Effect of Insulation in the Common Wall

Lets take a look at the effect of insulation in the common wall based on tests conducted at Orfield Labs (an NVLAP accredited lab) and at the labs of the National Research Council in Canada.

Insulation is a valuable, even invaluable, tool in the battle to isolate sound, but in the conventional wall the performance that it offers is limited. The reason for this is as follows

Above we see two walls, one a conventional wall with drywall screwed directly to a single row of studs, and the other a staggered stud wall. Sound can pass through these walls via the air in the cavity (red lines) or via structural paths (blue lines). The staggered stud wall has less mechanical connections than the conventional wall, and sound cannot easily pass through the structure. The same applies as when we decouple the wall with Whisper Clips. In the conventional wall, vibration/sound can easily pass directly through the studs, and does not need to go through the air cavity to be transmitted to the other side.

Adding insulation absorbs sound that is trying to pass through the air in the cavity, but has no effect on structural noise. In the staggered wall, with less structural noise, insulation has a distinct positive effect at middle and high frequencies, but in the conventional wall, where structure-borne noise is strong, the effect is far less.

EXAMPLE 1 - Data from Orfield Labs

Effect of insulation in a conventional wall

B oth walls are constructed with a single layer of 5/8” drywall screwed directly to 2x4 studs spaced 24” on center, the difference being the inclusion of R13 fiberglass in the “with insulation” example.

Its worth noting that at both low and high frequencies, the effect of the insulation is minimal – the primary gains coming in the lower midrange.

The overall improvement in STC is just 3 points, from 37 to 40, and gains at low frequencies are non-existent.

Now lets take a look at another example, this time from the NRC labs in Canada, one of the finest labs in the world. This data is taken from IR-693 and presented here with the NRC’s permission:

EXAMPLE 2 - NRC’s lab, taken from IR-693

Effect of insulation in a conventional wall

The comparison shown here is as above, but with studs at 16” on-center. Both data curves can be found in IR-693, available at www.nrc.ca.

The effect is very similar – the largest gains are just above the primary low frequency resonance, low frequency gains are non-existent, and high frequency gains are very minimal. In this case, STC rises again by just 3 points.

Often it is thought that using denser insulation is the cure-all to sound problems. But this simply isn’t the case. In general, it is preferable to use standard building type insulations (i.e., normal fiberglass) and it is never desirable to utilize expensive, very dense insulations, as in addition to the expense, they tend to make low frequency performance worse by raising resonance frequencies.

This comparison is taken from IR-761 and IR-693, both available at www.nrc.ca, and courtesy of the National Research Council, and shows the comparison of no insulation to mineral fiber that is considerably denser than the fiberglass used in the comparisons above.

This data is taken from IR-693 and presented here with the NRC’s permission:

EXAMPLE 3 – Comparison with Dense Insulation.

Effect of adding layers to a normal single wood stud wall

In this case, the gains in the midrange are higher than with conventional fiberglass (denser insulations do have proven advantages at middle and high frequencies), but low frequency performance isn’t as good as with the lighter insulation, and STC rises by just 2 points, from 32 to 34.

Where insulation has much more value – in decoupled walls.

In walls in which the mechanical connection between the two sides, insulation has proven, and considerable, benefits at middle and high frequencies. However, at low frequencies the capacity of insulating materials to absorb sound falls dramatically, and the benefit of insulation at low frequencies is to lower resonance points. Still, lowering resonance is valuable, and in walls with damping or decoupling, insulation has considerable value at middle and high frequencies, and should be considered mandatory for any sound isolation application.

To imagine how insulation becomes less effective as frequency falls, think of this experiment – place fiberglass in front of the mid/high frequency speakers in your room, and listen to what happens. The sound will probably be very muffled and muted. Now put the same fiberglass in front of the subwoofer cones… nothing happens. So it goes with walls.

As we mentioned above, the use of insulation is a critical, and valuable, part of any sound isolation project, but insulation alone can’t win the war, especially in the conventional wall where direct structural connections exist between the sides. The main winner will still be a damping compound like Green Glue that stops the structure as a whole from vibrating.

