In what came as a complete surprise to many in the development industry, an otherwise low-profile City of Dallas board, the Building Inspection Advisory, Examining and Appeals Board, met on July 11 to recommend approval of a number of local amendments to the City’s prospective adoption of the 2012 International Building Code, including a proposed section on "Attenuation of Solar Reflectivity Impact on Neighboring Properties."
The substantive part of this proposed amendment, the "Prescription Option", says that "all parts of the building enclosure of a structure must have a maximum exterior normal specular reflectivity of visible light of 15 percent." This would not apply to single-family or duplex structures, or buildings which do not exceed three stories or 49 feet in height. There is a second option, the "Performance Option," based on a "Reflectivity Report" done by a registered engineer, but it is unclear whether this is available for anything other than curved or "curved-in-effect" facades, for which it is mandatory, although the language says it "…will be required where alternative methods are proposed to meet the intent…" of the amendment. However, the amendment language does not explain why these are called "options," nor does it specify that either may be available.
Under current City regulations, maximum reflectivity of exterior glass appears to be unregulated, except in some planned development or special purpose districts such as the Oak Lawn Special Purpose District, also known as P. D. 193, which limits exterior glass reflectivity to 27 percent. Even that is a zoning regulation, which could be modified via certain types of zoning changes. A Building Code provision, however, is in our experience virtually impossible to vary.
This proposal is undoubtedly a reaction to the ongoing and very public dispute between a new condominium tower and one of the Arts District museums as to the alleged impact of the condominium tower's reflective glass (estimated to be 44 percent) on its Arts District neighbors. However, many view the proposed amendment as an overreaction to this one seemingly intractable, albeit very high-profile, controversy.
One potential issue with this proposal is the degree to which it might create nonconformity as to projects which are currently in the design stage. The proposal does specify that it applies "…to the construction of new and retro-fitted buildings…," so existing buildings might be exempted, but replacement of existing glass with more technologically advanced products almost certainly would be affected.
A second, but very important, issue is the consequence of this proposed amendment for the City’s explicit policy of supporting sustainability and "green building" construction methods. While the technical details of such factors as solar radiation reflectance, solar radiation absorption, and solar heat gain coefficient are far beyond the scope of this alert, the newest forms of architectural glass use reflectivity, in part, as a technique to reduce solar heating of building interiors, thus helping to reduce energy consumption.
What appears to be a rather severe restriction on glass reflectivity, with little if any apparent opportunity to vary that requirement, may well have serious unintended consequences for the City's efforts to encourage green building techniques. At the very least, this topic should be given additional time for study and broad public input from the development, architectural, and engineering communities. It is expected that the proposal will come before a City Council Committee in September and may be adopted, on the current schedule, as soon as the beginning of October.