STC Ratings for Windows: Best Windows for Sound Reduction

If you live in a busy area with plenty of traffic passing by, or next to a pedestrian street that is always filled with people, you’re probably not too thrilled that you have to put up with all of that noise.

Perhaps you’re woken up every single morning by the annoying sound of your neighbor mowing the lawn really loudly when you just want to get some sleep, or you live next to a construction site or a playground.

Whatever your problem may be, I am probably right in guessing that the idea of soundproofing your living space has crossed your mind at least once.

Even if you have no previous experience with soundproofing or noise reduction, you have no reason to worry, I am here to help you and guide you through the entire process.

First of all, I have to introduce some basic terms to you about sound control.

I won’t bother you with too many facts and explanations about sound transmission or sound waves theory, I just want you to get a basic idea of how soundproofing works so that you can solve your problem more effectively.

STC Ratings

So, unless you’re familiar with sound reduction, you probably haven’t heard of STC until now. STC stands for Sound Transmission Class and refers to how much sound is being stopped by a surface or a specific material.

It might sound a bit confusing, but it is actually quite simple - STC ratings are used to determine how many different types of materials can reduce sound waves coming from different sound frequencies.

Obviously, the higher the rating is, the more sound is blocked by this material.

No matter what you’re planning to block sound transmission, it is always very useful to know at least the approximate STC rating for different kinds of materials before you decide on the type of material you will use.

Noise can be transmitted in and out of your room in many different ways. As you may already know, the noise mainly spreads through thin walls, hollow doors and through windows.

There are many ways to securely and successfully soundproof both walls and doors by relying on STC ratings for materials that you’ll use.

However, in this article, our main focus will be window soundproofing, since most of the noise travels through the windows.

STC ratings for sound control windows largely depend on the glass type.

The average STC rating for a regular single pane window is 27.

Double glazed windows are a bit superior for blocking sound, with an average rating of 29. If thicker glass material is used, the rating can go up to 35.

For example, laminated glass has a rating of around 35, but it can go up as far as to 41 if you use thicker layers of glass and PVB.

Your glass dimensions should be as large as possible, and the dimensions of the window frame as small as possible for best sound control.

Air Space

An important consideration when opting for windows with multiple panes is the air space between the panels.

In essence, the larger the air space between the panes of glass the more sound the window can block.

Shoot for an air gap anywhere from 40mm to 140 mm for best possible results.

How Materials Affect STC Ratings

There are a multitude of window types that absorb sound differently, depending on materials they're made from, the type of glass, glass thickness and the frame.

I will try to cover most of them for you so that you can easily find the exact solution appropriate for the window type you have at home.

First of all, I have to introduce you to typical materials that window frames can be made of, including wood, vinyl, fiberglass, etc.

The material that the frame consists of can affect the STC rating quite a bit.

You can choose the option that seems the most appropriate for your situation and amount of unwanted noise.

Wood windows are a reasonable option, they don’t spoil the look of the house and are quite affordable.

However, water largely affects and damages wood over time, so you should consider that before picking this frame type.

Vinyl frames are good at insulating, but their weakness is that they are very sensitive to temperature changes, so they are not ideal for noise reduction in the long term.

Fiberglass is a material of high quality and it can stay intact for a long time, but not everyone can afford to use it.

Now you know what the best material the frame should be, but what about the glass on the windows?

Regular glass doesn’t really offer a strong protection from unwanted outside noise.

However, as I’ve mentioned already, laminated glass is a different story entirely.

It is manufactured for the sole purpose to reduce noise. Though it may be expensive, it is the most secure option and you won’t be disappointed if you opt for it.

Glazing the windows

Glazing is a process of adding another layer or multiple layers of glass to the window in order to absorb noise better. 

Window glazing is the glass inside of a window, which can be single, double, or triple glaze (also known as single pane, double pane, or triple pane).

Double Glazed Windows

Double pane windows have two glass panes bonded together by a spacer and separated by a gap between 6mm to 20mm.

The gap is hermetically sealed and filled with argon to provide an added insulation layer. Ideally, double glazed windows and doors should use toned or low-E glass to improve their performance.

Structurally, the gap between the separated panes in dual glazing window types is the critical difference between double-glazed and single-glazed windows as well as doors. Yet, the real difference lies in the unique benefits of double glazing.

Three-Paned windows

Triple pane windows may look good on paper but that third pane does not always improve the window's ability to fix the problem of noise penetration.

Keep in mind that if you add more layers of glass, that doesn’t necessarily have to mean that the STC rating will be higher, because there are many other factors that have to be taken into consideration when soundproofing the windows.

For example, there is a common misconception that the insulation will be more effective if you add three layers of glass.

Some triple pane windows feature mixed glass thicknesses for each pane which can lower the vibrations between them. This can potentially help with reducing low frequency sounds.

But what most people don’t pay attention to is the importance of air spaces that exist between glass layers.

A window with three glass layers can often have tighter spaces between the layers.

Since the spaces are smaller than usual, they can actually cause the sound to amplify, which creates an additional and possibly bigger problem than before.

In most cases you would be better off choosing fixed windows with laminated glass panes which reduce noise quite well.