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Customers Questions and Answers

1) steve: I am remodeling a guest room and bath adjacent to my room, and want to the sound transition as low as I can, and afford. I have opened the walls, so have an opportunity to make a good effort. I think I will use your putty pads around existing elect boxes, and on a cold air return duct which are in the shared wall. then build another decoupled wood framed wall with double 1/2' sheetrock with green glue compound between layers, and green glue caulking all around. Should I use the G.G compound on the studs prior to the wall board installation? And will the putty pads be an effective product for the cold air return duct? We have a lot of mechanical noise coming thru the under slab C.A. return ducts as well! Do you have any suggestions for mitigating this noise? Baffles with little air restriction? Thanks

Trademark Soundproofing Reply:

Hi Steve, The Green Glue on the studs will not offer much benefit so save your money and skip that. I would not use drywall between the new wall and the existing wall rather only on the outer side of the new wall in order to avoid the Triple Leaf Effect. Putty Pads would help slightly however they are not a damping compound and will not do much to damp the ducts. We will have a new product in 2016 for this application, stay tuned. Thank You

2) Doug A: I purchased a 22 unit apartment complex that is noisy between the wall units. I discovered that there is no insulation in the walls. What do you recommend I do to damping the sound in the walls. Would blowing insulation in the walls help Doug Anderson

Trademark Soundproofing Reply:

Hi Doug. It would help however not enough to be worth the effort. I would suggest you blow insulation into the wall and then cover with a 2nd layer of drywall and Green Glue Damping Compound.

3) E. P: Have noise problem between walls in a brand new reconstructed farmhouse. We took it down to the studs. Walls and ceilings are butt joined painted wood and floor is also wood. Builder sprayed all walls with icynene telling us everything that is spray foamed will be soundproofed! My husband and I can carry on a conversation with each other when one is in bed in the the master bedroom and the other in the guest bathroom directly behind the bed. Help!!

Trademark Soundproofing Reply: Hi, That is unfortunate. We hear that from many customers and have mentioned it in our articles, spray foam can actually sound worse many times because it glues all the building components together. At this point your best bet would be to add another layer of drywall with Green Glue to your existing wall.

4) Paul : I am putting In a new subfloor In about half of my main floor and want to add green glue between my 2 plywood sheets to reduce noise between the main floor and basement unit. Does it make sense to use green glue only on half the floor? Will the sound from the basement simply come through the part of the floor that doesn't have green glue installed ? I can see that it would only reduce structural vibrations from the main floor from transferring to basement on the areas it's installed. Thanks for your insight! I will be filling 100% of the floor with blown fibreglass.

Trademark Soundproofing Reply: Hi Paul, I would not recommend that as the sound will come through the untreated part. You want to cover the entire envelope/floor.

5) franco: i just bought a home next to a 4 lane road. the noise from road is crazy. what is the best solution. what insulation product works the best for road noise..spray or batts? please help. we are considering insulation and adding another layer of drywall

Trademark Soundproofing Reply:

Hi Franco, Fiberglass is better than spray foam and adding a 2nd layer of drywall with Green Glue will help a lot. For the windows you can use our window panel barriers. Thank you

6) Joshua E: I am building a soundproof booth to record music. I was going to put joint gasket tape on the studs. Use roxul rockboard as insulation and double sheetrock and green sealat between the seems. I am also using professional soundproof padding on the sheetrock. Am i heading in the right direction. What would you suggest?

Trademark Soundproofing Reply:

Hi Joshua, You should use the Green Glue damping compound in between the 2 layers of drywall and the Green Glue sealant at the perimeter.

7) Mike: We just recently moved into a house with our bedroom facing a road. It is fine most of the time during night. However, in daytime, whenever there're pick-up trucks accelerate on the road, we can hear the rambling engine sound pretty clearly. After reading into your website, I'm considering to approaches. Option #1. Blow in cellulose insulation into the wall (currently no insulation in exterior wall), and add another layer of drywall with green glue. Option #2. Take the existing wall out, add fiber glass bat, put in clip and channel for decoupling, and add two layers of drywall with green glue. Of course, the option#2 would be much more costly. Do you think it is worth the effort and money to go the extra-length? What would be the low frequency performance difference between the two options? I'm looking to reduce the truck rambling noise by half if possible. Thanks. Mike

Trademark Soundproofing Reply:

Hi Mike, If you will be happy with reducing the noise by half then Option 1 would work. If you are looking to do the most possible then option 2 would be the way to go. What are you planning to do for the windows? Take a look at our sound control window panels.

8) Jeremy : Hi. I have a new construction home and there is no insulation between the floors. At night I can hear my tenant snoring. When they move out I really want to do some notice control. Any suggestions. Thx

Trademark Soundproofing Reply:

Hi Jeremy. I would suggest you rip the ceiling down and start over with insulation, clips, channel, drywall Green Glue and drywall. You can read more details here http://www.tmsoundproofing.com/How-to-Soundproof.html

9) BLM: I live in a townhouse complex and I own my unit. I constantly have excessive noise from my neighbors that the HOA seemingly can do nothing about. I do not know what to do. I redid the whole place in late 2012/early 2013, but was not having this issue at the time. The problem occurs when they are watching a movie or playing games and their surround sound system is turned up. The bass noise is the main problem for me. It affects my chronic headache condition. What can I do to alleviate this noise from coming through? This complex was built in 1983 and I do not even know if there is any or what rating of insulation is in the shared wall.

