# Thoughts on sound insulation in floor?



## SimpleFix (Sep 2, 2010)

What are your thoughts on sound insulation, is it worth it? I am renovating a second floor master bedroom and bath and right now the floor is open, so I could easily put some sound insulation in the floor. There is an office under the bedroom and a kitchen under the bathroom. There are two 6" ducts supplying HVAC to the bedroom, and one 6" duct supplying the bathroom, and one large return air in the bedroom. My only concern is that it will make both rooms colder because it will not benefit from any heat coming from the rooms below.

Thanks.


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## gregzoll (Dec 25, 2006)

Roxwool would not only stop convection transmission of heat or cold, it would deaden any noise transmission, so would spray foam. If the room is properly insulated and ducted, and there is a cold air return in the hallway, the room should not be cold.


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## Windows on Wash (Aug 30, 2011)

+1

Insulating between conditioned spaces is 99% of the time for sound attenuation and is somewhat effective. You need to uncouple the framing from the finish ceiling if you really want sound mitigation but the Roxul is cheap and will help.


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## House Engineer (Feb 23, 2012)

Reducing sound transmission between two spaces is most effective when three things are done:

1. Add mass between the spaces. The 6 decibel mass law states that doubling the weight of a partition or floor reduces sound transmission between the rooms by 6 decibels. This is significant when you consider that a 10 decibel reduction sounds half as loud to the human ear.

2. Add acoustic insulation between the joists. That does not attenuate much sound as in item 1, but it dampens the airspace between the joists, which reduces the sound transmitted by vibrations traveling through the air space between the joists.

3. Provide vibration isolation between two layers of ceiling drywall. Fasten the first layer of drywall to the underside of the joists. Fasten the second layer of drywall to spring clips mounted on the underside of the first layer of drywall. This is intended to isolate the upper layer of drywall from vibrating by sound waves that contact the spring-mounted layer of drywall by sounds in the lower room.


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## Windows on Wash (Aug 30, 2011)

Vibration isolation is going to give you the most improvement in sound control.

Resilient channel with rubber isolators works well.


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## rightit (Mar 5, 2011)

To add to what's been said, the Roxul (safe and sound) will help with sound transmission at _some_ frequencies. It will do nothing, however, for impact sound (footfalls, etc.). As Windows on Wash has stated, isolation and mass is the best form of sound control.


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## manbitesfilm (Jan 24, 2012)

*What about recessed lights?*

Sorry to jack the post a bit... While on topic of floor/ceiling insulation, I'm trying to figure out the best method for combing Safe&Sound with recessed lights. There are two approaches to this as I see it:

1. Normally recessed lights need an IC rated box and those are generally pretty high, 7.5". If I have 10" joists, it leaves a tight squeeze for the 3" layer of S&S above the box. Probably doable with the extra space given by the furring or resilient channels attached to the joists... Is it useful to cover the box all around with S&S?

2. S&S is itself fire-proof, so I was thinking that if I could mount it to the underside of the floor planks (as opposed to laying it against the hanging drywall) and leave a couple of inches of space down to the light, I should be safe in terms of fire hazards WITHOUT the box. May be slightly less than the required 3", but I mean, it's Roxul, fire-"proof"... :whistling2:

So would anyone care to elaborate, either on the foolishness of the fire-risk or the inefficiency of S&S mounted directly to the underside of the floor? 

And while we're at it, can you think of the most efficient way to hold that S&S up against the underside of floor? 

Thanks in advance...

tom


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## Windows on Wash (Aug 30, 2011)

Roxul won't combust so that is not the issue.

If you insulate right up to the light and it is not an IC rated light, you run the risk of over heating the light and it tripping the overload circuit.

Making a partition out of fire rated drywall is easy and cost effective prevention.


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## manbitesfilm (Jan 24, 2012)

Thanks WOW. SO what about the second part?... Squeezing the S&S between the underside of the floor and the IC/drywall box? Still worth the time? It would effectively eliminate any airspace in that location and so I presumed lessen the dampening effect of the insulation. 

I understand that sound proofing is a 3-part effort and I should still get the other two right, but I presume the S&S should be as continuous in the cavities as possible?


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## Windows on Wash (Aug 30, 2011)

Yes.

It is cheap and well worth putting in.

:thumbsup:


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