New city environmental standards for windows
By Grace Lovins
The Birmingham City Commission voted Monday, October 24, to adopt an amendment to the zoning ordinance that will revise the city’s window standards and adjust the definition of clear window glazing.
In November of 2019, the city’s planning board discussed the potential for an ordinance amendment that would alter window standards and directed city staff to research possible differences in visual light transmittance (VLT) figures between different manufacturers and research what VLT figures are used in other cities. In July of 2021, the commission reviewed the proposed ordinance amendment, ultimately taking no action and redirecting the planning board to clarify certain aspects of the proposed ordinance language.
The planning board voted in August of this year to recommend approval of the new ordinance proposal after adjustments were made between two discussions in May and July. Planning director Nick Dupuis noted that in addition to VLT, city staff also looked out for light reflectance back into the environment.
Dupuis continued to note that a recurring issue that has been brought up with previous developments in the city's downtown, including the phase two construction of the Baldwin Library, was the energy code. He stated that it is simpler to incorporate VLT glass into a new development where HVAC can be centered around the VLT requirement because the whole energy system works together. Retrofitting an existing building, says Dupuis, is much more difficult because it is hard to put 80 percent VLT glass because other adjustments may be needed for HVAC or insulation.
On top of the VLT requirement, Dupuis mentioned that low-E coating on windows was an additional factor that city staff looked at. Low-E coating is a microscopically thin layer of coating on a window that is transparent and reflects heat. According to Dupuis and the research conducted by the city, the best VLT that can be achieved with a low-E window coating is around 66 to 68 percent.
Mayor Therese Longe noted that the ordinance amendment, with low-E coating in mind, is the most environmentally sustainable option at this point. “This change will help all of our offices and new construction in town to have reduced energy usage going forward,” Longe said.
The commission voted 7-0 to adopt the ordinance amendment revising window standards, adjusting the definition of clear glazing and eliminating lightly tinted glazing.