Demountable Glass Walls in The Office
Glass demountable partitions have been gaining in popularity for commercial office spaces over the past decade. While the average office size has typically shrunk, utilizing demountable glass partitions gains precious inches back into usable space and creates a sense of openness. An often-overlooked benefit of glass partitions is the increased saturation of natural light deeper into the workspace. In a 2011 study The University of Oregon determined that workers that had a higher quality view from their desk and exposure to natural light took 6.5% less sick time. Cornell University also published a study that indicated an 84% drop in issues such as headaches, eye strain, and blurred vision when workers receive regular exposure to natural light. While the benefits of introducing glass partitions into the workplace are apparent, the most common grievance against the systems have been low STC ratings.
What is an STC rating?
STC is an acronym for Sound Transmission Class. For the sake of brevity, I will not bore you with the scientific definition and the mathematical formulas that are used to measure STC’s. Simply put, STC’s measure how well something attenuates airborne sound. Sound waves travel through “mediums” by vibrating the molecules in the matter; therefore, differing mediums will conduct sound waves at a higher, or lower, rate than others. Solid mediums will conduct sound at a higher rate due to their molecules being close together. Mediums such as gases conduct sound at a lower rate due to their molecules being farther apart.
When analyzing the STC performance of demountable glass wall systems, we first must look at the core components of all systems regardless of the manufacturer, aluminum extrusions, aluminum door frames, doors and hardware, and glass panels. Aluminum extrusions / door frames and glass panels are all manufactured from the same type of “mediums”. Meaning, they are all solid mediums with their molecules close together. Thus, each of these mediums will transmit sound waves at approximately the same rate. So how do we address advanced STC performance in glass wall assemblies? First, let us cut through the “smoke and mirrors” of STC performance marketing that is prevalent in the glass wall industry.
The Facts and Myths About STC’s
Many manufacturers will state that their wall assemblies carry an STC rating of 36. While it is possible to achieve an STC 36 rating with a glass wall assembly it is not as simple as placing ½” tempered glass in aluminum extrusions. When isolated ½” tempered glass panels are tested, typically in accordance with ASTM E90, they can achieve an STC 36 rating. However, when the ½” tempered glass panel is installed into a demountable wall assembly, sound paths are created. Air pockets exist within the aluminum extrusion channels. The biggest sound leak of all, as is the case with any partition, is the door assembly. As all the components come together to form the completed wall, the “assembly” STC rating will begin to drastically fall below the stated STC 36 rating of the glass panel. Yes, the glass panel alone retains its original STC rating, yet the completed wall assembly on most demountable glass wall systems will now typically test in the low to mid 20’s STC rating. So, how do we capitalize on the benefits that glass partitions offer yet provide higher STC ratings?
Achieving Target STC’s in Demountable Glass Partitions
To achieve higher STC ratings in glass wall assemblies we first must acknowledge that “off the shelf” components and poor sealing of sound paths will not satisfy the requirements. One of the first steps is to ensure that the system is designed to eliminate as many sound paths as possible. A further consideration may be the utilization of laminated acoustic glass. Laminated acoustic glass has a plastic polyvinyl butyral (“PVB”) film sandwiched in between two layers of tempered glass. The “PVB” reduces the sound waves energy (the sound waves cannot vibrate the “medium’s” molecules easily), which provides for significant noise reduction. Additionally, we must address the door assembly. Again, to achieve superior STC ratings the typical off the shelf door assemblies will not work. If superior STC performance is the goal, yet the desire is for a full glass door, then laminated acoustic glass is a must. Door frames must have full perimeter gasketing, there must be drop seals present, and all doors must have closers. Should the design require wood doors the requirements for full frame gasketing, drop seals, and closers will remain the same. As office space is at a premium, many designers are incorporating sliding door assemblies. To maintain superior STC performance with a sliding door assembly you must have full perimeter gasketing, drop seals and closers. Anything less will create unwanted sound paths, which will significantly reduce the systems STC performance.
Once the decision is made to incorporate demountable glass partitions, and a target STC range has been determined, a “best practice” would be to request independent acoustician testing of the system specified to ensure that it will perform as desired.
We at Precision Walls, Inc. would welcome the opportunity to consult with you on your next design to ensure that your fully installed system will achieve the goals you are striving to provide your client.