STC Ratings for Windows: Best Windows for Sound Reduction
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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.
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.
Single Pane Glass
Double Pane Glass
Impact Windows (PVB)
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.
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.
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.
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.
Windows which have single pane glass are the most problematic when it comes to noise transmission, since, obviously, they only have one layer of glass to keep the noise out.
Their STC range is usually 26-28, which is really low. This means that you can clearly hear what the person standing near the outside window is saying if they're speaking in a normal tone, and they can hear you as well.
Also, heat travels easily and rapidly through these windows, which makes your house too hot in the summer and too cold in the winter, so that’s another problem that insulation can solve.
These windows are without a doubt the cheapest ones and they are easy to install, but, ironically, you will probably end up spending a lot of money on heating because of the cold air that passes through them and you’ll have to put up with noise.
The best solution in this situation would be to double glaze the windows. This means that you have to install an additional layer of glass.
The most common type of double glazed windows is casement windows.
The prices for this kind of window can vary from $200 to $2000, depending on the material and size.
If you use laminated glass, then the STC rating will go up to 35 or more, which is definitely an improvement.
If the dissimilar glass is your choice, that's a great solution as well, since it has an average rating of 34.
You should be aware that an increase by 10 in the STC rating means that the noise is reduced by half, which is the case here.
Still, there are some disadvantages to this solution that you have to consider before making your choice.
If you use laminated glass, then the windows will not be as ecological as they would be if you used Low Emission glass. Also, although this option is really effective, it is by far the most expensive one.
I should also let you know that while double glazed windows can do an amazing job at keeping your house warm, they can also make your room temperature too high in the summertime, which is not a problem that can be easily overlooked.
Let me tell you a bit more about the dissimilar glass.
Dissimilar glass windows have two glass panes that are not equal in thickness, which is why it’s named the way it is.
You must be wondering why and how this works.
Well, one pane ensures that none of the lower frequency sounds enter or leave the room. Pane number two blocks higher frequency sounds.
This way you can achieve more control over the noise and greatly improve the STC rating of soundproof windows in comparison to regular double pane windows.
Single Hung Windows
Single hung windows also known as sash windows have a moving sash that slides from the bottom part of the window to the top. The top part doesn't move and remains fixed into the frame.
They are usually quite similar to one pane windows and are not the most popular way to reduce sound transmission.
Double Hung Windows
Double hung windows also known as double sash windows have two moving sashes. You can slide them up and down.
While they provide good ventilation they are not my first choice when it comes to sound abatement.
A storm window is nothing but an extra window most commonly used outside the original window.
This is a cheap alternative and is not the best solution for sound control windows.
Your best bet would be to install soundproof windows if you want to get the best possible sound reduction results.
Even though vinyl windows have a substantial share in the window market (around 70%) they are not the ideal solution for soundproofing.
A window unit made from vinyl has low mass compared to other types of windows.
You would need a thicker than the usual window to work well for sound abatement.
They are, however, very energy efficient due to their multi-layered pockets that effectively slow down the transfer of heat.
They may get pricey but aluminum windows sure get the job done when it comes to sound control.
Having the highest metrics in reducing coefficients, aluminum windows will help with severe noise problems like no other.
The design of aluminum windows is usually minimalistic and less bulky compared to other materials so you won't have to deal with difficult installations.
They are easy to customize in terms of color options and you can also choose the ones that are made from environmentally-friendly materials.
Due to their build windows made from aluminum will not disfigure with drastic temperature changes and are generally more durable than other types of windows.
Because they are quite sturdy they can bear greater loads with thicker glass. This makes them great at reducing sound frequencies up to 50 decibels.
You already know that laminated glass is a great material for noise prevention. But why exactly?
I can show you through an example of a certain type of windows called ‘’impact windows’’ which consist of two layers of laminated glass and an inner layer of PVB between the laminated layers.
People don't usually install these windows with sound insulation in mind but in order to protect themselves from natural disasters and dangers.
And yet, impact windows have a really high STC rating, especially because of PVB.
PVB stands for Polyvinyl Butyral, which is a plastic material that is often used for making safety windows of all kinds.
PVB does not have the same density as glass. While the glass reduces the sound that travels in and out of the room, PVB breaks up the sound, which is even more effective.
This is why laminated glass windows are so good at sound reduction.
An impact window has a rating of 32-35, which is a really significant advancement since that means that the noise has been reduced by half.
How To Improve STC Ratings For Windows
No matter how well-designed they might be, double- and triple-paned windows can always be helped along to eliminate energy loss. Here are tips to help improve the efficiency of your windows:
- Use thermal curtains: Thick thermal curtains drawn across the windows at night significantly raise the window's overall R-value.
- Add window insulating film: You can apply your own thin clear layer of plastic film to the window trim with adhesive. Application of heat from a hairdryer will tighten the film.
- Weatherproofing: Older windows may have hairline cracks or they are beginning to open up around the framing. Those problems let cold air enter the home. Using an exterior-grade silicone caulk can close up these leaks.
- Replace foggy windows: Windows that are foggy between the two panes of glass have lost their seals and the gas has leaked out. It is usually best to replace the entire window to regain the energy efficiency in your room.
Conclusion: STC Ratings for Windows
Finally, now that I’ve introduced you to STC and different types of window insulation, it is my hope that you will manage to find the best possible option for your home and finally get rid of unwanted noise.
Laminated glass is my personal favorite for noise reduction, regardless of its price.
It has the highest STC rating compared to all other types of glass, which is why it can be a great investment on your part to make it your choice for sound reduction.
Whether you’ll choose to double glaze your windows use triple pane glass, or to use dissimilar or laminated glass is up to you.
As you’ve had the chance to see, each option has its advantages and disadvantages, and they all have different STC ratings, you just have to pick an option that is the most appropriate for you and your home.
You might also like: How to Determine the STC Rating of a Wall