Many homeowners have to tolerate road traffic noise on a daily basis. We experienced this ourselves. We lived about 60 feet from a busy road and it was just impossible to get a good night’s rest at times. We had a new born son at that time, and many parents will know how crucial it is during this highly exhausting period to have a conducive environment for sleep. We were desperate to soundproof our bedroom from the traffic noises. We pored over the internet hoping to find solutions and tried many DIY soundproofing tips.
To our disappointment, these methods did little to help. We realized we needed real soundproof windows. Information on the Internet were inconsistent and insufficient. We needed more convincing to justify the high investment we were making.
Thus began our journey to learn how to choose the best soundproof windows for noise reduction. We read scientific journals, borrowed architectural acoustic textbooks and conducted our own experiments.
This guide you are reading now is the culmination of almost 80 hours of research and study (you won’t believe how much science there is to learn about this). We assure you there will be no product sales pitch. There is real data from scientific studies and our own experiments. We will tell you exactly what type of windows to choose to get the best soundproofing results. You will save money by avoiding costly mistakes and get the maximum results.
For those in a hurry, these are the pertinent findings from our research on the best soundproof windows
- Double glazed windows have superior results to single glazed windows
- Triple glazed windows have marginally better results than double glazed windows if the air gap is kept constant, but cost much higher
- For double glazed windows, use of differing glass thickness leads to better soundproofing than using 2 glass panes with the same thickness
- For double glazed windows, 50mm is the minimum air gap distance you need to achieve good soundproofing against traffic noises
- Thicker glass is better – as long as air gap distance is not compromised
- Normal air is as good as Argon for the air gap
- PVC window frames have marginally better soundproofing than aluminum window frames
- Hinged windows have better soundproofing than sliding windows
Hearing Loss Risk Assessment
Before we begin, you may want to take 3 mins to do a short risk assessment to see if you are at risk of developing noise-induced hearing loss.
This is a simple screening test to determine your risk level of developing noise-induced hearing loss. It is developed based on your exposure to excessive loud noises and your attitude towards ear protection.
*Note: This is not a diagnostic test for hearing disorders. If you feel that you may have a hearing disorders, you should seek professional medical attention immediately.
Some Terminology To Get You Started
Soundproofing is done to block sound from entering or leaving a room. This is usually accomplished with the use of hard and heavy materials. The high density of such materials is needed to reflect sound.
This is an alternative term for soundproofing. Sound-insulating materials stop sound waves from traveling to or from a room.
On the other hand, sound absorption products absorb echoes within a room. Materials can be applied to walls or ceilings to “soak up” the sound waves as they hit the surface, thus preventing sound from bouncing around the room. Such materials are usually soft or porous.
How Is Sound Measured?
Sound is a vibration that travels through air, liquid or solid. Scientists describe the most important features of sound through a sound wave. This is a repeating pattern of high pressure and low pressure regions moving through a medium. The most important characteristics to note are wavelength, amplitude and the number of wavelengths per second (frequency).
When the sound wave reaches the human ear, it makes the tympanic membrane vibrate. This vibration sends a signal to our brain, which processes the information as sound.
Frequency refers to the speed of the sound’s vibration. The unit of measurement is Hertz (Hz).
- 1 Hz = 1 sound wave per second
- 20 Hz = 20 sound waves per second
- 20,000 Hz = 20,000 sound waves per second
Humans typically can hear sounds with frequencies ranging 20 – 20,000 Hz. This range may shrink as we get older, due to physiologic or pathologic hearing loss. Examples of low frequency sounds (also known to be of low pitch) include a double bass or a man’s deep voice. High frequency sounds (known to be of high pitch) include the sounds from a flute or violin. Watch and listen to the video below to see how good your hearing is!
Amplitude measures how forceful the sound wave is. This is measured in logarithmic decibel (dB) units. The term “logarithmic” just means that numbers on the scale are not the same distance apart. The decibel scale caters to human audibility.
