Closeup of a hand installing a Rockwool insulation batt on top of a brick wall

After parking, noise is the most common cause of arguments between neighbors.

That’s according to research commissioned by the real estate website, Homes.com, which says 36% of those asked in a poll have had problems with their neighbors that turned into a serious altercation. A quarter of respondents said they currently have a long-running spat with their neighbors.

If ever there was a reason to invest in good soundproofing, keeping on good terms with the folks next door must be near the top of the list—anything for a quiet life (pun intended).

The question is, what is the best way to improve soundproofing in your home?

You might have heard that all you need is a bit of extra insulation in the wall between you and the noisemaker. Still, there are many different types to choose from, and you don’t want to go to all the effort of installing extra insulation only to find that it doesn’t work. 

This article will explain how nuisance noises can get into your home and how different types of insulation reduce the amount of noise coming through your walls.

What is the Best Insulation for Soundproofing?

All types of insulation will help to reduce the amount of noise coming through a wall, and the denser the insulation, the better it will perform. Unique soundproofing insulation materials are available, but wall construction is also essential, especially for reducing low-frequency noise.

Windows are also one of the weakest points in a building regarding allowing noise to enter.

If you are experiencing a lot of unwanted noise outside your home, you might want to consider installing hurricane impact windows, which help reduce this. We’ve written an article on them here if you’d like to learn more.

Looking out from inside a home through a PGT Winguard Energy Star Hurricane Window
Our founder, Erin, installing impact windows in our second Net-Zero home renovation

What Is Noise?

We all think we know what noise is, but not everyone realizes that there is a difference between sound and noise.

In physics, they are the same thing, and people use both terms interchangeably in conversation, but what counts as noise and what is considered sound are open to interpretation. It is in the ear of the beholder, so to speak.

Definition Of Sound

Sound is a vibration propagating as an acoustic wave through a transmission medium.

The transmission medium can be a solid, liquid, or gas, which includes your building’s fabric and the air inside a room, as well as the gap between the leaves of a cavity wall. With so many options for transmission, it’s little wonder that sound can find its way through a home so easily.

Definition Of Noise

Noise, on the other hand, is defined as an unwanted sound. It is any sound unpleasant or disruptive to the peace and quiet one would typically enjoy.

Your definition of “unwanted” could differ from mine, so a sound that you consider unwanted noise might seem to me to be a pleasant sound. A former neighbor and I had a very different opinion about my drum kit. Fortunately, we are no longer neighbors.

How Is Noise Level Measured?

There are two ways to assess noise levels: intensity and loudness.

Sound Intensity

The intensity of a sound is measured in decibels (dB). The decibel scale is logarithmic, meaning that the sound’s intensity grows rapidly compared to the number of decibels.

For example, a sound at 40 dB (such as a refrigerator) will be ten times as intense as a soft whisper, which is around 30 dB, and 100 times louder than a ticking watch at 20 dB.

Sound Loudness

The loudness of a sound is defined according to how loud it sounds to the person experiencing it.

The difference here is that, in a quiet room, a relatively low-intensity sound could sound very loud (think dripping tap in the middle of the night).

Closeup on the head of a faucet with a water droplet dripping off

Whereas an intense sound, such as someone shouting, might not seem very loud if you hear it at a live concert with loud music blaring.

Example Sound Intensities

Here are a few examples of different sounds and their levels measured in decibels to provide some context:

Type of SoundApproximate Sound Level in Decibels
The softest sound audible to the human ear0
Breathing10
A whisper20
Background noise in a library30
Light rain40
Normal speech50
Traffic60
Hairdryer70
Blender80
Power tools90
Motorcycle100
Rock concert110
Thunder120
Ambulance siren130
Jet engine taking off140
The chest begins to vibrate150
Eardrum bursts160

From the description of the decibel scale and the examples above, you can see that a reduction in noise of 10 dB is very significant.

Bear this in mind later when we talk about the relative performance of different types of sound insulation.

What Is Soundproofing?

Soundproofing is a means to cut down the transmission of sound waves through a wall, ceiling, or a building’s fixtures and fittings. Before we get into the different types of insulation and how good they are at soundproofing your room, let’s set some realistic expectations.

