Sound reduction options for rowhouse shared wall

[branimal]

I'm framing out a wall that is shared b/w two buildings. I'd like to reduce the sound being transmitted from the neighbor. They have a staircase adjacent to this wall. The wall has an abandoned fireplace that juts out about 4" off the main wall. (See pic.). I'd like to use one continuous top and bottom plate so the wall is flat. Yeah I'll lose a little space, but that's not a big deal in this particular room.

I'm thinking about using 2x6 framing. The top and bottom plate will get notched out for fireplace. 2x6 studs in the deep areas. And 2x4's on the flats (1 1/2) along the fireplace.

In b/w the 2x6 studs I can use 6" SafeNSound (if I can find it near me -doesn't seem to be readily available). In between the 2x4s along the fireplace I can use Sonopan 3/4" panels.

The wall is getting covered up with 2 sheets of 5/8" drywall with some type of sound deadening adhesive in b/w the layers. Can't recall exactly what its called.

Does this sound like a reasonable plan? Any modifications?

Thanks.

 

[WildBill]

If possible I always try to isolate the two sides by using staggered 2x4s on 2x6 base/top plates. Then weave insulation between the 2x4s. In this case with the brick (if I understand it all correctly) you could just have 2x4s pulled forward on 2x6 top/bottom plates across the "face" of the wall and nothing touching the brick, letting you do solid insulation behind the 2x4s. Hopefully that makes sense.

 

[CMB41]

I would use 2x6 bottom and top plates and stagger 2x4 studs every 12 inches ( if code allows) One stud lined up with the front edge, the next lined up with the back, and so on.
Make sure you fill any cracks in the bricks with Green glue or some other acoustic sealant. You are “ decoupling” the brick from the stud wall and creating air gaps. If you are not concerned about thermal loss then I would use loose insulation dumped in behind plastic or ideally behind 1 lb/ ft MLV sheets. Sheets should be attached with screws, not adhesive. MLV tape over seams. Double 5/8 gypsum board over this, also staggered, so seams don’t line up. Acoustic sealant all around. You will get some vibration from the top and bottom plates but it should be negligible.

All this said, you should start with a sound meter and record the actual dB of people walking down the stairs. This setup may be total overkill if the source is not that loud to begin with!

 

[rdoty]

Stagger studded walls as mentioned. Two layers of 5/8" drywall will help a lot. Stagger the seams between the layers of drywall. Wouldn't hurt to glue the drywall sheets together with construction adhesive. Look into sound insulation clips between the studs and drywall. Fill the stud bays with the heaviest material you can find - rockwool or dense pack cellulose will make a big difference.

Air seal everything - air leaks are also sound leaks.

 

[carlaisle]

Steel studs are significantly better at sound attenuation than wood. If you have room for 2x6s you have room for resilient channel, which will help that much more. Dense pack cellulose is more effective at blocking sound than rock wool. Double drywall layer. Don't forget the green glue in between layers. Don't use the lightweight drywall - that's counter productive to your objective. No construction adhesive - that's the opposite of what you want to do. MLV works well if your wallet can shoulder the bill. I'd skip the sonopan.

 

[CMB41]

Echo the no construction adhesive. ( see what I did there). You want air gap and isolation between layers. 5/8 board as mentioned. Have not used resilient channel with steel studs, likely overkill. With a staggered setup the difference between steel and wood is likely less apparent.

I meant dense pack cellulose when I said”loose insulation” as opposed to rock wool battens etc. Thanks to @carlaisle for jogging my brain for accuracy!

one other thing about steel studs. Lighter is gauge is preferable. Counterintuitive in terms of mass but they are more flexible. This enhances decoupling

 

[yhprum]

Your question reminded of this episode.

This may be the adhesive for the drywall?

https://www.greengluecompany.com/noiseproofing-products/compound

 

[billconner]

I respectfully disagree with the "no adhesive" between layers of gwb. The greater mass of the two or more layers laminated together will improve the isolation. 3" of plaster would be even better.

 

[dscheidt]

I respectfully disagree with the "no adhesive" between layers of gwb. The greater mass of the two or more layers laminated together will improve the isolation. 3" of plaster would be even better.

Green glue is a lot better than actually gluing the layers of drywall together, it creates a flexible joint between them, which provides a level of decoupling that a solid wall doesn't have.

