When soundproofing my home office and my son’s band practice space, I wanted to know “does spray foam insulation reduce noise?” I checked out open and closed cell spray polyurethane foams (SPF) to see if I could use it for thermal and acoustic insulation.
Does spray foam insulation reduce noise? Based on my research, the easy answer is no. Open cell spray foam performs better than closed cell, but neither is effective at blocking sound transfer. The qualities that make it an excellent thermal barrier also create disruptive resonance and its adhesion couples the wall elements together increasing noise transfer.
Some of my friends and clients expressed an interest in what I was doing, so I figured I’d share my findings. Hope they assist you in controlling noise intrusion in your home or office.
What is Spray Foam Insulation?
Spray foam is an open or closed cell polyurethane material that is made of two components that mix when sprayed onto walls or into wall cavities. It expands to cover a surface or fill a crevasse or cavity before hardening.
One part of the liquid spray is polymeric MDI (methylene diphenyl diisocyanate), and the other is a blend of polyol resins, fire-retardants, surfactants, and catalysts. The fire retardants decrease the combustibility and smoke generation.
Closed Cell
Closed cell spray foam expands between 35 and 50 times its original volume and weighs about 2 lb/ft³ when hardened. An ozone friendly hydrofluorocarbon is commonly used to deliver the mixture to the wall surface or cavity where it expands and hardens.
Over 90% of the cells are closed making the foam impermeable to moisture and vapor, and improving its thermal values. It has an R-value of 6.1 per inch of thickness. The hardened polyurethane has a tensile strength of 28psi and is much less compressible or flexible.
The greater strength offers advantages in hurricane or earthquake prone areas to help secure wall and roof components together.
Open Cell
Open cell polyurethane foam expands to 150 times its original volume and weighs about 1/2 lb/ft³. Water is used to drive the blended materials onto the wall or into a cavity where it expands to form an open-celled matrix that remains slightly compressible and flexible.
The interconnected open cells trap airflow making it a good thermal barrier. It blocks air flow and has a thermal R-value of 3.6 per inch, but is semi-permeable to moisture and vapor. It has a tensile strength of 4.0psi.
Airborne and Impact Noises
There are several types of noises we try to control in our homes or offices. Airborne and impact sounds are the two we normally attempt to control with insulation. Soundwaves are vibrations that travel through the air until they encounter an obstacle – wall, tree, window, person, etc. The frequency wave vibrates its way through the object and continues.
Some of the waves may be absorbed or reflected, so less travels onward, which can reduce the intensity of the sound. The barriers don’t usually work on all frequencies, absorbing some but not others.
Low frequency sounds from drums, and bass instruments take a lot to decrease. We’ve all felt them reverberate through walls and vehicles. Mid-range and high frequencies tend to be easier to mute.
Impact noises occur when something hits a surface inside or outside a structure. They are also known as structural sounds. Foot-falls on hardwood or concrete can echo through a building.
Bouncing a tennis ball or basketball against the wall or even on the driveway reverberates into the building the same way. The impact initiates the airborne vibration through a barrier into another space within your home or office.
What Do The Sound Ratings Mean?
The sounds we hear usually range from 20 to 20,000 Hz; age and other issues factor into the range we hear too. 0 decibels is essentially silence. The rustle of leaves is between 10 and 20 dB, a quiet home or office is 40 dB, and the average street noise or a party between 75 and 80 dB. A bass drum, jet engine or car horn can be an ear-splitting 130 dB.
Hertz (Hz) is used to measure frequencies of sound waves, and decibels the loudness heard or intensity produced by different sounds. The STC measures how different materials or barriers interact with 16 different frequencies. The NRC how much sound intensity they block.
Sound Transmission Class (STC)
The STC is a value used to rate how effective different materials or combinations of materials are at improving the sound transmission loss (TL) in decibels (dB). It rates the movement of 16 common frequencies between 125 Hz and 4,000 Hz through the materials or assemblies. The less sound measured going through, means the greater the transmission loss, and the higher the numeric STC rating.
Noise Reduction Coefficient (NRC)
The NRC is a number system used to rate how well a tested material absorbs or reflects soundwaves. It represents the average tested absorption results of four common frequency ranges – 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz.
