Sound Transmission class | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Ronnie natal Posted: Jun 08, 2009 10:19 AM	Sound Transmission class Can you please tell me if the sound tranmission class of open cell foam is 51 in a 2x4 assemly @ 2 1/2" thick. What would it be in a 2x6 wall @ 4 1/2" thick?
mason Posted: Jun 08, 2009 10:33 AM	You would need to get that information from your supplier as the foam's specific sound transmission properties may vary from foam to foam. Here is an example of the sound transmission testing on Icynene's foam. www.icynene.com/assets/documents/pdfs/Resources/Building-Science/STCTesting.pdf
mason Posted: Jun 08, 2009 10:41 AM	To amplify on your question. I went to a few websites and noticed that most open cell foams have a STC of from 37 to 39 at 3.5 inches and a Noise Reduction Coefficient of around .75. I am sure the STC is not an arithmetical progression but I would expect the STC would be slightly less at 4.5 inches than at 3.5 inches. I am not aware of any testing at that specific thickness. Any suppliers out there with more detailed information?
Ronnie natal Posted: Jun 08, 2009 11:17 AM	I am in need of a specific STC # for a 2x6 wall, I have called 5 manufacturers and I had 2 tell me that theoretically I could double the STC # if I double the thickness. Then 2 are calling me back, the other one says; it will improve as you said Mason, but to what educated degree can I state that it does improve? I'm trying to make an accoustical engineer happy here. lol
jimcoler I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs. I've expanded my knowledge into t Posted: Jun 08, 2009 07:14 PM	Be careful! Don't fill the cavities full for sound transmission. A full cavity will actually allow for more sound transmission throught foam and wall than with an air space. The irregular surface of many of the foams and the soft 1/2lb foams help to reduce the sound transmission too. Good luck.
Ronnie natal Posted: Jun 09, 2009 04:44 PM	After 8 hours of STC research, I feel preety good about what knowledge I've picked up. I still don't know why they over built these walls, 2 layers of 5/8"gyp, 2x4 with batt, 8" cmu wall grout filled then another 2x4 wall with 3 layers of 5/8" gyp also with batt, I'm pretty sure a 2x6 wall with 4 1/2" of open cell with sound board on either side and one layer of 5/8" will do, but I'm still no expert. I also can't find a single diagram of a wall assembly showing foam and listing their STC #. I believe it would benefit all of us if all of the foam manufacturers got together and split the cost of running the tests necessary to help us sell this product with the hard facts to back it up.
Shawn Faherty Posted: Jul 09, 2010 05:59 AM	Interesting idea about having some air in between the wall and foam. I was thinking of adding strapping to all my studs and joists after the foam is applied. This would create a nice cushion of air (about 1/2") and more area for the drywall to be drilled into (plaster guys like to work this way, makes for super flat walls). The other reason I was thinking strapping would help (haven't searched this in the forum yet, so this is my first writing about it): The major problem with foam is that the wood studs still act as a thermal sponge. I wanted to add a foil to the inside or outside of them to break this transfusion and then add the strapping. Has this been done? Should I have them put in steel studs where ever they can and increase the spacing to 24" while they are at it (for less studs because the foam is adding strength anyway)?
Cory Boehs Posted: Jul 10, 2010 07:07 PM	Try Demilec's website. I believe they have diagrams and STC ratings.

Author

Comments

Ronnie natal

Posted: Jun 08, 2009 10:19 AM

Sound Transmission class

Can you please tell me if the sound tranmission class of open cell foam is 51 in a 2x4 assemly @ 2 1/2" thick.
What would it be in a 2x6 wall @ 4 1/2" thick?

mason

Posted: Jun 08, 2009 10:33 AM

You would need to get that information from your supplier as the foam's specific sound transmission properties may vary from foam to foam. Here is an example of the sound transmission testing on Icynene's foam.

www.icynene.com/assets/documents/pdfs/Resources/Building-Science/STCTesting.pdf

mason

Posted: Jun 08, 2009 10:41 AM

To amplify on your question. I went to a few websites and noticed that most open cell foams have a STC of from 37 to 39 at 3.5 inches and a Noise Reduction Coefficient of around .75.

I am sure the STC is not an arithmetical progression but I would expect the STC would be slightly less at 4.5 inches than at 3.5 inches. I am not aware of any testing at that specific thickness.

Any suppliers out there with more detailed information?

Ronnie natal

Posted: Jun 08, 2009 11:17 AM

I am in need of a specific STC # for a 2x6 wall, I have called 5 manufacturers and I had 2 tell me that theoretically I could double the STC # if I double the thickness. Then 2 are calling me back, the other one says; it will improve as you said Mason, but to what educated degree can I state that it does improve? I'm trying to make an accoustical engineer happy here. lol

jimcoler

I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs.

I've expanded my knowledge into t

Posted: Jun 08, 2009 07:14 PM

Be careful! Don't fill the cavities full for sound transmission. A full cavity will actually allow for more sound transmission throught foam and wall than with an air space. The irregular surface of many of the foams and the soft 1/2lb foams help to reduce the sound transmission too.
Good luck.

Ronnie natal

Posted: Jun 09, 2009 04:44 PM

After 8 hours of STC research, I feel preety good about what knowledge I've picked up. I still don't know why they over built these walls, 2 layers of 5/8"gyp, 2x4 with batt, 8" cmu wall grout filled then another 2x4 wall with 3 layers of 5/8" gyp also with batt, I'm pretty sure a 2x6 wall with 4 1/2" of open cell with sound board on either side and one layer of 5/8" will do, but I'm still no expert. I also can't find a single diagram of a wall assembly showing foam and listing their STC #. I believe it would benefit all of us if all of the foam manufacturers got together and split the cost of running the tests necessary to help us sell this product with the hard facts to back it up.

Shawn Faherty

Posted: Jul 09, 2010 05:59 AM

Interesting idea about having some air in between the wall and foam.

I was thinking of adding strapping to all my studs and joists after the foam is applied. This would create a nice cushion of air (about 1/2") and more area for the drywall to be drilled into (plaster guys like to work this way, makes for super flat walls).

The other reason I was thinking strapping would help (haven't searched this in the forum yet, so this is my first writing about it):
The major problem with foam is that the wood studs still act as a thermal sponge. I wanted to add a foil to the inside or outside of them to break this transfusion and then add the strapping.

Has this been done? Should I have them put in steel studs where ever they can and increase the spacing to 24" while they are at it (for less studs because the foam is adding strength anyway)?

Cory Boehs

Posted: Jul 10, 2010 07:07 PM

Try Demilec's website. I believe they have diagrams and STC ratings.

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