Soundproofing Spray Foam for Existing Walls

by Jennifer Porterfield | Last Updated: July 7, 2021
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As a popular construction material, spray foam is used in home construction for the thermal insulation of walls. It can be bought in most home improvement and maintenance stores as well as hardware and building supply centers. The main purpose of this spray foam is to keep your home warmer in winter and cooler in summer. Yet it is also being used to control noise since it forms an extra sound barrier between connecting walls.

The thickened walling is sturdier and more difficult for sound waves to penetrate. When it is used as a soundproofing material, this product is called acoustic spray foam. It helps in absorbing sound and reducing noise in your home interiors. Many homeowners and renovators prefer this material to use sound reduction wall panels or noise suppressing paint.

This effective spray foam is made from polyurethane, and it may be closed or open-celled. Its components include Polymeric MDI and a blend of polyol resins as well as fire-retardants, surfactants, and various catalysts. The fire retardants are important for inhibiting combustion and smoke, and the surfactants act as blending agents and emulsifiers.

Sound control experts may advise you to consider other methods for effective noise reduction in your home. However, when soundproofing spray foam is used for sealing gaps and cracks in walls and around window frames, it can eliminate some external noise from entering your rooms completely.

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The Two Variations of Soundproofing Spray Foam

The two varieties of soundproofing spray foam in use today in home construction and wall renovations include the following:

Closed-Cell Spray Foam

This variety of spray foam is composed of polyurethane with closed cells. This foam is heavy, dense, and rigid. The closed cells have a compact structure and admit very limited amounts of air and heat to pass through them. This type of foam resists water and will help keep your room interiors free of humidity and moisture accumulations on surfaces.

The compact closed cells permit only a small degree of foam expansion equaling about one inch. This feature helps maintain the firm, dense quality of the foam for reinforcing wall construction and sealing cracks.

Open-Cell Spray Foam

Most of the features of open-celled spray foam are the exact opposite of those of the closed-cell variety. This open-cell foam is quite light, and it can expand as much as three inches. Open-cell foam is also very flexible, enabling users to seal extremely small cracks in walls and surrounding windowpanes. It also seals crevices and gaps surrounding door and window frames securely.

This type of spray foam is especially effective for general soundproofing purposes due to its thickness. It is also significantly less costly than most closed-cell spray foam. To serve two home improvement purposes well, ensure that the open-cell foam that you select offers high performance for both thermal insulation and sound reduction.

The Meaning of Different Acoustic Spray Foam Sound Ratings

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There is a set sequence of values and metrics to use for measuring the intensity of sound. Following this sequence is essential for effective soundproofing results. The two most valuable measurements are Hertz and decibels. While Hertz calculates the sound frequencies, decibels determine the intensity of the volume of sounds and noises.

When soundproofing existing walls in your home, the most valuable sound measurements are STC and NRC. STC is short for Sound Transmission Class and determines the effectiveness of varied materials for decreasing sound transfer. The greater the STC count, the fewer the degrees of sound that are being measured. This means that outside noise is being reduced and the sound control method being used is effective.

NRC is an abbreviation for Noise Reduction Coefficient, and it determines how well a material absorbs or reflects sound waves that strike it. It measures in Hertz, and the higher the final number is, the better a given material is for sound absorption. It is helpful to compare the STC and NRC of open-cell and closed-cell spray foam.

Open-cell foam is known to expand by three inches when it is applied to an existing wall. It offers an STC equaling 37 to 39 as well as an NRC of 0.70. Closed-cell foam, however, expands just one inch at application, and it offers an STC of 36 plus an NRC equaling 0.70.

These results reveal that closed-cell spray foam is not very effective for dampening exterior noise from the opposite side of a wall. Open-cell foam is definitely the better choice for use in soundproofing walls in your home.

Three Effective Ways to Use Noise Control Spray Foam on Existing Walls

The following are three efficient and effective ways to use sound control spray foam on your existing walls:

1. Sealing Cracks and Crevices in Walls

Approximately 50 percent of common noise can penetrate your walls through cracks and crevices. When you seal all of these weak spots and gaps with effective spray foam, you can enjoy more peaceful home life. After the foam expands, fills all the cracks, and dries, you can add additional soundproofing materials if you like. These materials may include acoustic foam panels, wallpaper, and soundproofing paint.

You can also use acoustic foam panels in combination with soundproofing foam to increase the absorption of interior room noise. By suppressing both interior and exterior sound, you can enhance the quality of your home’s rooms for reading, studying, conversation, and sleeping.

2. Apply Spray Foam Between Drywall

By applying the noise-controlling foam spray between the drywall, you can reduce sound vibrations from exterior wall contact. The foam between the drywall helps absorb and lessen the sound waves’ level, making your rooms calmer and more inviting. Be sure to use open-cell foam spray to ensure excellent filling and sealing of weak points that let outside sounds enter your room interiors.

Newcomers to DIY home soundproofing techniques may find using foam spray somewhat messy and time-consuming. Yet with a little patience, they will realize its effectiveness and cost savings as a home soundproofing method.