The average is the NRC value and is rounded to the nearest 0.05 between 0 and 1.0. The greater the value, the better the material is at absorbing or reflecting sound.
Does Spray Foam Insulation Reduce Noise?
To soundproof a partition wall, consider the structure and weight of the material you want to use. We know we need to absorb, block, and damp the sound waves, plus decouple the layers to stop sound transfer through the wall. Some materials have NRC and STC ratings that help us out, and you can read about it in my post about soundproofing insulation options.
When we apply what we know about open and closed cell polyurethane we can also understand why it may not be good for soundproofing. Although it has good thermal properties, it doesn’t have the mass to absorb soundwaves.
The hardened foam forms a rigid material that also interferes with absorption. Couple the harder material with open or closed cells, and you get increased resonance whereas a softer more airy substance will damp it.
The property that makes the spray foam good for hurricane and earthquake zones is also what makes it bad for decoupling. It secures wall components together, so that sound vibrations can move through more easily. The wall construction, the thickness of the foam, and wall sheathing influence performance too.
Comparison of How Insulation Improves the STC Rating of a 2”x4” partition wall with 1/2″ drywall on both sides and an initial STC between 33 and 35
| Insulation | Thickness | NRC | STC |
| Open Cell Polyurethane | 3” | 0.70 | 37-39 |
| Closed Cell Polyurethane | 2.75” | 0.70 | 36 |
| Rockwool Safe’n’Sound Batten | 3” | 1.05 | 45 |
| Rockboard 60 | 3” | 1.10 | 52 |
| Owen-Corning R-11 Batten | 3.5” | 0.95 | 39 |
| Owen-Corning Fiberglass 703 | 3” | 1.10 | 52 |
As you can see from the comparison table, spray foam is not the best material for sound insulation. Closed cell spray foam insulation has the lowest noise deadening ratings.
Open cell polyurethane spray foam performs better with noise reduction and comparable to fiberglass batten insulation. Both types of foam largely underperform compared to Rockwool and fiberglass rigid insulation.
Although the values should indicate an improvement in the sound attenuation of a standard 2×4 partition wall, the adhesion of the foam to the components allows soundwaves to pass through easily.
Additionally, the open and closed cells in the hardened foam increase mid-range frequency resonance distorting the sound quality. It has excellent thermal performance, but comparatively not a good soundproofing material.
Spray Foam Insulation Cost
Open cell polyurethane spray foam is less expensive than closed cell. The cost of the material depends on where you live, and if you plan to install it or have the pros. Some places give the cost per board foot and others by square foot at R-1. However, I prefer a 1-inch thick square foot price.Polyurethane Foam Insulation Cost
(Not including labor)
| Insulation | Cost per Board Foot | Cost per Square Foot at R-1 | Cost by Square Foot 1”x12”x12” |
| Open Cell Polyurethane Foam | $0.40 – $0.75 | $0.12 | $1.00 – $1.20 |
| Closed Cell Polyurethane Foam | $1.00 – $1.50 | $0.20 | $1.25 – $1.50 |
Better Alternatives for Soundproofing
There are alternative insulation products that can be used instead of polyurethane spray foams. They have excellent thermal properties like the foam but have even better soundproofing abilities.
Retrofit:
Trying to improve the soundproofing of existing walls can be a challenge. Blown in cellulose insulation is 75-85% recycled material and is an excellent sound absorbing material that reduces feedback, and mutes echo.
It comes in two formats – loose fill which is less expensive, and dense fill. Loose fill has an STC of 44 and an NRC of 0.80, while the dense fill has an NRC of 0.90 and STC between 44 and 68 depending on how dense it’s packed.
New Construction:
New construction offers a blank slate for soundproofing. Metal or wood studs, isolation clips and channels to decouple layers, mass loaded vinyl, Green Glue for damping, newer construction techniques, and your choice of insulation.
It’s easier to soundproof from the start than to retrofit sound control in later. Two helpful articles you may find interesting are How to Soundproof Walls and Soundproof a Basement Ceiling.
- Fiberglass
Fiberglass battens and panels insulate and also soundproof more effectively than foam. Owens Corning 703 Fiberglass Panels are 2-inches thick and have an NRC of 1.10 and an STC of 52. The panels can be used on the wall or inside the cavities. It absorbs sound, reduces echo, and control reverberation.
