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STC Ratings of Glass

Sound Transmission Class (STC) ratings indicate how well a partition or construction element mitigates sound, with laminating or double-glazing glass improving these rankings.
Published February 20, 2019

STC Ratings of GlassSound Transmission Class (STC) ratings for glass vary from poor to practically soundproof. Glass by itself is a weak noise insulator, but methods such as lamination or double-glazing can improve performance, significantly. Standard monolithic or single-pane—glass is the cheapest option, and works well for most interior applications.

What Are STC Ratings?

An STC label delineates how well a partition, such as a wall, blocks sound and reduces noise. Ratings are determined by playing a specific tone near the material and measuring the decibel value (dB) on either side. The higher the STC value, the better its insulation.

Rankings are calculated using a logarithmic formula, and can’t be combined. For example, a single ¼-inch piece of glass is 31 STC, but two ¼-inch pieces next to each other add up to 36, not 62.

 

What STC Rating Do I Need for Glass?

Before purchasing any building materials, you’ll need to decide the required level of noise cancellation. This is more complicated than just saying “35 STC is ideal for all offices,” and buying partitions to match, however.

Frameless Glass Office DoorFrameless doors such as this allow sound to leak through gaps.   (Photo Credit: Local Locksmith Riverside)

Standard construction practices typically leave gaps that enable 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. The movement of noise through the smallest cracks is called “acoustic flanking.”

 Frameless doors such as this allow sound to leak gaps.

Walls made from 50 STC-rated materials can drop into the mid-30s just by acoustic flanking. If you want to eliminate that noise, there are a number of things you can do, with glass one of the last upgrades. This includes adding a layer of drywall, filling gaps with acoustic sealant, and upgrading doors. You can also use a special ambient-noise system—called sound-masking—that plays at a specific frequency and blocks noise throughout an office. Upgraded panes of glass, called lites, are expensive, and won’t be effective unless other areas of the room are also tightly sealed.

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

Standard Glass

A single lite has an STC rating ranging from the high-20s to the mid-30s, with its score rising as the glass gets thicker. For reference, standard house walls are 33 STC, while studio-level soundproofing requires a rating of at least 45. With this in mind, a score in the mid-30s might seem low, but it’s fine for the majority of office spaces lacking all-glass construction.

Laminated Glass

Laminating glass is a popular way to increase an STC rating when cost and thermal insulation aren’t concerns. Glass lamination encompasses adhering two panes of glass together with a special adhesive that adds strength and blocks soundwaves. The adhesive—usually PolyVinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA)—hardens and keeps the two lites together, even if they crack. This is similarly utilized to make windshields and other extra-tough glass.

PVB and EVA alone are good insulators, with some laminated panes’ STC ratings reaching as high as 40 or more. The exact ranking depends on the thickness of the glass and adhesive. Special acoustic PVBs are also available to block even more noise, but they come at an additional cost.

The downside to laminated glass is the lack of insulating qualities. For interior applications this is fine, but double-glazed windows are better 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 to help with thermal efficiency in homes, but isn’t necessary for interior rooms. Sometimes, air is substituted with other gasses, such as argon, because they have better insulating properties.

The gap between lites provides acoustic insulation as well, which helps improve STC ratings. Heat efficiency usually requires a maximum gap of 16 mm, but a larger gap is always better for soundproofing. The farther soundwaves have to travel, the better.

Double-glazed glass can also provide an STC rating of up to 40, but is typically even more expensive than laminated glass, and only used for exterior applications.

Lamination and 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.

The vast majority of glass advertised as “sound-proof” consists of this combo, for maximum noise cancellation, with STCs of 45 to 50, or higher. This type of glass is likely overkill, however, unless you’re building a professional recording studio.

Single-Pane Glass Is Fine for Most Applications

If you want to make an office quieter, make sure to fill all gaps during construction, and install high-quality doors and drywall. With these improvements in place, single-pane glass is the best for the majority of interior applications.

If you need to improve a pane’s STC rating, consider lamination as a first choice, but remember this comes with an extra cost.

 


 

Dillmeier Glass Company

If you still have questions about STC Ratings, or want more detailed feedback on your project, contact us today, and we’ll help you find the perfect solution for your specific situation.

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