# soundproofing between suites



## carpentaper (Feb 28, 2009)

I have a little soundproofing job I'm going to price. Its one wall between two suites. The owner wants me to tear down the existing drywall and install quietrock and insulation( if it is uninsulated). There is a door in the middle of the wall . The door leads to a bathroom that we will not be doing any work to because it would cost too much to tear out the bathroom just to install quietrock. 

Building the wall out with multiple layers would be a bit of a headache because of the existing doorjamb. Also there is crown moulding that I would have to replace instead of re-installing the old stuff. I also have to remove a bunch of cabinets tear, down a tile backsplash and then re-install it all after the drywall work is done.

I'm just wanting to know if this job is even worth the money it will cost the homeowner versus the performance of one layer of quietrock.


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## gazman (Apr 29, 2011)

Gday carp. Maybe send off a PM to Ted White. He is our resident sound expert.:yes:


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## betterdrywall (May 4, 2010)

The main problem is the doorjam? Is it metal case? If possible , a person could do a bump out around the opening. and then be able to add extra layers to the wall,not sure if this is metal or wood studs


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## Ted White (Jul 14, 2009)

The #1 thing we want for improving soundproofing is mass. We want heavy stuff. We normally suggest double 5/8" drywall which nets to almost 5 lbs psf. The pre-damped drywall referenced will be much lighter, so sound isolation will naturally be lower. That's why I find factory-damped drywall to be such a waste.

I'm assuming there's no dropped ceiling. That's common.

The door will always be the defining weak link here. It may be a hollow core door (no mass) and isn't likely sealed, so you could install Kryptonite drywall and still not make a difference in the overall isolation. 

Safe to assume the studs are 16" OC? That means any panels applied will not flex much. 24" OC studs allows a lot more flex = higher sound isolation. This is why you see all the lab tests with fctory-damped drywall with 24" OC studs... because they don't do very well on 16" spacing.

If you remove the the existing drywall, how much thickness do you think you can add?


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## SlimPickins (Aug 10, 2010)

I've wrestled with the same idea: installing something that might not do very much good. It's disappointing to say the least, completing an installation with less than ideal results. The owner needs to be presented with all the options and their associated results, so that they are informed enough to make an educated decision on cost and performance. I've seen some large round eyeballs when giving soundproofing numbers:yes:


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## Ted White (Jul 14, 2009)

There is a natural tendency for people to assume if a highly marketed product shows up on the jobsite all will be well. Clearly that's not the case, and as Slim said, customers can easily become angry with the installer.

This is why we want to review any plans and understand any expectations before selling anything at all. It does everyone a great dis-service to blindly sell products that are not going to be installed in an optimal and satisfying fashion. This sounds like one of those situations.


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## carpentaper (Feb 28, 2009)

suite 1
____________|__door____|_______________

new drywall this side

suite 2


this is the set up .it is a wooden doorjamb and a wood framed wall probably 16" centre. so again the situation would be one layer of quiet rock only on the long wall separating the suites. nothing would be done to the bathroom because of cost. one thing i was thinking would be to add one layer of 5/8" with green glue between. i'm thinking that might be a lot more effective than the quietrock. or will it all be in vain because of the sound going through the bathroom walls and through the door.

i had a wayy better diagram with the bathroom walls using dashes but the system kept editing it all weird so i hope this is clear enough.


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## Ted White (Jul 14, 2009)

Is that a hollow core door? I doubt it's a sealed door.

Is the ceiling a dropped tile or drywall? Does the wall in question go all the way to the next floor / roof deck?


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## chris (Apr 13, 2011)

quietrock and green glue is prolly best fix. If you are putting crown molding on new drywall side,leave a gap at the angle and caulk that in with acousticalt sealant. With a good amount of insulation in wall and QR and green glue,bout as much as you can do. To maximize benefits of the quietrock use green glue as well


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## Ted White (Jul 14, 2009)

Pre-damped drywall is simply two sheets of drywall with a damping compound in between. There are 5 manufacturers of this type of board now. Not cheap, not heavy.

Adding a damping compound to an already damped board is a bit overkill. Adding damping compound to a sheet of standard 5/8" Type X is big bang for the buck.


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## carpentaper (Feb 28, 2009)

Ted White said:


> Is that a hollow core door? I doubt it's a sealed door.
> 
> Is the ceiling a dropped tile or drywall? Does the wall in question go all the way to the next floor / roof deck?


i'm assuming it is a hollow door. it is a drywall ceiling with the walls going up to ceiling. standard single family wood framed home.


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## Ted White (Jul 14, 2009)

The door will limit the performance. Spending money on the wall will almost certainly be a waste if the door isn't addressed. 

It is the lowest mass door and unsealed.


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## carpentaper (Feb 28, 2009)

if it is a hollow door i could easily replace it with a solid core door.


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## Ted White (Jul 14, 2009)

You might consider installing a steel entry door. Though it's lower in mass (lighter) than the solid core 1 3/4" interior slab, it is weatherstripped, so you're killing two birds with one stone.

Otherwise you can imagine that big gap at the bottom of the door isn't helpng...


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## carpentaper (Feb 28, 2009)

i was thinking of that. I could leave that as an option. once the wall was finished we could see how effective it is and then decide on the door before i start trimming. they might not be interested in having a steel or exterior door inside but it would help solve the weak link as you are saying.


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## Ted White (Jul 14, 2009)

Did you ever determine the stud spacing? Adding damped drywall to 16" OC wood studs isn't great, as any damped or undamped drywall needs to flex to damp the vibration. Here's the order from worst to best:

16" OC wood stud or 20 ga steel stud
16" OC 25 ga steel stud
24" OC wood stud or 20 ga steel
24" OC 25 ga steel stud

The wider stud spacing encourages a bit of flex which helps a lot, whether the drywall is damped or not. Similarly, the more flexible 25 ga steel stud flexes more than the wood or 20 ga steel, so it is also superior for isolation. Again damped or undamped drywall.

This is why virtually all soundproofing reports on walls use 24" stud spacing. You get better lab data. You will not get the same performance on a 16" OC wall.


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## carpentaper (Feb 28, 2009)

if i was a betting man i would put my money on 16 OC. 99% sure as that is just how things are done here and it was probably a spec house. nobody does anything different on a spec house.


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## carpentaper (Feb 28, 2009)

i would also bet money on it being load bearing due to its location in the house so no reframing going on.


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## chris (Apr 13, 2011)

wouldnt 16 oc give more mass?


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## Ted White (Jul 14, 2009)

Carpentaper, depending on what they want, if higher isolation was needed you could install clips & channel to the studs, then drywall. There are cheap clips under $2

Chris, more studs = more mass, true enough. Wood studs = more mass also, however in this case the slight addition of mass also stiffens the system, reducing isolation.


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