of UV light present, which varies through the day, so the pattern weakens in early morning and evening, in shade and under overcast. Songbirds see UV. Raptors and pigeons do not. Which makes UV the one path on the list whose performance nobody can confirm at the wall on the day of the walkthrough, and the one a specification should not be allowed to rest on by itself.
Low-e behind the pattern, and a surface number nobody fixes in the field
Berkeley numbers the glass surfaces itself, at Sec. 23.304.150(B)(2)(c), counting from the exterior face inward. The patterned-glazing path then requires the pattern permanently incorporated into the material, on surface 1 or 2 only, exterior visible light reflectance of 15 percent or less, and, as viewed from surface 1, every low-e coating sitting behind the pattern.Which is to say the compliance path decides the coating stack, and the stack is decided in the plant well before anything is glazed. Shop drawings, glass tags and orientation at setting have to carry it, because a unit set backwards is not a punch list item.
The ordinance's word for durability is permanently, and that is the whole of the service life language in the section; its low-e definition points at the 2022 Title 24 Part 6 Reference Appendices or successor regulations, and since January 1, 2026 the successor has been the 2025 California Energy Code.
A5.107 reaches a newly constructed building, or an alteration adding or replacing 50 percent or more of the exterior glazing.
Eleven ordinances, all of them north
A5.107 sits in Appendix A5, titled Nonresidential Voluntary Measures, and the state's own 2024 CALGreen Updates handout prints it under a header reading VOLUNTARY MEASURES. The Building Standards Commission wrote the geometry and the band, and then put both where a local ordinance has to pick them up.The conservancy's ordinance compilation lists eleven California jurisdictions with requirements, all of them Bay Area plus Santa Cruz. Not one Southern California jurisdiction appears on it: not Los Angeles, not San Diego, not Orange County, Riverside or Ventura.
So on Southern California facade packages the scope arrives by specification rather than by ordinance, through an owner, a green building program or the architect who wrote it into the set, and the Southern California Glass Management Association put it that way in January 2024: the standards are typically interpreted by the architectural team.
The commission that authored A5.107 filed it in an appendix the state does not enforce. Every jurisdiction that made it binding sits several hundred miles north of the work.