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<\/figure>\n<\/div>\n\n\nWhat makes windows bad (or good) at blocking noise?<\/h2>\n\n\n\n
Sound enters your home in two primary ways. One is through any air gaps you have, and the other is through glass vibration. Several factors contribute to a window\u2019s ability to block out noise: <\/p>\n\n\n\n
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- The type and thickness of glass<\/li>\n\n\n\n
- How well the window is sealed<\/li>\n\n\n\n
- The condition (and often, age) of the window frame <\/li>\n<\/ul>\n\n\n\n
Older windows often struggle with noise reduction because they have single-paned glass and deteriorated or worn seals. Over time, gaps can form around the window, allowing sound to pass through more easily. Aging frames can become warped, cracked, or damaged, which further reduces their ability to block outside noise.<\/p>\n\n\n\n
What is STC? <\/h2>\n\n\n\n
If you\u2019re researching replacement windows<\/a> specifically for window noise reduction, you\u2019ll probably see \u201cSTC.\u201d This stands for sound transmission class and refers to how well windows can block mid- to high-frequency sounds, like voices talking, barking dogs, or the TV. This is also often thought of as a good way to measure indoor noise.\u00a0<\/p>\n\n\n\n
Think of it this way: a decibel measures how loud something is; STC measures how much sound passes through something. <\/p>\n\n\n\n
NGC Testing Services, an accredited facility that does acoustic testing, notes that STC scores<\/a> range from 25 to 60+. The higher the score, the more sound reduction there is:<\/p>\n\n\n\n
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- STC 25:<\/strong> Normal conversation is easily heard and understood<\/li>\n\n\n\n
- STC 35:<\/strong> You can hear loud speech, but you can\u2019t understand it<\/li>\n\n\n\n
- STC 45: <\/strong>You can\u2019t hear loud speech, but you can hear a loud noise<\/li>\n\n\n\n
- STC 60:<\/strong> Soundproof (not possible for windows, but possible for inner walls)<\/li>\n<\/ul>\n\n\n\n
How does this translate to windows? That typically comes down to the glass:<\/p>\n\n\n\n
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- Single-paned windows<\/strong> typically have STC scores between 18 and 20<\/li>\n\n\n\n
- Double-paned windows<\/strong> often have STC scores of 25 to 28<\/li>\n\n\n\n
- Noise-reducing windows<\/strong> have STC scores of 35 or higher<\/li>\n<\/ul>\n\n\n\n
What is OITC? <\/h2>\n\n\n\n
OITC, or outdoor-indoor transmission class, is another way to think about how well a window reduces sound. Whereas STC measures mid- to high-frequency sounds often found indoors, OITC measures low-frequency sounds often found outside, like planes, traffic, and HVACs.<\/p>\n\n\n\n
Using OITC is a better, more real-world way to think about your windows. The sounds you\u2019re likely trying to block are the low-frequency sounds, especially if you live near a highway or airport in Concord<\/a>.\u00a0<\/p>\n\n\n\n
NGC Testing Services points out that a good OITC rating for windows<\/a> would be 30 or higher. They note the following: <\/p>\n\n\n\n
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- At OITC 20 to 27, you can still hear highway traffic<\/li>\n\n\n\n
- At OITC 27 to 35, you can still hear trains<\/li>\n\n\n\n
- At OITC 35 or higher, you may still hear airplanes<\/li>\n<\/ul>\n\n\n\n
OITC ratings on windows are usually lower than their STC ratings. <\/p>\n\n\n\n
STC vs OITC: What\u2019s the difference?<\/h2>\n\n\n\n
<\/div>\n\n\n\n
- Double-paned windows<\/strong> often have STC scores of 25 to 28<\/li>\n\n\n\n
- STC 35:<\/strong> You can hear loud speech, but you can\u2019t understand it<\/li>\n\n\n\n
- STC 25:<\/strong> Normal conversation is easily heard and understood<\/li>\n\n\n\n
![\"Noise-reducing](\"https:\/\/zenwindows.com\/charlotte\/wp-content\/uploads\/sites\/1031\/2026\/04\/noise-reducing-windows.jpg\")
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