- Near total silence equates to 0 dB
- A sound 10 times more powerful than that is 10 dB
- A sound 100 times more powerful than near total silence is 20 dB (not 100 dB!)
- A sound 1000 times more powerful than near total silence is 30 dB
- … and so on…
How is Sound Reduction Measured?
Transmission loss refers to the change in dB across the wall or window.
Sound Transmission Class (STC)
STC is frequently used by manufacturers to report the sound-reducing capabilities of their products. The STC of a tested product is calculated by plotting on a graph the Transmission Loss values tested at 16 standard frequencies (125 Hz – 4,000 Hz). The resultant graph is compared against standard STC reference curves. The STC rating is determined by selecting the closest match between the test (in green) and reference curves (in pink).
A higher STC rating implies better soundproofing.
|STC Rating||Subjective Experience|
|25||Normal speech can be easily heard and understood|
|30||Loud speech can be easily heard and understood|
|35||Loud speech heard but no understood|
|40||Loud speech now only a murmur|
|45||Loud speech not heard, heavy traffic noise still a problem|
|50||Very loud sounds such as a stereo can be faintly heard|
However… The STC reference curves only incorporate testing of sounds with frequencies between 125 Hz to 4,000 Hz. Thus, STC ratings do not apply to situations where sound frequency is lower than 125 Hz or higher than 4,000 Hz. Unfortunately, noise complaints are most commonly due to low frequency noises such as that from traffic, airplanes, bass instruments and industrial equipment. You can also see from the graph below that between 100 Hz to 125 Hz, transmission loss has a significant dip.
Outdoor-Indoor Transmission Class (OITC)
The OITC rating system is similar to STC, but it measures transmission loss between 80 Hz to 4,000 Hz. Because it is applicable to a lower frequency, it is actually a more relevant rating than STC when evaluating traffic noises. Higher OITC ratings indicate better soundproofing.
Most exterior noises are low frequency noises, and these can travel further than high frequency sounds. This is why you can hear a heavy vehicle from a distance, but may not hear a higher pitch violin being played at the same distance away. OITC is relevant to exterior walls and windows where low frequency performance is important, while STC is more suitably used indoors.
Unfortunately, OITC is a much newer rating system than STC and hence has not received as much attention as STC. Thus, the data on OITC is not as robust, and is seen less frequently in this guide.
Road Traffic Noise
Transportation noise remains the main source of environmental noise pollution. This includes road traffic (more about that later), rail traffic and air traffic. Railway noise varies depending on speed of the train, type of engine, roughness of wheels and rails. At train stations, additional noise is generated by signaling processes (whistles, loudspeakers) and the revving of engines. Closer to tunnels, ground conditions can generate additional vibration. High-speed trains, while more friendly to the environment in terms of emissions, produce higher-frequency sounds similar to an aircraft.
Aircrafts have been a boon to international / domestic travel, but are a bane to communities in the vicinity. Take-offs and landings are notorious for producing intense noise. In general, larger and heavier aircrafts produce more noise. This also seems to be the trend, with airlines aiming for maximal passenger and/or cargo capacity, in order to improve profit per flight.
However, for most residential areas, the most common source of transportation noise comes from road traffic.
The video below captures the road traffic conditions on a typical day in Bombay, India. The highest recorded sound was 105 dB. Try to sit through that while working or resting.
For a rough idea of how bad traffic noise can be, we look at this project report published for the Transport Research Foundation . Audio monitors were set up along the side of a busy road and the sound readings from vehicles that passed by were recorded. Here are the results.
|Category||Types of Vehicles||Sound Range|
|Light||Motorcycles, cars, vans||70 – 86 dB|
|Medium||Medium goods vehicles, buses, coaches||74 – 92 dB|
|Heavy||Heavy vehicles||74 – 90 dB|
For reference, loudness of a gas-powered leaf blower or a hairdryer ranges between 90 – 100 dB. So, you can imagine how loud these vehicles can get. In addition, the majority of vehicles subjectively classified as noisy had increased low frequency noise (between 63 – 125 Hz).
