Author Topic: Insulation  (Read 5528 times)

whatismisophonia

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Insulation
« on: February 09, 2012, 07:42:48 AM »
I thought i had asked this question a while back, but i cant seem to find it under my posts any where...  Im wondering If cotton bats are better over all than fiberglass or rockwool.  Ive heard it said that most types of insulation have minimal differences in terms of noise control. Do they treat the cotton to make it repellent to insects and flame? 

whatismisophonia

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Re: Insulation
« Reply #1 on: February 09, 2012, 01:10:50 PM »
scratch the insects and flame part; found out about the chemical treatment.  Have stayed up all night (again ugh... when will i learn to quit that) and can find only minimal if any differences in the insulative and acoustical performances in various batt insulation types.  Wandering if there is anything special about cotton that makes it worth choosing over mineral wool's superior fire resistence (or even plain jane fiberglass, for that matter). Seems expensive.

Randy S

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Re: Insulation
« Reply #2 on: February 09, 2012, 01:37:07 PM »
This is where field experience trumps lab reports, all I can say is go grab a few bats of each make a couple panels and see for yourself.... I have seen first hand reductions of up to 35db of reflection for a 14' span in the field.
Not saying mineral wool is bad, actually that is a great product also....
we find ourselves back to cost vs. reduction.
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whatismisophonia

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Re: Insulation
« Reply #3 on: February 10, 2012, 02:44:56 AM »
reflected? brooding... ive heard that the cotton, once compressed, has a difficult time fluffing back out.  In what manner do these batts flex and conform compared to fiberglass? parhaps they add rigidity(or simply flex differently) without sacrificing air pockets.  Parhaps the matterial isnt as springy, so its more of a damper(its organic nature makes it behave in a somewhat viscous, time-delayed manner?) since, when you say reflection, it makes me think that the insulation is effecting the wall leafs differently than other insulation.  That is, of course, considering that it's even touching the source wall; which may not be the case since you guys like seem to like to use mass loaded vinyl alot.  There is also the fact that the company that makes your cotton batts makes them a little oversized to compress better into the wall cavity; perhaps they are working to dampen the structual members?

Randy S

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Re: Insulation
« Reply #4 on: February 10, 2012, 03:53:11 AM »
Hahaha.. well you are starting down the rabbit hole....here is where all the details cause greater control or reductions..
Yes, making the bats to commercial structure widths is the best to use...the detail is to make sure the cavity is completely filled..No Gaps at all....
you dont want rigidity you want the best of both worlds... your trying to isolate the magic wand...way to many variables for a single product to address....
but
your thinking as if the project I mentioned was a wall cavity installation.... that would have been a lessor value as apposed to full exposure to the sound.
It was an elementary school open cafeteria... base reading 87 db ....14' metal ceiling / reflection reading 102db!  after treatment reflection came back at 65db-67db....in other words you could now talk across the table without yelling. :)
 
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whatismisophonia

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Re: Insulation
« Reply #5 on: February 10, 2012, 05:01:08 AM »
-_- ........so are we all of the sudden talking about acoustic panels now? Different then what i was wanting to talk about.  Oh well.

ArminRU

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Re: Insulation
« Reply #6 on: February 10, 2012, 05:02:46 AM »
Hahaha.. well you are starting down the rabbit hole....here is where all the details cause greater control or reductions..
Yes, making the bats to commercial structure widths is the best to use...the detail is to make sure the cavity is completely filled..No Gaps at all....
you dont want rigidity you want the best of both worlds... your trying to isolate the magic wand...way to many variables for a single product to address....
but
your thinking as if the project I mentioned was a wall cavity installation.... that would have been a lessor value as apposed to full exposure to the sound.
It was an elementary school open cafeteria... base reading 87 db ....14' metal ceiling / reflection reading 102db!  after treatment reflection came back at 65db-67db....in other words you could now talk across the table without yelling. :)

When you say the cavity should be completely filled, do you mean side to side only.....or top and bottom as well?  I ask because most rock wool and cotton batts come anywhere from 3"-10".  Usually this is not thick enough to fill the entire joist cavity top to bottom....side to side isnt a however since they are precut perfectly.

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Re: Insulation
« Reply #7 on: February 10, 2012, 04:05:33 PM »
side to side for the fill and normally we like to use 5 1/2" thick R19..

-_- ........so are we all of the sudden talking about acoustic panels now? Different then what i was wanting to talk about.  Oh well.

You have to understand when a material has reached its diminishing point of return...and trying to tweak it any further is not worth the effort when you can address the next issue with a different principle...
Insulation in a cavity is mostly absorption but it is not directly exposed to sound so the true NRC is not the same as the results produced by ASTM 423 test method and if you can also gain some value of STC ...great! otherwise I wouldnt expect more than that.
Materials perform differently based on the way are used...I idea is to get the best performance it can deliver and move to the next material.

Randy Sieg

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ArminRU

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Re: Insulation
« Reply #8 on: February 11, 2012, 12:24:52 AM »
side to side for the fill and normally we like to use 5 1/2" thick R19..

You have to understand when a material has reached its diminishing point of return...and trying to tweak it any further is not worth the effort when you can address the next issue with a different principle...
Insulation in a cavity is mostly absorption but it is not directly exposed to sound so the true NRC is not the same as the results produced by ASTM 423 test method and if you can also gain some value of STC ...great! otherwise I wouldnt expect more than that.
Materials perform differently based on the way are used...I idea is to get the best performance it can deliver and move to the next material.

So are you saying in a insulation application (i.e. insulation stuffed between joists in between two walls, is fiberglass/rock woll/cotton any better than the other.....or maybe just slightly better than the other.  Not sure if I'm following.

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Re: Insulation
« Reply #9 on: February 11, 2012, 01:47:33 AM »
Sorry for causing some confusion...

Cotton fiber has a great NRC and a good density therefore a good STC contribution to the assembly. Our Choice.
Mineral wool has a good NRC and a decent density.

So these 2 would be top choice

Fiberglass has ok NRC and little STC value.

Blown in cellulose is better than nothing in the cavity, sorry but I dont believe the testing data because its basically recycled paper...which could prevent standing waves in the cavity if it doesn't leave a large gap at the top when settled. Use this when the cavity is empty and you dont want to remove the drywall for bat installation.

expansion foams are really only thermal value and could cause increase in sound transmission.

everyone has opinions but this is what we see in the field and feed back from clients. Also remember even though it is insulation and normally thought of for thermal applications this IS NOT the principle we are looking for when used in sound control assemblies.
 
Randy Sieg

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

 

anything