Closeup on the texture or pyramid-style foam soundproofing on the interior wall of a home from the edge of the piece

There are a lot of misconceptions about soundproofing, and the most serious one is the word itself. Although everyone calls it sound-proofing, it’s something of a misnomer because you can never fully soundproof a room.

People in the sound insulation business spend a lot of time managing their customers’ expectations. But unfortunately, no matter how well you follow best practices for mitigating the transmission of noise through the walls, floor, and ceilings, you can never isolate it completely.

All you can do is mitigate the factors that cause noise transmission and hope you’ve done enough to reduce the nuisance to acceptable levels. The good news is that often, this is sufficient.

So, what factors allow noise into your home from a neighboring property or an adjoining room in the same house?

Types of Noise That Can Cause Nuisance

The different types of noise that can cause a nuisance to householders come in three basic categories, including:

  • Airborne noise
  • Impact noise
  • Flanking noise

Airborne Noise

This type is the noise that travels through the air. For example, if you have a window open, airborne noise such as traffic noise can enter your home through the opening.

Airborne noises, such as loud voices from a room next door, can be mitigated by placing a sound insulation barrier between the two rooms.

Impact Noise

Impact noise is caused by something hitting another object. Examples include footsteps and slamming doors.

Impact noises are harder to mitigate because the vibrations are initiated by the movement of the building fabric itself.

A heavy boot slamming into a wooden floor will impart more energy into the materials in the floor than someone talking. Therefore, you would hear such an impact more clearly through the ceiling than voices from that same room.

Flanking Noise

Flanking noises are those that travel indirectly from one room to another. It is easy to miss specific pathways that these noises travel along; they can be hard to trace.

Flanking noises can travel along ductwork, through electrical outlets, and any other air gaps that allow noise to leak out. Air ducts interconnect by design, making them an obvious pathway for noises. 

Duckwork that's part of a rigid duct mini-split near a building's ceiling

It’s a popular trope in films for characters to learn something they shouldn’t have from conversations traveling between rooms in the ductwork. And like most cliches, there is some truth at the heart of it.

What Is Sound Transmission Class (STC)?

Sound Transmission Class (STC) is a metric that describes how well a building partition attenuates airborne sound.

STC is a widely-used measure in the US for rating walls, ceilings, doors, floors, and windows. It gives a rough guide to the decibel reduction that a partition delivers for noise at various frequencies. 

The higher the STC rating, the better the sound attenuation. STC works well for the noise of conversation and day-to-day sounds common in the home. 

It’s not so good for noises with a lot of lower frequencies because these will vibrate the fabric of the building in a different way. The types of noise that STC is less suited for measuring include heavy machinery or music with a lot of bass.

Bear in mind that STC-rated partitions are only as good as their weakest link, and failure to complete a perimeter seal or using a hollow-core door can let a lot of noise pass around the structure, causing nuisance despite your best efforts.

What Is a Good STC Rating?

The International Building Code demands an STC of 50 for multi-family buildings. This level is the rating at which most people feel their home is adequately insulated from external noises.

At STC 50, you can’t hear your neighbors talking through the walls, and any loud noises will only be very faint. By contrast, at an STC rating of 30, normal conversation can be heard and understood.

At the top end of STC scores, 60 or above is considered excellent soundproofing. At STC 60, even boisterous speech will be inaudible.

Here’s a table of STC ratings and what you can hear through the partition for each rating:

STC RatingWhat Can You Hear?
25Everyday conversation can easily be heard and followed through the partition.
30Loud conversation is followed. Normal conversation is heard but cannot be followed.
35Loud conversation can be heard but not understood.
40What most people consider to be a good level of privacy.
42Loud conversation can be heard faintly.
45Loud conversation cannot be heard. Most people are satisfied with this level of sound insulation.
50Very loud noises like practicing musicians can’t be heard at all.
60+Excellent soundproofing: hardly anything can be heard, even loud noises.

The Best Insulation For Soundproofing

The best insulation for soundproofing is a contentious subject. Every contractor has their methods and will probably recommend an approach that has worked well for them before.