The level of traffic noise also depends on a few other factors
- Volume of traffic. The higher the volume, the louder the noise
- Speed of traffic. The faster it is, the louder the noise
- Number of trucks in the traffic flow. The more trucks, the louder the noise
- Distance between the noise source and the receiver. With increased distance, there is less noise
- Presence of natural/man made obstacles which may block the sound wave
There are numerous studies that have proven the health effects of noise pollution on humans. Examples of these effects are hearing loss, tinnitus, cardiovascular diseases, behavioral problems and sleep disturbances.
How To Soundproof My Windows
For those homeowners affected by traffic noise and wants to know how to stop road noise, this is where it starts to get interesting. This section will cover the DIY methods while the next section will be on soundproof windows.
DIY Soundproofing Methods: Do They Help?
Common DIY methods recommended by websites and blogs to soundproof your home include:
- Sealing windows gaps with caulk
- Rearrange furniture
- Soundproof / sound absorbing curtains
- Window plug
- Install thick shades
- Attach a layer of acrylic or glass over the inside of the window
- Soundproof window inserts
- Window soundproofing film
- Cover the window with acoustic panels
- Block your window with barriers like vegetation
We tried to look for objective data on the effectiveness of these methods but unfortunately most were reviews from other bloggers or product companies trying to sell these products. We took these reviews with a big pinch of salt because they were mostly personal experience or stories with no objective data to back up their claims.
There were, thankfully, 2 studies that looked at soundproof curtains and 1 study that looked at vegetation barriers. Here are the results…
Also known as soundproof curtains, these are heavy curtains that are tightly woven and go from the ceiling to floor. They need to be several inches past each side of the window. The principle behind their application is they need to cover as much area as possible around the window to achieve a seal around the sides (if that is possible). Because of their design, they also have applications in thermal insulation and light blocking.
In both studies [2,3], acoustic curtains were found to reduce noise from 22 dB to 25 dB. However, these were industrial grade fabric curtains with sound absorbing material specifically built in to reduce industrial noises. Also, in order to achieve a reduction of 25 dB, they had to use 2 layers of curtains to increase the thickness of the sound barrier.
25 dB reduction is pretty decent. If your traffic noises are capping at about 55 dB, this might be a good option to bring your house noise level down to 30 dB which is a very comfortable level for rest and relaxation.
However, access to industrial grade soundproof curtains and their installation can be extremely difficult. They are heavy, cumbersome and you need more than 1 layer! Did i mention they look really awful as well?
Watch this informative video below which explains how to maximize the effectiveness of acoustic curtains.
The other study  looked at using vegetation as a barrier to reduce noise transmission. The results were pretty dismal. They found that a thin layer of vegetation (20cm to 30cm) reduced the sound transmission by only 1 dB.
We decided to give it a go.
This is our balcony. We live about 60 ft from a busy road. It may not look busy now but this is at 11am in the morning where the peak traffic has passed. Despite that, we still got an average noise reading of about 68 dB and the highest recorded was 73 dB when a motorcycle zoomed by.
I closed my windows and the noise levels reduced to 58 dB.
Enter the weatherstrips. It got a little difficult to lock the windows due to the additional layer.
With this addition, noise levels dropped from 58 dB to 52 dB. It did reduce the noise but 6 dB is hardly a game changer when you are dealing with heavy traffic noises.
|Windows Open||Windows Shut||Windows Shut with Weatherstripping|
|Noise Level||68 dB||58 dB||52 dB|
These results suggest that DIY soundproofing methods have pretty limited use in reducing noise levels. These methods are usually quite affordable and may be a reasonable option for a temporary measure (e.g. rental apartment). However, if you are looking for a permanent solution, you are probably better off with getting soundproof windows.
Key Takeaway: DIY soundproofing methods can work if your noise problem is mild (below 55 dB)
How To Choose The Best Soundproof Windows
Type Of Glass
There are 3 types of glass that might be used in the windows that you see in your homes.
