Architects, designers and project managers specifying products for building façades face an ever-growing range of glass products. The design team has many ways to express creativity and innovative options to achieve energy goals. Every decision affects how the building looks and performs. With all the options available, how do you know which glass products are right for your project?
Guardian SunGuard AG 50 coated glass and SunGuard SuperNeutral 68 coated glass on OATI. Photo: Mitchell Stier
Let’s examine key considerations in specifying glass.
Pushing Performance
There are multiple measurements to look for when you are selecting glass to meet performance goals:
- U-Factor measures heat gain or loss through glass due to difference between indoor and outdoor temperatures. A lower number means better performance. There are recommended U-factors for each climate.
- Solar Heat Gain Coefficient (SHGC) measures how well a product blocks heat caused by sunlight. It’s measured in values from 0 to 1. The lower the SHGC, the less solar heat it transmits, and the more comfortable occupants are. The right SHGC can help preserve warm interior air in cold climates and help retain expensive air-conditioned air in hot climates. Specify 0.4 or below in the North, and 0.25 or below in the South.
- Visible Light Transmission (VLT) is the percent of visible light that passes through glass. The most visible light you can get from low-E product is about 78%. VLT can help facilitate daylighting and, if designed thoughtfully, can aid in offsetting electric lighting and cooling loads. A higher VLT can enhance daylighting, and a lower one can add more privacy. Managing VLT will help avoid glare.
- Light to Solar Heat Gain Ratio (LSG) compares the VLT to the SHGC. A 2:1 LSG ratio can be achieved with low-E coatings. A higher LSG ratio can make rooms brighter and create more open views.
Low-E glass façades can maximize natural light with minimal impact on solar heat gain for those façades that have long-term sun exposure. Different coatings can impact glare and solar heat gain in different ways.
Building orientation plays a tremendous role in energy performance and occupant productivity. Solar heat gain and daylighting can vary greatly depending on the path of the sun in the summer vs. winter. Overlooking these elements can result in excessive heat gain or glare issues that may compromise energy performance and occupant comfort. The sun’s arc will impact each façade differently:
- North: All-day indirect sunlight
- South: Solar exposure throughout the day
- East: Direct light at low angles during morning hours
- West: Direct light at low angles during the afternoon hours
Low-E glass façades can maximize natural light with minimal impact on solar heat gain for those façades that have long-term sun exposure. Different coatings can impact glare and solar heat gain in different ways.
Seeing Samples
Glass samples can help you visualize final glass appearance. Tips for evaluating samples:
- The best way to view samples is outdoors on an overcast day.
- View triple silver low-E coatings at a 40- or 50-degree angle to ensure desired color.
- View with control sample to further compare color.
- Never hold a sample right in front of your face; it won’t show color accurately. Hold it about 10 feet away.
- Turn a sample over to see the reflectivity of the glass, as well as the interior reflected aesthetic. This is a valuable consideration for hotels and multifamily buildings where nighttime views are important.
- Visit the job site in different lighting conditions and times of day to get the best idea of how lighting will impact the glass.
Glass samples come with two backgrounds:
- A black background behind your glass sample will replicate a punched open window application without lighting turned on.
- The white background represents transmitted color, or what you see looking through the glass. A white background behind your glass sample will demonstrate a nighttime application, an application where there is a white shade behind the glass or a situation where a user is looking through an all-glass, corner elevation.
A certain spandrel color or a shade behind the glass can make a difference in the reflected and transmitted color of the glass. The decision to build cubicle walls or create open interiors can affect the way glass looks from the outside. Consider all of these factors (and more) before specifying.
Do Digital
There are many online resources to help simplify the process and guide you through specifying glass. For example, Guardian Glass has developed Glass Analytics, easy-to-use, advanced software for glass and glazing system analysis. These online tools offer a comprehensive suite of engineering and analytical reports that demonstrate the advantages of high-performance glass in building façades.
Talk to your manufacturer early so that the team of design and technical advisors can forecast your needs—they can be your glass resource as you plan your project. Equipped with a plan and resources for your glass selection, you can surpass your project goals.
Darijo Babic is the director of architectural sales and is responsible for increasing Auburn Hills, Mich.-based Guardian Glass specifications and sales for commercial projects by leading and directing inside and outside sales teams. For more information, visit www.guardianglass.com.