Sound Transmission Ratings

Person using a lawn mower on a sunny, green grassy field with trees in the background.

Reducing outdoor noise is a concern for many homeowners in the market for replacement windows. Noise pollution affects everyone to some degree. The STC rating, or Sound Transmission Class rating, is a way to know how well a window reduces sound through absorption or by reflecting sound waves. The higher the rating, the better the window controls the sound.  For a typical single pane window you can expect a STC Rating of 18-20. Typical dual glazed windows can achieve better ratings of 25-27.

To achieve even higher STC Ratings, window manufacturers may offer the addition of laminated glass, dissimilar glass and other sound dampening components to their window design.

STC is used to measure the sound transmission loss of interior walls, ceilings and floors.  The higher the rating, the less noise penetration.

So, How Do We Measure Sound?

The unit used to measure sound is the decibel (dB). The human ear can normally detect a change in sound volume as slight as 1 dB.  Keep in mind that prolonged exposure to sound levels over 85 dB can cause serious damage to one’s hearing, and levels over 120 dB can even cause severe pain.

More about Decibels (dB)

  • Most common measure of pressure intensity or volume of sound waves

  • dBs are measured in Microbars – one millionth (1/1,000,000) of normal atmospheric pressure

  • Threshold of audibility = 0 dB

  • Change in dB level v. threshold of audibility is exponential

    • 10dB = 10 x 0dB

    • 20dB = 100 x 0dB

    • 30dB = 1,000 x 0dB, Etc.

To understand what this means in real life, here are a few examples of decibel levels for a baseline comparison:

A grandfather and young girl sitting on a park bench. The girl is whispering into the grandfather's ear, and he is smiling while holding sunglasses. The background is filled with green trees.

Whisper 15 dB

Three young men laughing and sharing stories in a bright room with large windows and exposed brick walls, one holding a notebook, another with a smartphone.

Normal Conversation 60 dB

Person using a leaf blower with blue jeans on, blowing fallen autumn leaves.

Leaf Blower 80-85 dB

Traffic jam on a city street with many cars and trucks, with traffic lights visible in the background.

City Traffic, Inside the Car 80-85 dB

Close-up of a guitar headstock with tuning pegs and part of a musician's blurred face in the background, with bokeh lights.

Nightclubs, Rock Concerts 105-110 dB

A moving train traveling on tracks during sunset, with the sun low on the horizon and a clear sky, some trees visible in the background.

Train 110 dB

A person wearing a blue work jacket and gloves is welding or assembling a metal component in a workshop.

Pneumatic Riveter 125 dB

A private jet flying above the clouds during sunset or sunrise.

Jet Engine Afterburner 180 dB

KNOW WHAT SOUND LEVELS ARE SAFE

The U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO) recommend maintaining environmental noises below 70 dBA over 24-hours (75 dBA over 8-hours) to prevent noise-induced hearing loss. The EPA also specified limits for speech interference and annoyance at 55 dBA for outdoors activities and 45 dBA for indoor activities.

Close-up of a glass mirror with a black metal corner bracket.

Benefits of Laminated Glass

  • Safety

  • Security

  • Sound Reduction

  • UV Control

  • Weather/Natural Disasters

  • Durability

  • Design Versatility

Close-up of a glass mirror with a black mounting clip and a metal frame on a white surface.

Benefits of Dissimilar Glass

  • Sound Reduction

  • Solar Energy Control

  • UV Control

  • Durability

  • Design Versatility

STC Comparison Chart

A decibel meter showing different ranges of sound levels from 18-21 to 50 decibels, with labels indicating loud, moderate, and quiet sounds.

For reference purposes only. The chart provides a range of sound transmission loss ratings that can be achieved on most types of window systems. Some window styles such as fixed and casement windows will generally perform at the upper end of the range, since they usually have a lower amount of air leakage overall. The ratings listed above are not specific to any one type of frame material. These ratings may be lower if windows are not properly installed.