Float Glass / Annealed Glass
This is the most widely used glass in our homes. It allows for maximal light and heat penetration and is used whenever there are no specific glass requirements. The STC of float glass is in the high 20s to low 30s. The cost is also the lowest at about $3 per square foot.
Tempered Glass / Toughened Glass
This is a type of safety glass that is processed by thermal or chemical treatment to improve its strength and physical properties. Due to its increased strength, it can be used in a range of demanding applications. This includes vehicle windows, shower screens, glass tables, mobile phone screen protectors and as a part of bulletproof glass. The STC rating of tempered glass is in the high 20s to low 30s (similar to float glass) and it is not commonly used in soundproofing solutions. The cost of tempered glass is about $12 – $14 per square foot.
Laminated Glass / Acoustic Grade Glass
A laminated glass contains 2 pieces of glass that is held together by an interlayer (you may think of this as the glue that holds the 2 pieces of glass together). This interlayer is typically applied with polyvinyl butyral (PVB).
One of the most common uses of laminated glass is in soundproofing and this is due to the interlayer of PVB that produces a vibration damping effect. Because of its soundproofing properties, it is sometimes referred to as acoustic grade glass. The STC rating of laminated glass is in the mid 30s. The cost of laminated glass is about $10 – $20 per square foot.
|Properties||Application||Average STC Rating||Cost per Sq Foot|
|Float Glass||Can be shaped easily||Anywhere without specific glass requirements||High 20s to low 30s||$3|
|Tempered Glass||Good mechanical strength||Vehicle windows, shower screen, glass tables||High 20s to low 30s||$12 – $14|
|Laminated Glass||Good sound insulation||Vehicle windshield, soundproof windows||Mid 30s to high 30s||$10 – $20|
Key takeaway: Your soundproof window must have some form of laminated glass to have a good outcome
Glazing is used to describe the number of glass panes in a single integrated window unit. For example, a double-glazed (or double-paned) window refers to a window that has 2 glass panes while a triple-glazed (or tripe-paned) window would refer to a window with 3 glass panes.
NOTE: This is not to be confused with secondary glazing which refers to installing an independent internal window to your existing window on the interior side of the house. In doing so, you are creating a double glazing system on your own by combining two single glazed windows. This can sometimes be referred to as retrofitting.
Double glazing and triple glazing are used by soundproofing window makers to improve the soundproofing capabilities of windows. The concept of glazing is based on 2 principles;
- Overall glass thickness is increased with more layers
- Air between the glass layers provides insulation
Double and triple glazing come at a premium compared to single glazing. The estimated cost for a double-glazed window is about $50 to $80 per square foot and about $80 to $150 per square foot for a triple-glazed window. And the all important question…
Are double-glazed and triple-glazed windows worth their increased cost?
Yes and No.
Numerous studies [5,6,7] have shown that double glazing and triple glazing outperform single glazing for sound reduction purposes. BUT, that is only true if certain conditions are met. The most important criteria for improving the soundproofing quality in glazing is actually the layer of air in between the glass and not the number of layers of glass you have. Pilkington’s study demonstrated that double glazing does not reduce sound transmission much more than single glazing if the air layer is not thick enough. Which brings us naturally to the next question…
Cost Of Double Glazing Windows And Triple Glazing Windows
|Glazing||Cost Per Sq. Ft.||Estimated cost for a window 4 ft. by 5 ft. (20 sq. ft.)|
|Single Glazed||$10 – $20||$200 – $400|
|Double Glazed||$50 – $80||$1000 – $1600|
|Triple Glazed||$80 – $150||$1600 – $3000|
How thick is thick enough?
There are 2 studies [5,6] that answered this for us. It was found that double glazing is superior to single glazing only if the air space is close to or greater than 50mm. Also, once the air gap goes beyond 200mm, acoustic improvement is no longer worth the trouble as the increment is negligible.
For homeowners troubled by traffic noises, consider increasing this air gap to 100mm. An air gap beyond 100mm provides better soundproofing for low frequency noises which is the characteristic of most traffic noises.