@branimal use 2x4 on your 2x6 plates, 24" on center. If you do dense pack insulation, you'll fill the space behind the studs, you will get better decoupling. You could also use 2x4 plates, set back from the wall as if they were a 2x6. This isn't a structural wall, it's only got to hold itself and whatever you hang on it up.

 

[BobnCO]

The green glue works well, I used it for sound mitigation between floors in my house. The double wall staggered stud design is most common when both sides are open. In this case the “double” wall is the brick wall, so a well designed single wall, double rock with sound attunuating adhesive, like green glue, is likely going to be very effective and consistent with published designs.

 

[rlitman]

If possible I always try to isolate the two sides by using staggered 2x4s on 2x6 base/top plates. Then weave insulation between the 2x4s. In this case with the brick (if I understand it all correctly) you could just have 2x4s pulled forward on 2x6 top/bottom plates across the "face" of the wall and nothing touching the brick, letting you do solid insulation behind the 2x4s. Hopefully that makes sense.

It makes sense when you're framing a new wall that will have sheetrock on both sides. It makes NO SENSE in the context of this thread, where you have a brick wall on one side and a new sheetrock wall going over it.

Advice on creating isolation is good TO A LIMIT. Isolating one side from another helps. Adding an isolated intermediate layer actually makes the problem worse, as it creates a membrane that picks up sound. Resilient channel recommended here for instance would isolate the interior sheetrock from framing that is already isolated from the noise producing wall.

@branimal. I like your plan, but it has a few gaps.

1) Air sealing. Sealing up ALL cracks in the brick is where you should start. I'd hate to muck up all that nice brick with spray foam, but that would be the easiest and fastest option. Going to town with a bucket of mortar might be a better long-term solution. Caulk the perimeter and any wood-brick connections where movement might open up gaps.

2) More dampening. It's easier to get a layer of something like MLV (or acousti-lead) in there before framing goes up, and covering that wall with MLV (taping up any gaps) will do more to block the sound than everything else you're doing.

3) Caulking. Caulk under the sill plate. Caulk over the header. Caulk all around the perimeter of the framing. Seal up air gaps completely, because they're channels for noise. When I re-did my basement, I bought a spray foam gun and a case of foam cans and spent an hour a day for a few weeks caulking every single seam in the underside of my tongue and groove subfloor, and as bad as wood is as a sound isolator, just that one step made a huge difference.

4) Don't forget the openings. Electrical boxes let sound through. They make putty for this, but an extra piece of MLV over that goes a long way.

5) The staggered stud plans suggested above (and below), while not relevant to you, do make use of insulation BEHIND the studs and not just in between them. You don't want the studs tight to the brick behind them, and you don't want to bridge that gap with caulk, but closing up that gap with rockwool is probably a good idea.

4" SafeNSound is carried at Home Depot by me, 6" can be harder to find. I ordered enough to cover my basement ceiling in two layers, so I had it delivered. The delivery contractor decided the stacked pallets didn't fit past his truck door, and to make a long story short, it added days that can be an issue when a contractor is waiting on material. You would need maybe a few station wagon loads.

Yes, two layers of 5/8 sheetrock connected with green glue has a great reputation. Do that with the above, and you'll sleep when your neighbor's aspiring drummer kid is practicing with his bandmates.

 

[nadogail]

The two layers of 5/8 drywall with staggered off set studs on 2X6 plates with a layer of Sound Board will attenuate sound transfer.

 

[WildBill]

It makes sense when you're framing a new wall that will have sheetrock on both sides. It makes NO SENSE in the context of this thread, where you have a brick wall on one side and a new sheetrock wall going over it.

Advice on creating isolation is good TO A LIMIT. Isolating one side from another helps. Adding an isolated intermediate layer actually makes the problem worse, as it creates a membrane that picks up sound. Resilient channel recommended here for instance would isolate the interior sheetrock from framing that is already isolated from the noise producing wall.

