The Best Insulation for Soundproofing: We Compare Types

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. It 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 soundproof 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 soundproof 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 soundproof 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. The denser and thicker 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.

What Is Noise?

We all think we know what noise is, but not everyone realizes 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).

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 Sound	Approximate Sound Level in Decibels
The softest sound audible to the human ear	0
Breathing	10
A whisper	20
Background noise in a library	30
Light rain	40
Normal speech	50
Traffic	60
Hairdryer	70
Blender	80
Power tools	90
Motorcycle	100
Rock concert	110
Thunder	120
Ambulance siren	130
Jet engine taking off	140
The chest begins to vibrate	150
Eardrum bursts	160

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 soundproof 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.

There are a lot of misconceptions about soundproofing, and the most serious one is the word itself. Although everyone calls it soundproofing, 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. Unfortunately, no matter how well you follow best practices for mitigating noise transmission 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 movement of the building fabric itself initiates the vibrations.

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 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 noise. 

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

Factors to Consider When Choosing a Soundproofing Insulation

While it’s clear that soundproofing your home with an insulator is essential for your peace, you want to get the best overall option for your home. Therefore, it’s necessary to acquaint yourself with some key factors to consider when heading to the hardware. 

The most important factors to consider when choosing a soundproofing insulator include:

Noise Reduction coefficient (NRC)

While most people consider the R-value when looking for heat insulation materials, you should be more focused on NRC as your aim is to achieve a quieter home.

NRC is the most essential factor to consider in sound insulation. It determines the material’s ability to absorb sound and is given on a scale of 0.0 to 1.0. A rule of thumb is to go for a material with an NRC above 0.45.

R-value

While this is not essential in soundproofing, it’s worth it if you want to maintain a comfortable indoor environment by retaining more heat.

An insulator with a high R-value offers more resistance to heat flow, maintaining a comfortable indoor environment and lowering your energy bills in the long run.

Allergens

If you or another family member is sensitive to various products, you should understand these triggers before installing any sound insulator.

STC

It determines the insulator’s efficiency in blocking sound. The higher the STC rating, the better the insulator for soundproofing.

Sustainability

If you’re an eco-friendly homeowner, a sustainable insulation material is your best bet. If that’s the case, you can go for cellulose, fiberglass, mineral wool, and cotton.

Application

The different types of sound insulators are installed in different ways. Some of the application processes are more complex than others.

Therefore, it’s essential to consider the difficulty of installation when selecting your material. This is especially crucial if you want to go the DIY route.

Fire Resistance

An acoustic insulation with a fire retardant is the ideal option if you’re looking for a fire-resistant material.

The Best Insulation For Soundproofing

The best insulation for soundproofing is a contentious subject.

Every contractor has their own 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:

• Identifying the problem areas: Identify the areas where noise is most problematic. Such areas could be exterior walls, ceilings, floors, or even doors and windows. Different areas may require different types of soundproofing materials and techniques.
• Measuring and planning: Measure the dimensions of the area you want to soundproof and calculate the quantity of materials you’ll need. It’s crucial to have enough material to adequately cover the entire surface area. Make a plan for how you will install the materials.
• Preparing the surface: Ensure that the surface you’re applying soundproofing to is clean and in good condition. Remove any existing wall coverings, drywall, or obstructions that may hinder installation. Repair any damaged surfaces and fill any cracks or gaps. 
• Adding mass: 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. You can also use resilient channels to decouple the drywall from the structure. This prevents sound vibrations from traveling through the building structure.
• 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. You can use acoustic panels or insulation boards for this.
• Testing for effectiveness: After installation, conduct a sound test to ensure your soundproofing efforts are effective. You can play loud music or create noise in one room and check for sound leakage in the adjacent room. 
• Monitoring and making the necessary adjustments: Keep an eye (and ear) out for areas where excessive sound may still leak. You may need to make adjustments, like adding more soundproofing materials or sealing gaps as necessary.

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

Different spray foam manufacturers use various foam formulations, resulting 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.

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 interior 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.

Typical Rockwool (or mineral wool) insulation batts 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 walls.

Construction materials are rated in acoustic 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 reduce noise, an STC rating of 40 and above can be achieved using 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.

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.

As you know, replacing old and failing insulation is recommended before putting in new ones. You can use our guide on How To Remove Old Cellulose Insulation!