We interviewed Ted White, President of Soundproofing Company Inc, and he echoed our findings. “You need a larger gap to get any benefit from separation between panels. In truth, for anything meaningful, you’d need 150mm gap between huge mass and you can’t build a window with such huge space between the panes. So windows always lack in the low frequencies, compared to the walls the windows are mounted in.”
What if we go 1 step further and triple glaze our windows? Will that reduce the need for such a large air gap? Unfortunately no. As mentioned, the air gap is more important than the number of layers of glass. Mateus’s study  compared double-glazed and triple-glazed windows of similar size and air gap. His results showed that triple glazing only improved the sound reduction by 2 dB. That is not even discernible by the human ear!
In cases where your window space is fixed / limited, choosing a triple-glazed window over a double glazed window compromises on the air gap, because space is taken up by the additional glass pane. the result is poorer sound insulation especially for the low frequency noises (traffic noises). In such scenarios, you would have wasted your hard earned money to get poorer results.
(L) – Laminated
(12) – 12mm of air and etc for other values
|Noise reduction at 100 Hz |
|Noise reduction at 1000 Hz |
|Noise reduction at 5000 Hz |
|4mm – (12) – 4mm||23 (worse than single glaze!)||38||45|
|8.4mm (L) – (12) – 4mm||29||39||52|
|8.4mm (L) – (12) – 8mm||29||40||55|
|8.4mm (L) – (25) – 8mm||29||42||56|
|8.4mm (L) – (100) – 4mm||32 (Good reduction for low freq)||50||60|
|8.4mm (L) – (200) – 4mm||34 (Good reduction for low freq)||56||68|
|8.4mm (L) – (100) – 4mm – (100) – 8mm||34 (Good reduction for low freq)||56||70 (Indiscernible improvement)|
Key Takeaway: When choosing glazing, go for double glazing with the maximum air gap your window sill can afford (up to 200mm).
For single glazing, the simple answer is the thicker the better. However, if you were to dive deeper into the topic, you will find that differing thickness have weak spots at different frequencies. If you are somehow dealing with just a specific frequency of noise in your home (which is highly unlikely), then you will want to avoid the glass thickness with a weak spot that corresponds to that frequency. More commonly, we face noises of all frequencies. Thus, the general principle hold: the thicker the better.
|Glass thickness||Frequency at which sound reduction is poorer (weak spot)|
For double glazing, it is sufficient to follow one golden rule. Make sure the 2 pieces of glass are of different thickness. As mentioned before, there is a weak spot in your glass at different frequencies. Therefore, by using glass of differing thickness, the individual panes take it in turn to manage the weak-spot frequency of its partner.
Key takeaway: Use thicker glass if possible without compromising on air gap. Use glass of 2 different thickness in double glazing.
Air Cavity Filling
When shopping around for double-glazed or triple-glazed windows, you might have noticed that some window systems have an air gap containing special inert gases like Argon. The principle behind this is that gases like Argon have a higher density and therefore can stop sound transmission better than normal gas. Such systems are also more expensive than normal air systems.
Most studies concluded that the addition of Argon has no significant effect on the sound insulation ratings of windows. Paris-Newton’s  study showed that addition of Argon improved the sound reduction by 2-3 dB which is almost indiscernible by the human ear.
However, one thing the Argon air cavity excels in is thermal insulation. If you have an issue with heat retention then this might be the solution to reduce heating costs at home.
Key Takeaway: Choose a normal air cavity as it is cheaper and you get the same soundproofing results.
A commonly overlooked aspect of the window unit is the frame. Although the frame accounts for only a small area of the window unit, it does have a role to play in the overall soundproofing quality of the window unit.
There are 4 materials that are used for window frames nowadays. They are wood, aluminum, polyvinyl chloride (PVC) and fiberglass. We could only find good quality research on PVC and aluminum.
Between PVC and aluminum window frames, PVC performed marginally better in terms of soundproofing [7,9]. In some studies, the difference was too little to discern with the human ear. As such, we would recommend you to choose your window frames based on other grounds of cost, thermal insulation heats, aesthetics and maintenance demands.
