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So lockdown has my wife and I starting to look at our condo and start itching to tear it all down and remodel. We’ve been planning for years and had been hoping to hire it all out, but the time has come for us to DIY it (God help us).

Our condo is an old paper warehouse with significant concrete floors and ceilings and concrete pillars holding everything up. The drywall walls between units is not structural at all. We only share one wall with a neighbor, which is built of steel studs and 1/2” drywall, doubled on our neighbor’s side. There are also 2 of the structural pillars that span the common wall, and of course the concrete floor and ceiling. The bottom plate is embedded in the concrete floor.

Our first project is to double the common wall to isolate ourselves from our neighbor as much as possible. The neighbor is a good friend and on board with this project, but won’t let us re-drywall her side.

I've attached a few pictures of the wall from our side. We'll demo everything here as part of this project, so feel free to ignore the bookshelf and perpendicular half wall.

Here are our initial thoughts:

1. remove the drywall from our side of the wall.

2. seal the backside of the neighbor’s wall as best we can.
  • Seal any holes - not sure if any patching is necessary, but there are certainly some drywall anchors and probably a short HDMI run through some sizable holes.
  • caulk (acoustic) and putty the junction boxes and drywall seams
  • caulk (acoustic) around the studs, top and bottom plate
  • fill the stud spaces with insulation (I promise to look up best practices for what kind)
  • considering adding a third layer of drywall to the backside in-between the studs, but that would involve cutting around junction boxes and fitting behind conduit.
  • No drywall on our side — this will be a two-leaf assembly
3. Build a second wall
  • Metal studs
  • at least an inch separation from the original wall
  • caulk under the top and bottom plates, though they’ll be ram-set into the concrete. Same with the edge studs into the end pillars.
  • ensure the electrical is completely isolated/separate from the original wall. We don’t share electrical with the neighbor, but we both have conduit in the shared wall. Most likely, we’ll abandon our conduit that’s there now and run clean lines that no longer touch that wall.
  • Fill in insulation in the new wall (somehow - not yet sure how to do that without drywall on the back side)
  • On the front side, double 5/8” drywall, green glue, offset seams. With the separate studs, my understanding is that isolation clips would be superfluous
  • caulk (acoustic) the seams and edges of the drywall

Our goal here is as good as we can reasonably get, and better than the shared wall we have now. No home theater in this immediate space -later, on the other side of the condo from this wall, we’ll build room-inside-a-room theater, but that’s for another post. We’ll isolate subwoofers from the floor/ceiling as best as we can, but we won’t be aiming for reference levels in this space.

Happy to hear what we’re missing, what bad assumptions we’ve made, and any tips we should keep in mind.
 

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RETIRED theater builder
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Sounds like a pretty good plan, the unknown is what sound is being transmitted via the floor and ceiling. Concrete is actually a pretty good conductor of sound. The good news is that it has a lot of mass so it is hard to energize. If you have any concerns of sound leaking from your unit to your neighbor you could add rubber pads under/over the top and bottom plates of the new wall you plan on building. That will keep wall vibration from the floor and ceiling. Unless you know otherwise there is a chance that the wall between your unit and your neighbors is not a simple double sided single framed wall. There may be a fire rated middle layer. That effectively makes it already, triple leaf wall.

One last note, you may need approval from your condo association for wall modifications
 

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Discussion Starter #3
If you have any concerns of sound leaking from your unit to your neighbor you could add rubber pads under/over the top and bottom plates of the new wall you plan on building. That will keep wall vibration from the floor and ceiling.
Excellent idea! Any suggestions on what kind of rubber I should look into?

Any thoughts on the usefulness of trying to add another mass layer to the back of the neighbor's drywall in between the studs? My idea is to add more mass, but I'm not sure how to affix it other than drilling short screws into the drywall. I don't expect green glue would hold it on its own. I could use a more robust adhesive and skip the GG on that side. Anyway we do it willl be tedious, but I'm more than willing if it'll make a difference.

As for the internal wall construction, I'm quite sure it's single stud, having been inside of it before. And both me and the neighbor are on the condo board, so we've got approval taken care of :D

Thanks again!
 

