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STC Rating for Windows: Keeping Sound Out of Your Home

Energy efficiency isn’t the only factor when shopping for new windows. Efficiency has a companion called noise. The “quietness” of windows is measured through something called the Sound Transmission Class (STC) rating.

While you can observe things like thickness and the number of panes when shopping for windows in person, you can’t necessarily detect the noisiness of a window just by looking at it. That’s why the STC rating is so important.

Let’s cover what you need to know to avoid noisy windows.

Why Is a Window’s STC Rating Important?

For some people, the STC rating of a window might not be that important. If you live in a quiet area overlooking meadows or farmland, you might not really care about how quiet your windows are.

However, most people don’t live among such tranquility! Here are some scenarios where homeowners may find STC ratings very important:

  • You live within earshot of a highway. This means that ever-present residual traffic noises, screeching breaks and sounds of heavy trucks shifting gears are always lurking in the background.
  • Your neighbors are close enough that you can hear them when they are playing in the yard, grilling on the patio or talking in their house.
  • You live on a main street with a good amount of traffic.
  • You live in an area with lots of sidewalk/street noise.
  • Your home is positioned in such a way that neighborhood noise tends to funnel right into your house.
  • Your property or neighborhood abuts a commercial area.

Outside noise isn’t just an “inconvenience” for most people. Things like perpetual traffic noises and ongoing chatter can drastically reduce sleep quality.

Shopping for Quiet Windows

The good news is that most new windows are very quiet. If you’re replacing outdated windows in your home, it’s going to be like night and day once you stop hearing rustling from traffic bleeding through all the time.

Even noisy chatter from neighbors is going to be pleasantly muted.

However, not all new windows offer the same level of noise reduction. Generally, something like a single-pane window with a wood frame provides the least amount of noise resistance. Touches like double-pane windows and vinyl frames tend to insulate against sound penetration.

While the frame used is important, the glass used is the key for sound defense.

However, you can’t just go by what a window is made from to know how quiet it is. This is where the STC rating comes in!

What Is the STC Rating for Windows?

Again, STC stands for Sound Transmission Class rating. This rating system was created to convey an average of how much sound is “stopped” by a window. STC ratings are also used for doors, walls and other building components.

How Is the STC Rating Determined?

STC ratings represent the average amount of noise prevented using 18 different sound frequencies. Each frequency is assigned a decibel rating.

Something important to keep in mind when reviewing STC ratings is that two numbers that are “neighbors” aren’t necessarily similar. This is owed to the nature of the logarithmic scale used to determine STC ratings.

With a logarithmic scale, every number is actually substantially higher than the number that came before it. While you don’t have to be an expert in how the STC scale works to be able to use it to make better purchasing choices when shopping for windows, it helps to be familiar with how it works. Here’s a quick breakdown of how the STC rating scale works:

  • 1. You’ll notice that STC ratings are very close in value even though they aren’t necessarily close in a “real world” way.
  • 2. While a rating increase from 28 to 30 represents a two-point increase, it’s actually showing a 90-percent noise reduction.
  • 3. For comparison, a ratings shift from 28 to 43 represents a 95-percent noise reduction.
  • 4. Ultimately, each number represents a very big amount of noise.

The bottom line is that you shouldn’t count STC noise ratings by points. It’s important to look at each rating in proportion to its place on the scale.

Yes, this is a little confusing for the average consumer who just wants to pick out some new windows without becoming an expert. That’s why shopping with help from a window expert is highly recommended.

Someone who is familiar with this scale can take options that don’t offer the level of quietness you need right off the table without the need to waste your time by looking at tons of styles that will get weeded out down the road.

What Is a Good STC Rating for Windows?

STC ratings range from 18 to 38. Average ratings vary by the type of window treatment you’re purchasing. Here’s a look at the normal STC range for common window treatments:

  • Single pane: 26 to 28
  • Dual pane: 26 to 32
  • Soundproof window with single pane: 48 to 54
  • Soundproof window with dual pane: 48 to 54

What determines the STC for single pane often comes down to the glass thickness that is used. The tightness of the fit within the frame also contributes to real-world noise performance.

Higher STC Rating Means Less Noise

For double pane, glass thickness is the big determiner of the STC rating. Double-pane windows often use a special odorless, nontoxic and clear gas in the empty space between the two glass panes. Generally, larger air space paired with thicker panes of glass will create a much better STC score.

When it comes to soundproof windows, the score often comes down to the air space. While the STC ratings are incredibly close with double and single panes on soundproof windows, it’s important to keep in mind that single-pane soundproof windows aren’t going to provide the same level of energy efficiency as double-pain windows.

If you’re looking to increase efficiency while going with a single-pane soundproof window, consider looking at low-e windows.

Is There Another Way to Compare Window Noise?

STC ratings are considered to be the only accurate comparison tools for getting true product-to-product comparisons with all other variables being equal. You’re getting a true rating of how much noise is prevented from entering your home.

Can Any Window Reduce Noise 100 Percent?

No window can eliminate 100 percent of noise. However, the difference that you’ll notice once you install windows with a good STC rating will make it seem like your home is fully silent.

Ultimately, blending a good STC rating with a high-quality window is the best way to get your home as close to soundproof as possible.