Check out the video below for a detailed comparison between different frame materials.
Key Takeaway: Choose the frame material based on your climate, architectural style and budget.
In this section, we will be looking at hinged windows vs sliding windows. In terms of soundproofing, research shows that hinged windows were significantly better than sliding windows. Maraqa’s study  found that hinged windows had STC ratings that were about 6 to 7 dB higher than sliding windows. This is largely due to the superior airtightness and air seal that hinged windows can provide.
|Window Style||Sound insulation||Durability||Air Flow||Ease of cleaning|
Key Takeaway: For sound insulation purposes, choose hinged windows
Now that you have understood all the specifications that are required for your soundproof window, it is time to find a company that can meet your needs. At this point, it would be prudent to seek out companies that have received recognized accreditation that ensure the quality of their products.
As Simon Beer, Managing Director of Bluesky Certification, told us, “Certification schemes usually require their manufacturers to have processes implemented into their factory to ensure that the specification of all windows is as per what is tested. They also require regular audit tests to check that certified products meet the originally tested performance”.
Frequently Asked Questions (FAQs)
Q: What windows are best for soundproofing?
A: Double glazed laminated glass hinged windows. That is the shortest and most direct answer. However, if you want more details for better performance, you can read our guide above.
Q: How can I soundproof my windows cheaply?
A: Acoustic curtains might be the most effective cheaper alternative to true soundproof windows. Studies show that multiple layers of industrial grade acoustic curtains can reduce noise by about 25 dB.
Q: Are triple glazed windows more soundproof?
A: Yes. They are more soundproof than double glazed windows but only marginally by 2 dB. This level of reduction is not discernible by the human ears. However, triple glazed windows cost TWICE as much as double glazed windows.
Wrapping it up
Noise pollution from road traffic, or any other sources for that matter, can severely reduce one’s quality of life. If DIY methods are not working out for you, it may be time to consider real soundproofing windows. The costs may be higher but the improvements you get in sleep quality and health are priceless.
In summary the best soundproof windows should look something like this;
- Double-glazed with glass of different thickness
- At least 1 piece of the glass is laminated glass
- Has a large air gap (more than 50mm)
- Thicker glass if air gap will not be compromised
- Normal air cavity
- Hinged opening
This would give you the best soundproofing results with the best value for money.
 Characteristics of vehicles producing excessive noise and ground-borne vibration – Phase 2, R E Stait, M Clifton, Published Project Report PPR 246, Transport Research Foundation
 Quiet down: Acoustic curtain walls save money & time, J Kyle, Chilton’s Industrial Safety & Hygiene news, Vol 45, Issue 8, p52
 Variable room design In office spaces by the use of sound insulating curtains – Jonas Schira – The Journal of the Acoustical Society of America 141, 3598 (2017);
 Acoustic insulation capacity of Vertical Greenery Systems for buildings, G Perez, J Coma, C Barreneche, A de Garcia, M Urrestarazu, S Bures, L F Cabeza, Applied Acoustics 110 (2016) 218-226
 Sound transmission through single, double and triple glazing. Experimental evaluation, Tadeu AJB, Mateus DMR, Applied Acoustics 62 (2001) 307-325
 Acoustic behavior of high acoustic performance window glazing, Mateus D, Pereira A, Tadeu A, Noise Control Engr J. 61 (3), May-June 2013
 Laboratory testing of different window design cases for noise transmission, MA Maraqa, YS Hawas, MdD Alam, JE Zarif, KN Aljunadi, Materials Science and Engineering 383 (201) 012027
 Improvement of thermal insulation of residential buildings’ facade via acoustic insulation, JAE Paris-Newton, E Prokofieva, N Henry, Building Acoustic 2016, Vol 23(2) 120-128
 Acoustic insulation performance of improved airtight windows, HK Park, H Kim, Construction and Building Materials, 93 (2015), 542-550