Trademark Soundproofing Reply:

Adding a layer of drywall with green glue damping will help tremendously with low frequency sound. See more details here http://www.tmsoundproofing.com/soundproofing-existing-rooms-walls-ceilings.html

10) Cameron: I am building a room for a dog kennel that will house around 10 or so puppies, in the corner of my garage, that will use the two existing outer walls and two new walls will be framed in to complete the room. What would you recommend for this since the noise will most likely be at a higher frequency? Thanks!

Trademark Soundproofing Reply:

Hi cameron. I would suggest insulating the walls. Using 3 layers of half inch drywall with 2 layers of the green glue damping compound in between and then having a sound absorber like this one on the walls http://www.tmsoundproofing.com/Sound-Absorber-Long-Term-Applications-Exterior-Grade.html

11) Peter T: I live in semi detached new home. In the basement I hear next door neighbors kids noises. We have concrete wall between and standard flooring. How can I remedy this problem?

Trademark Soundproofing Reply:

Hi Peter. You would have to For proper soundproofing you would need to build some sort of wall/ceiling frame that you can install insulation into. Then cover with 2 layers of 1/2" drywall with the Green Glue damping compound in between. You can read more on our how to soundproof existing walls and ceiling article.

12) Malcolm: I have converted my garage into a living space with a ductless heat pump. I am preparing to general contractor come in and spray foam inside the exiting walls and upper ceil area. How can I now soundproof the garage? Thanks,

Trademark Soundproofing Reply:

Hi Malcom, Please see this soundproofing article. Thank you.

13) Saul H: HI, i have an existing wall between two units and only have access to one side. I will not be able to open the existing wall to fill it with insulation to help with soundproofing. Would it be better to just apply two layers of drywall with green glue on my side, or should i apply resilient channels, sound isolation clips, roxul, and 1 layer of drywall? Thanks

Trademark Soundproofing Reply: If you are removing your existing drywall to install insulation then it would be a very good idea to apply clips and channels. You can add 2 layers of drywall with Green Glue onto the channel for best results, however even 1 layer will be very good.

14) Saul H: Hi. We are not removing the existing drywall. Is it better to Install a resilient channel with roxul over the existing drywall or apply two layers of drywall with green glue directly onto the existing drywall. Thanks

Trademark Soundproofing Reply:

2 layers with Green Glue directly to the wall as you do not want to run into an issue we call the triple leaf effect.

15) Gary B: We are building addition to our church, 9500 sq. ft. with basement under for class rooms. We have 12" deep floor joists. Would two layers of 5/8 rock with green glue between be better then 12 inches of blow in insulation. How much better? Advise needed. Thanks, Gary.

Trademark Soundproofing Reply:

Hi Gary. You really need both Insulation and 2 layers of drywall and green glue. One without the other will not do enough.

16) Timothy R: We own a first floor condo with another unit above. The existing ceiling has dry wall with clips and batt insulation, but we hear almost everything from above. They have hard wood floors and we hear every step they take. Would having foam insulation added be worth the money or would we need to do more to reduce the noise level to an acceptable level. We know we would not be able to totally eliminate the noise, but would really love to muffle it as much as possible.

Trademark Soundproofing Reply:

Foam insulation would not be worth the money (may make it worse). If you have clips and channels on the ceiling already with fiiberglass insulation your next best step would be to add another layer of drywall with Green Glue Damping Compound in between. You may also have a flanking sound issue as in soffits or walls. Footstep sound from hardwood floor above is very difficult to control without treating the floor itself.

17) lorrie d: I own a townhome, I share walls with my two neighbors, both have stairs on our shared walls. Stairs are very noisy, I hear talking, cubboards shutting, tv, music. What would you suggest doing to these 2 walls that I share with my neighbors ?

Trademark Soundproofing Reply:

That is a tough one as their stairs are attached to the shared wall. You would need to decouple your wall and treat it. See this how to soundproof a wall article explaining how that is done.

18) Joel S.: We are building a semi-custom home and the contractor is giving us a few options. Which of these are most effective to soundproof between the first and second floors? R19 with 3" thermafiber, R19 Fiberglass insulation (batts) or soundboard (homasote). Also for the basement ceiling/first floor we are doing green glue, should we also to R19 thermafiber or is that enough? In general, what is more effective for noise? Soundboard or fiberglass? Thanks!

Trademark Soundproofing Reply: You have to have fiberglass/mineralwool insulation for absorption as a starting point, however insulation in itself is not enough. Green Glue without insulation behind it loses a lot of it's performance.