That’s understandable, but there is more than one way to skin a cat, and it’s possible to achieve the same results using different approaches.

Some common ways to achieve a good level of sound insulation in your home include:

  • Adding mass – this can be as simple as adding a layer of sound-reducing drywall, such as QuietRock, or using mass-loaded vinyl.
  • Decoupling – isolating each side of the wall stops vibrations from propagating the wall itself, which means that noises don’t reach the other side.
  • Insulating the wall cavity – wall cavity insulation prevents any noises passing through the outer layer of drywall from passing through the air in the open space and causing the opposite drywall sheet to resonate, emitting noise into the receiving room. 

Let’s look at some common alternatives for providing sound insulation in cavity walls.

Open Cell Spray Foam Insulation

Spray foam is used on open surfaces, so it relies on having one side of the stud in place before spraying.

The foam expands into the small cracks and spaces in the wall construction, forming a good air seal and preventing noise from escaping via air gaps and flanking noises.

Closeup on a can of Spray Foam Insulation being applied to a door seam during a DIY project

Different spray foam manufacturers use various formulations of foam, which result in distinct STC ratings. It achieves STC ratings of between 40 and 50, which is superb, offering a high level of sound insulation.

Closed Cell Spray Foam Insulation

Closed cell spray foam is applied in the same way as open cell, but it is not quite as effective at insulating the wall from noise because it is less porous and doesn’t dampen the noise in the same way.

A typical STC rating for closed cell spray foam is around 41, about the rating where privacy begins and loud conversation can only be heard faintly.

Blown-In Fiberglass Insulation

If you already have both sides of the stud wall covered in drywall, you can blow in fiberglass insulation through holes drilled in the drywall.

A picture of a man blowing in loose-fill cellulose insulation onto an attic floor.

Adding fiberglass insulation in this way will provide an STC rating of approximately 36. At this rating, loud speech is audible but won’t be understood.

Rockwool Batt Insulation

Rockwool is an excellent way to improve the sound insulation properties of your walls.

It is dense enough to act as a damper for the air mass between the sheets of drywall in a stud partition. Damping the air mass with Rockwool retards sound transmission through the air gap in the wall cavity.

Close-up of worker hands in white gloves installing mineral wool insulation staff in wooden frame for future walls for cold barrier.

Typical Rockwool (or mineral wool) batt insulation like this will get you to STC 50, which is very good. This rating is where very loud noises can’t be heard distinctly.

As a rule, the thicker the insulation, the better the soundproofing. However, the STC rating is highly dependent on the construction of the wall as a whole, as you can see from the ratings suggested here.

Adding extra sheets of drywall can also have a significant impact on the overall STC rating.

Summary

Noise nuisance is a highly contentious issue and is one of the biggest causes of neighborhood feuds in the US.

All types of insulation will help reduce the transmission of noise through partitions in the home, with Rockwool being one of the most effective and excellent values for money.

Soundproofing is a tricky business, and you must temper your expectations because there are many ways for noise to travel around a building. It transmits through not only the air but also the building fabric, such as through timbers in your walls.

Lower frequency sounds are the hardest to mitigate because they travel much further and can come through even the thickest of walls.

Construction materials are rated in terms of sound insulation performance using the Sound Transmission Class (STC) rating system. The higher the STC rating, the better the soundproofing properties of the material. An STC rating of 40 or more is considered to provide a good level of privacy.

Although any insulation that homeowners can add to a wall will help to reduce noise, an STC rating of 40 and above can be achieved using either spray foam insulation or mineral wool.

Blown fiberglass will only get you an STC rating of 36, which will make a difference but falls short of the magic 40 rating for privacy.

If adding insulation doesn’t fix your noise nuisance problems, there are other things you can try, such as adding more mass to the wall, for example, adding extra sheets of drywall or decoupling the drywall from the stud.

And don’t forget to ensure all potential sound leaks are sealed with caulking, especially around the perimeter of your walls which can allow noises to bypass your soundproofing measures.

If you enjoyed reading this article, you might be interested to know that we’ve put together an analysis of the R-values of different types of insulation and how much they cost, which you can read here.

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