Realizing True Clarity for Exterior Façades
Clear glass is extremely common and is popular for a variety of architectural design applications, including vision glass, spandrel glass, storefronts, entryways and other exterior uses. It is often specified due to its versatility and ability to serve as a substrate for solar control, low-emissivity (low-E) coatings. In addition to its compatibility with low-E coatings, clear glass—sometimes referred to as “clear float glass, “conventional clear glass” or “standard clear glass”—is also relatively inexpensive, and is frequently selected for its neutral color.
However, when specifying glass to achieve a desired aesthetic, design professionals know that clear glass isn’t completely clear. When viewing a lite of clear glass, you may notice its slight green aesthetic, which becomes more pronounced when viewed from an angle and appears even darker at increased thicknesses or when used with low-E coatings. This can compromise design intent, especially if the goal is to create a highly transparent façade or well-lit spaces with brilliant views of the outdoors.
Iron oxide content within the glass, left over from the manufacturing process, gives clear glass its green aesthetic. Experienced design professionals are all too familiar with this undesirable attribute. However, new innovations are addressing this design challenge from both an aesthetic and budget perspective.
Low Iron and High Performance
Low-E, low-iron glass can be used for exterior applications from office buildings and institutions to luxury condominiums and mixed-use buildings.
The right glass can be the centerpiece of an amazing design concept. With its low iron content, low-iron glass significantly reduces the green aesthetic found in clear glasses, making it ideal for distinctive exterior applications where excellent clarity is required. For reference, Acuity™ low-iron glass by Vitro Architectural Glass is 60 percent less green than ordinary clear glass.
Low-iron glasses are also ideal substrates for low-E coatings, complementing the clarity improvements with outstanding energy performance. This combination allows designers to create ambitious, highly transparent, high-performance exterior façades with brilliant interior views, high visible light transmittance (VLT) and true-to-life views of the outdoors.
A low-E, low-iron insulating glass unit (IGU) typically consists of an exterior lite of low-iron glass with a low-E coating applied to the interior surface and an exterior lite of uncoated low-iron glass. This configuration can be specified for everyday applications, such as office buildings and institutions, hotels, schools, condominiums and mixed-use buildings, as well as entrances and retail storefronts. Low-E, low-iron IGUs also can be leveraged for distinctive daylighting applications such as atriums and skylights.
Fabricated glass costs are an important consideration in the façade design process. Market research indicates the installed cost of a standard glass and metal curtainwall averages $90 per square foot nationally. While the prospect of upgrading from coated clear glass to coated low-iron glass may raise budget concerns by some project stakeholders, new advances by glass manufacturers have helped bring transparent, high-performance façades within reach.
For example, upgrading a low-E-coated clear IGU to an IGU with Solarban® Acuity™ glass by Vitro Architectural Glass will typically increase the total installed curtainwall cost by only $1 to $2 per square foot. This optimization of cost, clarity and performance allows design professionals to make low-iron glass an integral focus of their façade designs.
Commercial building design is often an exercise in balance—between performance and aesthetics and budget and quality. Fortunately, options are available today that allow design professionals to avoid compromise and retain their original design intent.