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One last note, you may need approval from your condo association for wall modifications

You will need a few things. Do not ignore these things as they have the potential of impacting your pocket and time in a very serious way. Trust me.



  1. Because this is a multi-family building you are going to need a permit from the city or county where you live for this work. Even before removing any drywall.
  2. Because this is multi-family you will not be able to pull the permit and do the work unless you have a light commercial license.
  3. You must get HOA permission before any of the work. Also, read the declarations and bylaws carefully. Sometimes the common walls are HOA property. Sometimes its just the walls that have common area on either side and not between units.
  4. Obtain the building plans from the city or county using an open records request. Looks fairly new so they are likely to have them. You are going to need them for the permit process and they may show hidden plumbing or electrical etc in the wall. They aren't always accurate and don't describe the 'as-built' structure, but they can help.
 

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RETIRED theater builder
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Excellent idea! Any suggestions on what kind of rubber I should look into?
Any thoughts on the usefulness of trying to add another mass layer to the back of the neighbor's drywall in between the studs? My idea is to add more mass, but I'm not sure how to affix it other than drilling short screws into the drywall. I don't expect green glue would hold it on its own. I could use a more robust adhesive and skip the GG on that side. Anyway we do it willl be tedious, but I'm more than willing if it'll make a difference.
Horse stall mats from Tractor Supply are a good source of thick rubber mat. Gyms going out of business can be a source of rubber mat flooring, you want something at least 3/8 thick. You can cut with a hook nose blade in your utility knife

It doesn't take a lot of screws to hold up the extra drywall until GG turns into a "glue" use 1 inch screws for adding 5/8 drywall to the back of your neighbors. Start at the bottom and let gravity do the heavy lifting, then build up. Don't over sink the screws they can sit on the surface.
 

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Horse stall mats from Tractor Supply are a good source of thick rubber mat. Gyms going out of business can be a source of rubber mat flooring, you want something at least 3/8 thick. You can cut with a hook nose blade in your utility knife

It doesn't take a lot of screws to hold up the extra drywall until GG turns into a "glue" use 1 inch screws for adding 5/8 drywall to the back of your neighbors. Start at the bottom and let gravity do the heavy lifting, then build up. Don't over sink the screws they can sit on the surface.

I really mean no offense by this as I think the suggestions will work. When it comes to multi-family and meeting code and permits etc to ensure the HOA is protected and the other homeowners are protected etc etc blah blah it helps to use products with ratings and documents to include in any permit applications and for inspections.


An example of a product for wall isolation:

https://kineticsnoise.com/wallmat/stud-wall-isolation.html


The contractor that will do this work will also need engineering drawings unless this city is pretty relaxed with its requirements.


I read through the posts, but didn't really get a sense of what the sound objective was... Do we get noise from the neighbor or do we want to keep from annoying the neighbor?


I own two condos with very similar loft design and have worked through sound issues on them.
 

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RETIRED theater builder
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EAS, good points. As I reflect on this project if the city inspectors accepted single framed wall as suitable for partition walls in a fairly recently constructed condo project they really aren't keeping a sharp lookout for appropriate building methods. More leeway might be possible but needs to be determined to avoid legal issues.
 

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EAS, good points. As I reflect on this project if the city inspectors accepted single framed wall as suitable for partition walls in a fairly recently constructed condo project they really aren't keeping a sharp lookout for appropriate building methods. More leeway might be possible but needs to be determined to avoid legal issues.

A single wall with two sheets of drywall on one side likely met the fire rating (assuming the right rating for the drywall product) at the time of construction. Not the best solution for sound, but the rating was probably met. These conversion projects meet the letter a lot of the time, but fail to meet the spirit of the code. Developers are cheap and double walls cost more money and since they can meet code with less they have a hard time justifying the cost. Also, lofts are noisy by nature. Floor strikes telegraph and sound from the hall carries. Why soundproof a wall when the noise goes around?


The condo docs for my lofts literally state that the lofts will be noisy and there is no expectation of quiet enjoyment. My tenants love them and know what they are getting into for that period of their life. Most of my tenants end up married and buy a house with a yard and privacy. Pretty stereotypical.


Unless the OP is dealing with a nuisance from a neighbor I'd consider the value of the effort. Sometimes moving can be more effective.
 
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