- Stone Wool
Stone wool is available in insulating boards and battens too and is also better for controlling sound than the spray foams. mineral wool insulation is 2-inches thick, has an STC of 52, and an NRC of 1.10. Like fiberglass, it reduces echo, controls reverberation, and absorbs sound.
Conclusion
Polyurethane spray foam is great thermal insulation and it does have some soundproofing potential. Unfortunately, the characteristics that allow it to trap soundwaves also create a resonating chamber that seems to amplify mid-range frequencies which are disruptive.
Additionally, the hardened foam also binds layers together which couples the wall elements and can increase sound transfer. If you found this article of interest and you know someone who might appreciate it, pass it on. Your comments and suggestions are appreciated too.
Hello I want to ask you, with open cell pu foam, how’s soundproof how ?
1 inch pufoam soundproof how many db?
Great article.
Noisy neighbors are killing us in our duplex. We have a massive ‘A’ frame style attic which I think echoes and amplifies sound. I’m thinking of some sort of baffle system to help reduce bounced sound and changing the ceiling insulation.
Ron P
Papercrete is a good option for those who don’t want to spend a lot and have permission to make small holes in the wall. Just make a couple of 3″ (or larger) holes in each cavity, mix up the paper and cement ($3 – $7 per bag at Home Depot) into a mash-like slurry and start shoving it in, making sure that it goes in in small enough globs to fall to the bottom, then patch the hole with joint filler and paint. It sounds more tedious than it is and though I’ve not done any sound level readings, I hear my neighbors a lot less.
The paragraph about NRC uses the unit dB. I think you meant to use Hz (abbreviation for Hertz, 1 cycle per second).
Noise Reduction Coefficient (NRC)
The NRC is a number system used to rate how well a tested material absorbs or reflects soundwaves. It represents the average tested absorption results of four common frequency ranges – 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz.
Correct, thank you!
This is helpful information. We have spray foam (not sure closed or open; new construction 2017) in our unfinished attic and we have lots of noise transfer seemingly coming through the attic from room to room on the main level. There’s almost an echo while on the main level of the house. Can you please suggest anything to dampen the sound in our home? Thank you in advance.
Do you think the tiles of soundproofing foam you attach to the ceiling are any good. I need to soundproof a floor/ceiling. My brother resides in the bed sit below my bedroom and I can hear all the noises he makes. Including snoring.
Good explanation. Needs to add the reduction potential by 1/3 octave bands because there might be an application for a select band of frequencies of interest for noise reduction.
My neighbor’s new AC unit is right outside my office window. It puts out a sound frequency that is annoying inside my house. The AC company said “sorry” that’s just the way it operates. Our houses are both brick and only ~ 20 ft apart. I’m thinking of building a 6′ x 10′ fence between the unit and my house. The fence will have wood slates on both sides with either fiberglass or stone wool insulation, enclosed in plastic, inside. Any thoughts about why this wouldn’t work or any better ideas?
Thanks. The article was very good, just what I was looking for.
Larry
Hi Eugene. I own a duplex rental property built 1958 as CHEAP as possible. Bedrooms share a common wall. I want to sound insulate between the two homes to provide a better living situation.
One thought was to cut existing drywall along verticle studs and push that material + more drywall to fill that cavity & re-drywall finish surface, texture & Paint. There is a drywall on the market that deadens sound better than 5/8″ drywall ($60+ a sheet).
What are your thoughts?
Wow exactly the info I needed and very well put together with a thorough analysis! My man! Thank you!
Amazing info for a beginner like me. Super helpful. Thank you for taking the time to share…
Wood home furniture possesses something incredibly organic about
it. There is this feeling of warmth, of nature as well as of
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Hardwood is actually born coming from the earth.
Hi Eugene,
Wondering if you have any data sheet or something listing the STC of open-cell spray foam? Looking for some kind of official documentation, none of the spray foam data sheets I’ve found list STC at all.
I can’t believe there isn’t paneling or something you can put on wall that would look nice and provide some insulation from thin cheap construction walls in a condo. It seems so simple but all you see are ugly panels to hang on your wall, who wants that…..no one.
Similar to the ceilings but on a wall.