19) Matt W: Hi, I am trying to make a new room sound resistant. I have Roxul Safe and Sound and 1/2 inch Dow Super R Tuff foamboard. I used both of these together in the ceiling with an air gap in the middle. For the 2x4 walls though, I am not sure if I should just use the Roxul, as it is designed for 2x4 walls, or also add a layer of the 1/2 inch Dow Super R Tuff but that would make it very dense.. There will be a surround sound system in the room. Any thoughts you could provide ASAP would be great! I could also use 1 inch Dow Super R Tuff instead of 1/2 inch but i think that would just make it even more dense.

Trademark Soundproofing Reply:

Packing the insulation is not a good idea. Leave it to fit the cavity it is meant too. Either way once you use insulation it mostly done and adding more insulation will not be of great benefit. rather you should add decoupling or damping on top of the insulation. See this article http://www.tmsoundproofing.com/How-to-Soundproof.html

20) Joe : I am building a new house with a theatre room / bar room combo. Theatre in back, bar towards the front. This room is on the end of the house with no 2nd floor and only 1 wall (entry wall with bar side) attached to the rest of the house. Only two small windows and a sliding a 10 ft sliding door on the other. What should I use to insulate affordably and give me the best chance for quality sound when listening to music or movies? Thank you JOE

Trademark Soundproofing Reply:

For soundproofing standard fiberglass or mineral insulation is fine. However for proper soundproofing you will need to add to this. See our how to soundproof a home theater article for details.

21) Jacob: Hello, I am building a basement apt and I'm really worried about sound noise from my tenant coming up into my house however I do not have the ceiling height needed to add a second layer of drywall in the basement. Would adding a single layer of drywall and green glue under my sub floor before laying down my insulation help?

Trademark Soundproofing Reply:

It would help, a little. Probably not enough for what you are worried about. You can use 1/8 of an inch thick Mass Loaded Vinyl stapled to your studs before installing your single layer of drywall. (Make sure there is insulation before you install the MLV).

22) Mary: Hi, I?m in a condo with a unit above, we have concrete ceilings and drywall. We are not allowed to drill into ceiling so what would my best option be to control footfalls and scrapping furniture? I plan on adding wood planking to the ceiling so I can either remove drywall and start from scratch or add to existing drywall. Any help would be greatly appreciated. Thank You, Mary

Trademark Soundproofing Reply:

Remove drywall. make sure there is insulation in ceiling. Add resilient sound clips with channels. Follow with double layer of drywall with the Green Glue damping compound sandwiched between the two layers. See details in this how to soundproof a ceiling article. Thank you.

23) Adam R: We are building a Multifamily apartment and would like to know if the STC rating changes if the batt insulation is laying on RC channels at 12" on center as opposed to having the batt pinned to the subfloor material above.

Trademark Soundproofing Reply: hi Adam. Won't make much of a difference. You'll get an additional 2-4 STC points either way.

24) Susan B: Live in a first floor condo with neighbors above. We hear everything! They are replacing carpet with hard wood and are using pro flex 90 and an underlayment but offered to lift up floor plywood to do more soundproofing. Our ceiling (drywall), 2x8 floor joist and their plywood flooring is all that is there right now ????? What is the best option to keep out their noise (voices and footsteps?????

Trademark Soundproofing Reply:

Once they lift the plywood. Install Insulation in the ceiling joists. Put down Joist gasket tape on top of the joists, reinstall Plywood, add Green Glue Damping compound and a 2nd layer of half inch plywood.

25) Matt: I am working on a commercial property that is having sound issues between tenants. In the basement is a gym that plays very load music during workout sessions and right above is house of prayer. The ceiling of the gym is pre-cast concrete t-slabs. The slabs are constructed with 16” x 16” arches on the under side. I understand using green glue to fill the seams and any gaps around penetrations through the floor. But filling the voids completely with open cell spray foam won’t help? What would be some other options then? (Hanging anything on the bottom of the concrete is not an option)

Trademark Soundproofing Reply:

You want to fill voids and gaps with Acoustical caulk (not damping Compound). Closed cell may help as well. Either way for proper soundproofing you should consider treating the floor above if you cannot attach anything to the ceiling below. Acoustical panels on the wall will mitigate the sound somewhat.

26) Pavel : Hello. I live on 21 floor in a building. There are 2 HVAC units on top of me on the roof separated by one foot of concrete slob. I suspect low frequency noice is coming from duct behind the wall. What is the best way to reduce the noice? I plan to build a second wall with a green glue. Should I put some sound insulation between the existing wall and a new one? Thank you

Trademark Soundproofing Reply:

That is recommended. At least six inch thick insulation. If you do not have that much room than use three inches of the Roxul Insulation.