Editor’s Note: This blog post was originally published in February 2019 and has been revised to reflect industry updates.
Sound Transmission Class (STC) ratings for glass range from low to almost soundproof. While glass alone is simply a faint noise insulator, additional fabrication processes can be implemented to improve performance and noise reduction, such as lamination, double-glazing, or a combination of the two.Decibel value (dB) levels and how much noise your glass can withstand is also a consideration. For higher noise levels, it’s best to implement laminated or double-paned glass for extra protection. Areas requiring less of a barrier can utilize standard monolithic or single-pane glass. Both are cost-effective and work well for most interior applications.
Several factors in determining the best type of glass for your project include insulation requirements, intended usage, acoustics, and other conditions.
Here is a useful outline of STC rating levels, types, requirements, and suitable strategies and applications to help you choose the perfect match.
What Are STC Ratings?
An STC label delineates how partitions and walls effectively block sound and reduce noise. Ratings are determined by broadcasting a specific auditory tone near the material, and measuring dB on both sides. The higher the STC value, the better its insulation.
Rankings are then calculated using a non-combined logarithmic formula. For example, a single 1/4-inch piece of glass is 31 STC, but two 1/4-inch pieces side by side equal 36, rather than 62 STC.
|STC Rating||Speech Levels|
|25||Normal speech easily understood|
|30||Normal speech heard but not understood|
|35||Loud speech heard and somewhat understood|
|40||Loud speech heard but not understood|
|45||Loud speech barely heard|
|50||Shouting barely heard|
|55||Shouting not heard|
Source: Quieting: A Practical Guide to Noise Control, NBS Handbook 119, National Bureau of Standards, U.S. Department of Commerce, Washington, DC, 1976.
STC Requirements & Acoustical Factors
Important factors in determining the ideal glass for your application include sound location, room type and acoustics, dB levels, and intended usage. Glass sound reduction properties vary.
Consider the following:
Which glazing type offers the best noise reduction?
Choose a thicker cut when using monolithic glass.
Laminated glass is best for increased thickness levels. This applies to individual glass lites, or laminated for one or both lites.
There are many available insulated glass options, such as thickness ranges, air spaces, gas fills, spacers, and sealants.
Examine framing and sealants, which can also contribute to overall acoustics.
What STC Rating Do I Need for Glass?
It’s prudent to determine required noise cancellation levels prior to purchasing any building materials. This involves some thought, and is more complex than simply stating: “35 STC is ideal for all offices, and partitions to match.”
Standard construction practices typically leave gaps letting noise bypass even the most insulated walls. Soundwaves follow the path of least resistance, and can travel through HVAC vents, up through ceilings and over walls, and even electrical outlets.
Glass walls comprising 50 STC-rated materials can drop into the mid-30s via acoustic flanking—even through the smallest cracks. Several options and upgrades to eliminate this noise include adding a layer of drywall, filling gaps with acoustic sealant, and upgrading doors. There’s also a special ambient system known as sound masking, designed to block noise throughout office areas.
Other options include upgraded glass panes known as lites. While these offer another alternative, they are higher in cost and aren’t effective unless other areas are tightly sealed.
The following are several strategies and respective applications to help improve the noise insulation of a glass partition. Remember: High STC panes aren’t always necessary in some instances.
While glass alone is merely a faint noise insulator, methods such as lamination or double-glazing can significantly improve performance and noise reduction.
A single lite has an STC rating ranging from high-20s to mid-30s, with its score increasing as glass thickens. Standard walls in most homes are 33 STC, while studio-level soundproofing requires a rating of at least 45. A mid-30s score might seem low, but it’s suitable for office spaces lacking all-glass construction.
Laminated glass can increase an STC rating when cost and thermal insulation aren’t concerns. Created by sandwiching various interlayers in between two glass lites, this special adhesive adds strength and blocks soundwaves. Laminated glass will also stay in place, even if a significant impact should occur. This is similarly utilized to create windshields and other extra-strength, durable glass.
With some laminated panes’ STC ratings reaching as high as 40 or more, the exact ranking depends on the glass and adhesive thickness.
Double-glazed, or double-pane glass features two lites in a frame with a layer of air in between. This setup is often used for thermal efficiency in homes, but isn’t necessary for interior rooms. Due to its higher insulating properties, other gasses such as argon are sometimes substituted for air.
The gap between lites also provides acoustic insulation to improve STC ratings. Heat efficiency usually requires a maximum gap of 16 millimeters, but a larger space is always better for soundproofing.
Double-glazed glass can also provide an STC rating of up to 40. Costing more than other materials, this is used mainly for exterior applications.
Laminated & Double-Glaze Combinations
Laminated and double-glazed glass both hold STC ratings of 40, but anything higher typically requires a combination of the two. Maximum noise insulation is achieved by laminating one or more lites in a double-pane piece.
Most glass advertised as soundproof consists of this combination for maximum noise cancellation, with STCs of 45 to 50, or higher. This glass type isn’t necessary unless your application requires the highest soundproofing levels, such as a professional recording studio.
To achieve quieter office areas, ensure all gaps are filled out during construction, and install high-quality doors and drywall. With these improvements, single-pane glass is the best for the majority of interior applications.
If your budget permits, consider lamination a first choice to increase a pane’s STC rating.
Which Glass Is Best for Soundproofing?
Choosing the best glass type for soundproofing is dependent on several factors—all of which should be considered during project planning. While laminated, double-glazed, and other combinations are suitable choices, the decision is based on room type, acoustics, application, area of use, and more.
Contact Dillmeier Glass Company for questions about STC ratings. We’ll help you find the perfect solution for your project!