Hi Karen, I have no expertise in this area so I will only be giving you “paraphrased” information that I received from our local Building Code Official (I was the Fire Marshal at the time so I had direct access). We have several Naval facilities in our region with lots of noisy jets. Anyhow, I was told the two best options were to either use two sheets of drywall (one on top of the other rather than just a single layer) or purchase some speciality drywall that was designed by the manufacture just to address the noise issue.
Here is another cavat: the conversation referenced above took place in 2010 a few months before I retired. Good luck
I have a 4″ drain in a closet, and I’ve wrapped it with some sound deadening mass vinyl, but it has some branches in the line, so it’s hard to completely wrap it.
I’m putting in a new interior in the existing closet, and was planning on just filling the space around the pipe and the wrapping with some Great Stuff foam, as I build in the closet.
I think your article is suggesting that instead I should get https://www.lowes.com/pd/ROCKWOOL-SAFE-n-SOUND-R-Stone-Wool-Batt-Insulation-with-Sound-Barrier-23-in-W-x-47-in-L/4382951 and use that instead? It’s pretty darn tight, so I’m concerned there won’t be much space to get it in. It might be easier to work with though…!
Thoughts?
Hi Eric,
Spray foam is not your friend when it comes to soundproofing. It will help some when filling holes where pipes penetrate walls. Here a few space-saving ideas:
1) Install as much Rockwool as possible in the cavity. Do not pack it tight. (Tighter will reduce soundproofing.)
2) Install a sheet of Mass Loaded Vinyl over the studs before drywalling.
3) Hang a soundproofing blanket either inside on the studs before drywalling, or over the wall after it is finished.
4) Double 5/8″ drywall with Green Glue sandwiched between is probably the best choice because of the extra mass and lack of space you have to work with. You can still install rockwool before drywalling for a bit more.
Hope one of these will work for you,
Terry
My bedroom shares an existing wall with some noisy neighbors. In addition to hanging MVL sheets and sound blankets like a giant curtain in front of an exiting shared wall, I was thinking of filling any gaps between the drywall and the electrical boxes on that wall (and whatever I could reach behind the boxes using the straw) with low-expansion spray foam. Now I’m not sure that is a good idea. Any suggestions on how to retrofit to help soundproof around the existing electrical boxes?
Hi Lisa,
Foam is not the greatest soundproofing product, but anything that fills the holes is better than nothing. You will probably not be able to fill behind the boxes. Any foam you spray into the wall cavity will hit the opposite drywall and slide to the bottom. My preference would be to caulk around the box with acoustic caulking (assuming the drywallers were any good and the gap is less than 1/4″). Then install a Trade Gear Wall Plate Insulation Gasket (Amazon) before putting the cover back on. You can put a small bead of paintable caulking around the plate if it does not fit tight.
You will get way more gaskets than you think you need, but acoustic caulking never dries so if you ever remove them, you are going to throw the old one away. They are universal and will fit regular duplex outlets, GFI outlets, and switches.
Hope that helps,
Terry
Thank you. I’ll try the gasket and caulk.
Rather than hanging whole sheets of sound deadening material i was thinking of facing the metal studs with strips of it before the dry wall goes on. And then use green glue with another layer of dry wall board. Or am i wasting my time?
It is a cargo trailor conversion to be used for camping/ sleeping and for work at a desk. So the quieter the better! (Even white noise machines are very irratating for me! Unfortunately!!!)
Thanks for your time!
Hi Paul,
Unfortunately you will be wasting your time and money. Sound travels through gaps. If you are going to use something like Mass Loaded Vinyl cover the entire wall or don’t bother. Double drywall will Green Glue will help a lot because of the added mass. Spray foam on the metal walls should help with the vibration effect and it will act as a vapor barrier on the steel skin. Not sure where you live but up here in the frozen north, condensation is a real problem with steel shells.
Hope that helps,
Terry
would foam injection into masonry blocks help reduce noise?
I was planning on injecting foam into the blocks on a new construction house then insulate with, either spray foam or insulating panels, in between the block and the sheetrock from the inside.