3. Use Foam Spray Around Acoustic Panels

If you are installing acoustic foam panels on a wall, try spraying foam along the edges of each separate panel. If you are covering a large area of the wall with a set of these panels, it helps to spray around the entire set of panels. This will seal any small crevices, cracks, or gaps and aid in preventing or decreasing the level of sound transferred from outside.

An alternative method is to close the gaps and cracks with foam spray before installing the acoustic panels. You will need to wait for the foam to dry before applying the panels. However, you will benefit from more thorough soundproofing when the job is finished. Foam noise reduction spray is versatile since it can be used in combination with sound suppression paint with good results as well.

How to Get Ultimate Noise Reducing Results from Foam Spray

Because walls have hard surfaces, vibrations and noise can travel through them with ease. Yet when soft, pliable, and spongy-like materials like foam spray are applied to them, quality soundproofing can be accomplished. Foam panels for noise dampening are composed of soft, flexible, and absorbent polyurethane, which lessens both initial sounds and echos.

We now know that soundproofing spray foam used alone cannot be expected to provide the ultimate quality sound deadening. Yet when used with other effective sound suppressing methods, it offers a valuable foundation. The foam spray supports and enhances the efficiency of the other methods for successful absorption and reduction of sound waves.

For example, you can seal all cracks and crevices in the walls of a room with soundproofing spray foam insulation containing polyurethane foam. This increases the strength and solidity of the walling. Next, you can add as many as three layers of sound reduction paint for dampening any external wall noises. Since this paint is quite thick, multiple layers will effectively decrease sound wave transference from outside.

After the paint dries completely, you can apply a series of acoustic foam panels to strengthen the soundproofing effectiveness. Place the most panels on the wall areas that receive the greatest levels of sound impact and transference. This savvy mix of noise suppression methods and materials can keep your home’s interiors quiet, even when exterior sound increases.

Know the Difference Between Sound Deadening and Soundproofing

If you soundproof a room in your home, you block all unwanted noise from entering the room. No airborne noise that originates outside of your room will enter the room through your walls, ceiling, or flooring. Sound deadening suppresses sound transfer into your room. With the use of injection foam in your walls, you can lower the sound transmission by at least 80 percent.

Whether you decide to soundproof your room completely or simply dampen incoming sound waves depends on the room’s purpose. A music practice room for the talented young music students or accomplished musicians in your household needs soundproofing.

If this room is your family entertainment center where you watch favorite films and videos, you want to soundproof. However, if the room is your family’s leisure, relaxation, and gaming area, noise reduction is most likely adequate.

FAQs About Using Soundproofing Spray Foam in Existing Walls

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Should You Choose Injection or Spray Foam Insulation for Dampening Sound?

The major advantage of using foam insulation to deaden unwanted exterior sound in your home is its easy installation. It can be installed in your existing walls without demolishing or damaging your drywall.
Installers can remove a siding panel, drilling a hole in the stud cavity. They can then inject the foam. By skillfully moving the hose from top to bottom, your installation team can be sure that the cavities are full of foam. Then the crew members close up the hole and replace the siding panel.
Injection foam is used successfully in both external and internal room walls. When used between the drywall, it can lower the noise level from one room to another significantly. Spray foam insulation is a good choice for dampening sound through a ceiling if you have an attic in your home.
The attic roof deck is usually insulated, yet that does not guarantee that the attic floor cannot be insulated as a choice. Your final decision will be dependent on what you are using the attic for. It will be based on what you use the attic for today and whether you wish to have it sealed off from the remainder of your home.

Can Foam Spray be Used to Reduce Sound in Rooms with Cathedral Ceilings?

Soundproofing spray foam insulation is also quite effective for use in reducing sound in a room with a cathedral ceiling. First, your expert team will cut panels into the ceiling. The installer then sprays the foam into the ceiling cavities. Next, the drywall is replaced and then a rough coating of drywall mud is applied over the seams.
Both spray foam and injection foam fill the cavity where they are added totally. They are both popular choices for superior insulation material for decreasing, but not completely eliminating, exterior noise from your home.

Is Spray Foam Effective for Use in the Walls of an Old House?

Actually, spray foam is not recommended for use in reducing sound transference through walls in an old house. It does not bond strongly with old insulation materials, and it loses part of its effectiveness. Also, when this foam is added to older home wall interiors, excess moisture may be trapped between the drywall.


Soundproofing spray foam for existing walls is not considered an excellent material for blocking external sound entirely. Yet it is quite effective for reducing noise levels from sound waves that penetrate the walls of your home. When used in combination with other noise dampening and soundproofing materials, however, foam spray is a superior foundation to build on.

This modern material is in popular use as an effective sealant for closing gaps, cracks and crevices in walls. It also forms a powerful seal around the borders of acoustic foam panels to enhance soundproofing methods. This product is also often used in conjunction with soundproofing paint. The use of spray foam as a valuable element in a soundproofing or noise reduction plan is likely to continue well into future years.

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