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STC Ratings of Glass

Sound Transmission Class (STC) ratings of glass indicate how well a partition or construction element mitigates or blocks sound and reduces noise. Choosing the best material for your application is dependent upon insulation requirements, intended usage, acoustics, and other conditions.
Published May 19, 2021

STC Ratings of GlassEditor’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 vary from poor to almost soundproof. While glass alone is merely a faint noise insulator, methods such as lamination or double-glazing can significantly improve performance and noise reduction.

Decibel value (dB) levels and how much noise your application can withstand is also something to consider. For higher noise levels, it’s best to implement laminated or double-paned glass for extra protection. For areas requiring less of a barrier, standard monolithic or single-pane glass are cost-effective and work well for most interior applications.

Below we’ll outline STC rating levels, types, requirements, and suitable strategies with accompanying applications.

 

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 the dB on both sides. The higher the STC value, the better its insulation.

Rankings are then calculated using a logarithmic formula that cannot be combined. For example, a single ¼-inch piece of glass is 31 STC, but two ¼-inch pieces next to each other 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 & Factors

Similar to any design planning and processes, one of the first steps is determining factors such as sound location, room type and acoustics, dB levels, and intended usage. This is particularly important due to glass sound reduction properties, which can vary due to the wavelength encompassing the material. 

Consider the following items when determining your glass selection:

  • Which glazing type has the best noise reduction properties?

  • A thicker cut is better suited when using monolithic glass.

  • Laminated glass is best for increased thickness levels. You can also use varied thickness ranges for individual glass lites, or laminated for one or both lites.  

  • There are many insulated glass options available, such as glass thickness ranges, air spaces, gas fills, spacers, and sealants. 

  • Examine framing and sealants, which can also contribute to overall acoustics of a building’s window structure.


What STC Rating Do I Need for Glass?

It’s most prudent to decide required noise cancellation levels prior to purchasing any building materials. This requires some thought, and is more involved than simply stating: “35 STC is ideal for all offices, and partitions to match.”

Standard construction practices typically leave gaps allowing noise to 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. Noise movement through even the smallest cracks is called acoustic flanking.

Glass walls constructed from 50 STC-rated materials can drop into the mid-30s via acoustic flanking. There are several options and upgrades you can implement to eliminate this noise. This includes adding a layer of drywall, filling gaps with acoustic sealant, and upgrading doors. You can also use a special ambient noise system known as sound masking. When broadcast at a specific frequency, this works to block noise throughout an office. 

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 of the room are tightly sealed. 

While glass alone is merely a faint noise insulator, methods such as lamination or double-glazing can significantly improve performance and noise reduction.

The following are several strategies and respective applications to help improve the noise insulation of a glass partition. Keep in mind high STC panes aren’t always necessary in some instances:

Standard Glass

A single lite has an STC rating ranging from the high-20s to mid-30s, with its score increasing as glass becomes thicker. Standard walls in most homes are 33 STC, while studio-level soundproofing requires a rating of at least 45. With this in mind, a mid-30s score might seem low, but it’s suitable for office spaces lacking all-glass construction.

Laminated Glass

Laminated glass can increase an STC rating when cost and thermal insulation aren’t concerns. Lamination comprises adhering two panes of glass together with a special adhesive to add strength and block soundwaves. PolyVinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA) adhesives harden to keep the two lites together, even if cracking should occur at some point. This is similarly utilized to create windshields and other extra-strength, durable glass.

PVB and EVA alone are solid insulators, with some laminated panes’ STC ratings reaching as high as 40 or more. The exact ranking depends on the glass and its adhesive thickness. Consider special acoustic PVBs to block higher noise levels if your budget permits. 

This material is most appropriate for interior applications, but double-glazed windows are more suited for exterior walls.

Double-Glazed Glass

Double-glazed, or double-pane glass features two lites in a frame with a layer of air between them. 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 calls for 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.

Single-Pane Glass 

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 as a first choice to increase a pane’s STC rating.

 

Dillmeier Glass Company

Contact us today for questions about STC Ratings, or for additional feedback on your project. We’ll help you find the perfect solution for your specific application and needs.

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