Curious: does anyone have experience with having open-cell spray foam insulation pumped into their walls?

Long story short, we moved into a new condo that is absolutely fantastic except for the sound transmission between a neighboring unit. We haven’t cut into the drywall, so we don’t know the insulation situation, but we believe that (a) something is probably there but (b) there are gaps big enough to render it ineffective for sound reduction.

We really, really do no want to tear down the drywall, and we’re not looking for studio-quality soundproofing. Just something effective enough that we don’t hear every sneeze. Our contractor mentioned this as an excellent solution that requires cutting into the drywall but not removing it.

So has anyone tried this? How has it worked?

I did this in my basement. I can't say much about the noise reduction, because it's a brick house. However, one thing you get out of this type of insulation is a very tight seal in your home. The drawback is that you will get a build up of carbon dioxide. So, either you might want to crack your windows from time to time, or get a fresh air system installed to bring in fresh air into your hvac, if you happen to have ventilation instead of radiators. I have an air quality monitor in my basement and it always shows my carbon dioxide in the red when I'm down there woring. Now, I don't live down here, I only work down here, so it's never been a big deal and I crack a window from time to time if I need some fresh air.

Just something to be aware of if you do this type of insulation.

There's also non-spray insulation for the purpose of noise reduction. It's probably a little more expensive. My contractor did me a favor of wrapping my home studio and the bathroom with it. It does a decent job, but depends because my doors also have gaps near the floor, so I can't say for sure how much noise it really reduces.

Thanks—that’s helpful! This would just be for one interior wall, though it’s a fairly long one.

We also haven’t really furnished the room yet or hung anything on the walls. Given that the exterior walls are brick, I’m sure every sound is being amplified.

I had some friends do it for thermal reasons, but not sound. It's an old house with plaster walls so I'm guessing they drilled as small of holes as possible.

But if it creates a tight enough seal that CO2 could become an issue, that's pretty promising for sound transmission purposes.

Wood Goblin wrote: Tue Jun 10, 2025 10:40 am Thanks—that’s helpful! This would just be for one interior wall, though it’s a fairly long one.

We also haven’t really furnished the room yet or hung anything on the walls. Given that the exterior walls are brick, I’m sure every sound is being amplified.

I don't know how they would do spray foam without tearing the walls down first, my only experience was spray foam before we put walls up. I've done blow in insulation this way, but that is totally different, it's just pieces of insulation.

Do you know if the walls are plaster or drywall? I have plaster on my first floor and cannot do blow in insulation because the lathe is 1/4" away from the wall. My house is pretty old, though. If you're lucky, you have a newer home where the framing is done with 2x4s and not 1x2s.

cakes wrote: Tue Jun 10, 2025 11:28 am I don't know how they would do spray foam without tearing the walls down first, my only experience was spray foam before we put walls up.

They cut little chunks out just big enough to fit the sprayer wand in there. I saw my friends' kitchen when it was in the patch up stage.

Most Chicago condo buildings tend to be old but with rebuilt interiors (with the exception of some historic Old Town places maybe). Dealing with modern drywall with studs that are predictably 16" on center would definitely be easier to work with.

penningtron wrote: Tue Jun 10, 2025 11:45 am

cakes wrote: Tue Jun 10, 2025 11:28 am I don't know how they would do spray foam without tearing the walls down first, my only experience was spray foam before we put walls up.

They cut little chunks out just big enough to fit the sprayer wand in there. I saw my friends' kitchen when it was in the patch up stage.

Most Chicago condo buildings tend to be old but with rebuilt interiors (with the exception of some historic Old Town places maybe). Dealing with modern drywall with studs that are predictably 16" on center would definitely be easier to work with.

That’s the case with mine: it’s a converted industrial building with drywall separation between units. (Some walls might be plaster or a different material, but the wall in question appears to be drywall.) Our contractor described the process pretty much the same way: slots cut in the bottom to remove existing insulation (if necessary), and slots in the top to spray in the replacement.

My wife would probably like to hear that CO2 levels can rise, at it would give us an excuse to buy (even more) houseplants.

My place is a conversion of the classic 2 car cinder blocks garage with a flat roof. I had the exterior walls framed, wired and then spray foamed the walls and ceiling. The wall where the doors were became a wood framed wall with windows and a door, again, spray foamed. As others have said, the biggest noise reduction with spray foam comes from the seal. I live a few blocks from the beginning of the industrial area in town and there's always a low level rumble in the neighborhood. That and traffic sounds don't make it into the space. When a drummer is in there I can hear them but it's not loud enough for anyone to complain.
None of my work is super loud so keeping outside noise out is more important to me than keeping inside noise in. Cider block does most of the work. Spray foam does the rest.

Wood Goblin wrote: Tue Jun 10, 2025 12:41 pm My wife would probably like to hear that CO2 levels can rise, at it would give us an excuse to buy (even more) houseplants.

Good thinking!

My studio design brain turned on, but your problem is easier. This would probably help by adding some mass and sealing as stated above. Most builders don't insulate interior walls but it helps for sound.