I am trying to figure out why what I said makes NO SENSE. I recently helped remodel 36 apartments in a brick building, they were originally built in the 40s and had zero sound control measures. Isolating framing from the brick and running rockwool between the brick and the framing made a pretty huge difference in sound, as well as using 5/8" fire rated sheetrock in one or two layers. We also wrapped all the drain pipes and venting in sound insulation and did a isolated two layer ceiling to reduce footstep noise from the apartments above. I don't think OP is making a recording studio, just trying to reduce sound. I know you can spend a ton of time and money making somewhere basically soundproof, and I have done that in the past, but it didn't seem like that was necessary in this case. Not saying your wrong, just trying to figure out why you think what I said wouldn't work. Because I did it recently in 36 apartments, and it did work and made a big difference in sound transmission.

 

[rlitman]

I am trying to figure out why what I said makes NO SENSE.

The part about staggering studs on the plates, so you can screw sheetrock to both sides with each side isolated from each other. There's no point in staggering studs (or using resilient channel) when you're only attaching sheetrock to one side of the wall. It's already isolated.

 

[Bunsen Honeydew]

They are not talking about sheetrock on both sides of the studs, I think.
My opinion, do not let your new framing touch the brick, so that the sounds telegraph through. Insulate with rockwool or similar.

 

[rlitman]

They are not talking about sheetrock on both sides of the studs, I think...

Ok, so WHY would you stagger the studs? The ONLY purpose for doing that would be to have two sheetrock layers isolated from each other.

 

[WildBill]

The part about staggering studs on the plates, so you can screw sheetrock to both sides with each side isolated from each other. There's no point in staggering studs (or using resilient channel) when you're only attaching sheetrock to one side of the wall. It's already isolated.

"In this case with the brick (if I understand it all correctly) you could just have 2x4s pulled forward on 2x6 top/bottom plates across the "face" of the wall and nothing touching the brick, letting you do solid insulation behind the 2x4s"

 

[Rusted Nut]

Lots of good advise from others. Add RC channel to your side under drywall, big sound transmission reduction.

 

[carlaisle]

There is no reason for a staggered stud wall in this application. As noted, that is only applicable for a partition where you want to keep the sound from each room bleeding through to the other. Do make sure the new wall does not touch the existing brick wall and do make sure to thoroughly seal all air gaps in the brick wall before building the new wall.

Resilient channel is still valuable in this application because it provides additional decoupling between the drywall and studs. A single 8' stud has 144 square inches of contact area transmitting sound. When you add resilient channel you cut that down to less than 54 square inches for an entire 4x8 sheet of drywall. That's effectively reducing the contact area by 8 times.

As @CMB41 noted, use thinner steel studs rather than thicker - the thinner gauge is less effective at transmitting sound.

Every air leak is a sound leak. If you have acoustic sealant left over, you didn't use enough. Every penetration avoided in the wall will increase its effectiveness. i.e. Do you really need an outlet right there? Could that switch be on a different wall? etc.

With noise control, not every step provides equal noise reduction per $, so decide on how quiet you need it to be first, then how much you're willing to spend to achieve that objective, and then back into the particulars that make the most sense for your specific project and objectives.

 

[billconner]

You might look at the USG assemblies that show STC for many different wall assemblies.

https://www.usg.com/content/usgcom/en/design-studio/assemblies.html

I was fortunate to work on many projects with the fellow that did a lot of the research and over saw the lab testing of the assemblies at Riverbank Labs.

 

[branimal]

Lots of great advice here. Thanks.

• Studs - I'm going to use metals studs. 3 5/8" along the wall and 1 5/8" along the fireplace. It will it all run in a straight line. (I have metal studs left over from a previous project). 25ga and some 20ga.
• Air gap - check. There will be space b/w the brick and the studs
• Seal brick gaps - I was planning on using mortar mix (Limestone, sand and portland cement) but I've been reading spray foam is more effective and blocking sound. I've got a spray foam gun so I should be able to tackle this fairly quickly.... ****Edit*** I've also read filling the gaps with mortar is better...... So on the fence rn.
• Double 5/8" drywall staggered - check
• Green glue - check
• Safe N sound - They make 3" and 1 1/2" specifically for metal studs. I'll use plastic hanger strap in a "webbing style" to make sure the insulation doesn't fall behind the metal studs.
• MLV looks interesting..... wonder if its overkill at this point?
• Caulk - I can run it under the top & bottom plate, and the wood brick joints.

I started installing the metal track. I also ordered some sound reducing windows.

 

[TRWham]

I have uploaded the SoundBook, which shows numerous options. I think you will find mounting drywall on resilient channels will give you the best results.