Hi Esteban,
Injecting foam into the concrete block will not help very much (STC rating of 36 – 39). If I were doing it, I would use cellulose blow-in insulation (STC rating of up to 70). I am assuming you are going to either strap the inside of the block or build a 2 x 4 wall on the inside to accommodate insulation and drywall. 2″ Rockwool batts between the strapping will give you the best soundproofing option. Spray foam on the inside of the wall will be less effective for soundproofing, but will provide good insulation value.
Hope that was helpful,
Terry
Cellulose blow in insulation blown in between nyc noisy neighbor shared wall would have STC up to 70 and what would the NRC be? Am I reading that to reduce noise, cellulose blown in insulation would be best bet? With the insulation now in the wall would the noise vibrate off the material and transfer sound in? Looking to mitigate in apt shared wall and best material without adding mass or draping MLV entire wall. Some helpful and economic Suggestions Questions for a contractor coming to give estimate
Hi Maura,
According to the Cellulose Insulation Manufacturers Association NRC can be upwards of 0.80. Cellulose is way better than foam, and better than many other products. Cellulose cuts down vibration and sound transfer. Your contractor should have some experience doing this. Not just someone who rents a machine and blows stuff in. He needs to cut about a 2″ x 4″ hole at the top of the wall between every two studs, drop the hose to the bottom of the cavity, and pull it out slowly as he is blowing to get a good job. And turn the air down on the blower unless you want the stuff blasting back through the hole and filling your place with a whack of dust. If it is just blown in at the top, the cellulose will get hung up on electrical boxes, wires, plumbing, and even nails that missed the studs giving you areas in the wall that have thin insulation. Then he should have the talent to patch the holes.
Hope that is helpful,
Terry
I wish I had known this sooner. We peeled off a layer of fibreboard and a layer of shiplap board in order to spray foam between the studs from the outside. Now our place is an enormous sound attractor. Outside footsteps, coughs, car doors, everything is audible.
Any idea on what we can do to remedy the situation? Peel off the siding, frame an extra layer of studs with Rockwool? MLV inside or outside? An extra layer of drywall inside with green glue? An extra layer of OSB outside?
Thanks for your help.
Hi Fred,
Sounds ugly. Like living inside a bass drum. But you probably get good insulation R-Value, so tearing it all out again to replace it with Roxul rockwool soundproofing batts (although and option) is probably not very attractive. I think you need to decouple the wall by using sound isolation clips c/w hat channel. Then dry wall with either 5/8″ soundproofing drywall like QuietRock or Certainteed, or double 5/8″ standard drywall with Green Glue sandwiched between. Another option is to build a room-within-a-room that is not connected to the existing walls in any way. You can take a look at our article ‘How to Build a Room-Within-a-Room‘ for more information on that type of a project.
You could add plywood or OSB to the exterior. But if I were considering that, I would put a layer of QuietRock on the existing sheathing first to add soundproofing mass, then sheathing, then re-installing the siding. This does not provide the decoupling but the added mass may be sufficient. And you do not need to tape and mud and paint, or extend electrical boxes and window and door jambs.
Hope that helps,
Terry
Hi,
There is a swimming pool above my room, i can hear low impact noise when there are people kicking or making deep splashes in the pool. Is there any way for me to soundproof the ceiling of my room to reduce the noise? Thank you.
Hi Tommy,
Best bet is probably to decouple the ceiling with either resilient channel or isolation clips and hat channel. Then install QuietRock drywall or double 5/8″ drywall with Green Glue sandwiched between. It is a little pricy and time consuming but will do a very good job of decoupling, adding mass, and damping the noise. Both the Green Glue and the viscoelastic layer in QuietRock will damp sound. You may want to take a look at our article QuietRock vs Double Drywall and Green Glue – Which is Better for more information. Or How to Reduce Noise from Upstairs (10 Effective Ways).
Hope that helps,
Terry
This blog is spot on, and I wish I had read it before renovating my house! We demolished everything down to the studs and filled the stud cavity with around 3” of closed cell insulation, and put regular 1/2” drywall in the inside. We have a busy street nearby, and the first night of sleeping in our renovated house, I was woken up by the cars from the morning rush-hour traffic. The fiberglass insulation we used to have did a better job keeping out noise. My heating and cooling bills are a lot better, but now I have to sleep with a white noise machine, and I am currently trying to figure out ways to improve the STC rating of my exterior walls. Any ideas?
