Author Topic: Floor Joist Cavity Sound Dampening Suggestions  (Read 11093 times)

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Floor Joist Cavity Sound Dampening Suggestions
« on: November 09, 2011, 01:55:10 AM »
I have a two story condo that shares a common wall with a single story (vaulted ceiling) unit. I am going to be attempting some soundproofing on the common wall (more about that later) which is a staggered double stud wall. My question is regarding the floor joist cavity area that abuts the common wall.

My floor joist run perpendicular or 90 degrees to the common wall and the unit next to my two story is a one story with vaulted ceiling the area is at the very end of the floor joist inside the cavity on the common wall it self. I would like some ideas on what might be a good way to reduce the noise transmission in the area between the 12"-joists where the floor meets the wall


I can access that area buy cutting an opening in the drywall ceiling from below or from the floor above.

Randy S

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #1 on: November 09, 2011, 04:46:07 PM »
If your trying to reduce impact and footfall from entering the ceiling next to you, than the only thing that will work is to float your floor above...reduce the impact at the source...once the impact is in the subfloor your not going to reduce it unless you float your neighbors ceiling.

You can insulate the cavity but that will only help on the airborne remittance of impact noise...it will not reduce the structural remittance of the drywall screwed into their ceiling.

You must break the connection and your not going to be able to do this in the framing.

feel free to contact me directly if you would like to discuss in more detail.

Randy S.
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Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #2 on: November 09, 2011, 09:05:38 PM »
Thanks not worried about footfall noise and the wall is staggered so I was considering drywall and Greenglue in the joist cavity on the common wall only and then some insulation. I realize the sound can travel through the structure but if it would reduce the noise overall I would do as described or maybe blow in some insulation in that area instead.

I have applied a 5/8" layer of drywall and GG in the Master bathroom and was told it could take up to 30 days for the GG to become totally effective so I am waiting to see the results and evaluate what to do in the Master Bedroom from that.

Space was limited in the bathroom so only one layer of drywall was possible due the toilet drain but I think I am going to need to address the flanking noise area also.

Randy S

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #3 on: November 10, 2011, 04:22:38 PM »
Then in that case you are the right track, always fill cavities even if you can only do blown in...its better than having an empty cavity.
Green Glue will take a full 30 days to reach optimal performance, however look at green glue dampening compound like you putting your hand on a speaker while its playing....the speaker is still playing just not the same way....So if you want to "Beef up" the system you can add a layer of #1 Mass loaded vinyl w/psa directly to the existing drywall followed by new drywall with green glue sandwiched in between.
This will greatly improve the STC rating of your wall.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

Randy S

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #4 on: November 10, 2011, 04:22:49 PM »
Also there a couple of tips for applying green glue.
1) Do not leave a 2" border of drywall that is not covered with green glue... a 1/2" border is enough...if you need to clean it off your hands use Avon so soft.
2) A lot of methods of application are being thrown out there, like big squiggly lines or tic tac toe pattern etc etc..understand that when you make the sandwich you want the void sizes to be no bigger than a quarter so apply it like silly string all over the sheet 1/4" bead so that you get maximum coverage...you dont want 4" -8" void sizes on the wall.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #5 on: November 10, 2011, 05:10:37 PM »
Great info only wish I had found this site before I hung the bathroom drywall. I didn't leave a 2" border rather I applied it to the existing drywall instead but I also didn't make as fine of a pattern you describe but no voids of 4" either.


Would 2 layers of green glue & 2 layers of 5/8" drywall be better or as affective than the MLV & one layer of drywall?

Just to clarify I can apply the green glue directly to the MLV?

And regarding the acoustic sealant 1/4" border gap around the drywall, is it ok to tape as normal over that area?

Thanks again ...




 


Randy S

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #6 on: November 10, 2011, 08:26:01 PM »
good deal on your green glue, in the future it is easier to apply it to the back of the new sheet your installing.

a layer of MLV with green glue is better for airborne noise than the double GG w/ drywall

You attach MLV to existing wall then apply green glue to back of new drywall then screw into wall.

you do not need the gap around perimeter because you are not floating...so you can mud and tape corners.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #7 on: November 10, 2011, 10:25:00 PM »
You the man Randy S ...

I applied the GG to the existing drywall due to the bathroom size I was unable to lay the drywall flat on the floor so it seemed better to do it that way and not have to deal with the mess if I had applied the glue all the way up to the edges. But in the Master bedroom I'll have more room to work it properly.

To keep my options open from good to best what are some types of insulation to use in the floor joist cavity?
The blown in would definitely be the easiest in this case and I may go that route if the wall is reducing the sound to a decent level.

Thanks ...




Randy S

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #8 on: November 10, 2011, 10:55:14 PM »
Our view points on insulation:

1) cotton fiber insulation (recycled blue jeans)
2) mineral wool

better than nothing in the cavity

3)fiberglass
4) blown in

And trust me, I have had clients see a value of noise reduction in all the types of insulation it really comes down to how much vs. cost.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #9 on: November 11, 2011, 01:22:52 AM »
Good to know.


Thank you very much for all your help ...

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #10 on: December 16, 2011, 08:16:00 PM »
It's been over 30 days and the intial improvement I saw is all I achieved with the greenglue. It is all I am going to do in the bathroom for now with the limited space,
 

The MLV and RC are more than Iam wanting to spend at this time.

So I am thinking about using a layer of styrofoam sheeting on top of the existing drywall (working on the Master Room now) then soundboard and finish with 5/8" layer of drywall. My thinking is the styrofoam would not transfer vibration readily to the soundboard which would then dampen the sound and also make for three differrent layers of different weight materials and properties.


Any thoughts?

Randy S

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #11 on: December 16, 2011, 10:05:09 PM »
I am not surprised, as I mentioned in an earlier post Green glue is a dampening compound not a mass value...

Here lies the problem, look at the screws like tuning forks and the structure like the amplifier finally the drywall as the speaker....there is the fastest path through the system...

if you want to see far better results in the bedroom I advise you to decouple at the very least...styrofoam will not help....well for building a cooler yes but not for soundproofing.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #12 on: December 16, 2011, 11:28:22 PM »
Thanks Randy the common wall is a staggered double 2x4 so is it not already decoupled?



Randy S

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Re: Floor Joist Cavity Sound Dampening Suggestions
« Reply #13 on: December 20, 2011, 08:42:04 PM »
Well, some people view that as a decoupled system...however, when you look at the speed if vibration(sound) through wood it is 12x faster than airborne sound (around 13,000 fps) is it really decoupled...... I say no, it could be better.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

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Re: Floor Joist Cavity Sound Dampening Seggestions
« Reply #14 on: January 06, 2012, 12:33:02 AM »
I ended up working on the second upstairs bedroom since it is the quitest I felt it would have the best chance for success.

I used a layer of styrofoam sheeting on top of the existing drywall  then a layer of soundboard sheeting, another layer of styrofoam and finish layer of 5/8" drywall.

It has been several days now and I would estimate a noise reduction of 50% and I am fairly pleased with the results and cost.

I will evaluate more and post some observations later.