Hi John,
I am sure you are not interested in spending the time and money to rip it apart again. Adding a layer of 5/8″ drywall with Green Glue sandwiched between the existing and the new drywall will add extra mass and the Green Glue will help dissipate some of the noise. For more information please see our article 15 Ways of Soundproofing Existing Interior Walls Without Removing Drywall.
Terry
We moved into a new condo this past year. We easily hear noise from our upstairs neighbor ( who is not noisy!)… footfalls, TV etc. We know that she can hear sound from our unit as well. Do you think that cellulose blown into our ceiling would help with this?
Hi Marianne,
Blown cellulose is an excellent sound reduction product. It can increase your STC rating by up to 44. See more on cellulose STC and NRR here. What you need to get is a professional installer who will cut the hole in the drywall, run the hose the full length of the ceiling cavity, turn the air down, and fill it properly. You do NOT need some stud muffin who is going to cut a hole, stick a 3″ hose about 2′ into the cavity and let ‘er rip. This will leave unfilled spots as the product tries to get to the far end without blow back, and around nails, screws, and other obstructions.
Terry
Amazing information for all my customers that are looking for Soundproofing and Acoustical Absorption for apartment and houses in New York
Hi Milton,
Glad you liked it.
Terry
Hi Terry,
We have a house with a unit underneath. I have just had spray foam insulation sprayed under the house for insulation ( the house is cold!) but as we rent the unit less noise is also an aim. We did not put spray in the gap between the floor of upstairs and the unit ceiling below. This is the area we most want to soundproof. It is a 10m x 4m area with the joists running width way (4m) we can access the end of all the gaps. I was thinking of getting soundproof spray blown in. Thoughts please
regards
Steve
Hi Steve,
Blow cellulose, not foam. Foam does not work as well on sound. Cellulose is great for sound. When you blow it, (you can rent machines and buy the product from Home Depot for sure, maybe Lowe’s) push the hose to the far end, turn the air down, and slowly retract the hose as it is filling the cavity. If it starts blowing back at you, the air is still too high.
Terry
Hi Terry,
We have a home that is on pilings that you can park under. We had the house spray foamed, open cell under the house and in the attic and closed cell in the walls (unfortunately). We can hear cars drive by like they are in the house.
We built a drop down ceiling under the house to put our soffit up and to try and reduce the noise further we bough tons of rockwool Site and Sound. My question: Should we lay the Batts on top of the drop down ceiling frame, or jam them against the spray foam that are in the rafters. I wasn’t sure if the 4 inch airgap space between the dropdown and spray foam would be a better reducer of sound. Thanks for your time.
Amber
Hi Amber,
The rock wool will absorb noise with or without the air space. But I would probably lay it on the drop ceiling rather than against the rafters. Rockwool will lose some of its absorptive qualities if it is compressed too much.
Terry
Very helpful article, thank you! We are renovating a 1922 duplex right now, and removed the plaster ceilings in the first floor unit (where we will be living) so we can install sound barriers. We are thinking of rock wool + resilient channel + 5/8 drywall. Do you know if open cell foam would be able to replace the rock wool in this design, or if it be significantly less effective? The floor joists are not all 16″ on center (they can range from 16-20 and are not uniform, as it is an old house before those were standardized), which makes rock wool installation more challenging, especially around pipes. Can we do a combination of rock wool and open cell? I am also wondering if I should have opted for the hat channel + clips, rather than the ‘z’ channel design. Any insight would be appreciated, thanks!
Hi Mizu,
Give some serious consideration to spraying wet cellulose on the ceiling before re-finishing it. Sprayed in cellulose does not care about uniformity and will seal very well around the pipes. It has an STC rating of 44 and an NRC rating of 80–depending on floor thickness. One of the reasons for the high ratings is that it fills every nook and cranny.
I like hat channel and isolation clips better because they provide better decoupling than resilient channel. It also just seems way sturdier to me.
Terry
Hi Eugene,
I live in a residential area and we can hear cars speed by. I had a professional come and test what he was going to do in one room before we did all the walls facing the street. He went down to the stud and did a whole bunch of things. Happy to send you work proposal. I want to sort out this issue but feel lost. Not sure what direction I should go. Would love to chat with you for a few minutes, if possible