Interior Wall Insulation for Soundproofing Thoughts


Old 01-05-14, 08:10 AM
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Interior Wall Insulation for Soundproofing Thoughts

Our upstairs bedrooms are all essentially 4 bedrooms and two bathrooms all interconnected in a "U" shape around the hallway. We can all hear each other snore, play music on their phone, go tinkle in the bathroom, etc.

My wife suggested we just rent a machine and blow in some cellulose insulation between the key walls and it should dampen the sound. I'm OK with that as it probably isn't much more than putting some small 2" holes in the top of the wall and blowing it in and plugging the holes, which is certainly in my DIY range. I'm just not sure if I'm missing any looming issues that would make this a bad idea? Are the holes impossible to cleanly patch without a pro drywaller if in an open wall in a room that gets hit by sunlight? Is it better to just use panels if we're moving in 2-3 years?

Anyone have any experience and can guide me of any pitfalls or do's and don't here?


Jeff in PDX
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Old 01-05-14, 10:31 AM
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The walls on each side are probably sheetrock screwed into the the same possibly metal frame, so that transmits sound.

Blow in insulation settles leaving a void on top that could allow sound to pass.

Holes can be patched, but repainting is hard to match new and worn paint exactly.

If you have forced air ducts they transmit sound.

If the ceiling or floor is uninsulated


So there are many paths sound might be traveling.
Old 01-05-14, 10:52 AM
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I'd have to say...I doubt there will be that much improvement for the work and expense involved. The main thing to dampen sound is mass...and insulation doesn't have much.

I'm not sure what "better to just use panels..." means?
Old 01-05-14, 11:02 AM
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Thanks. I was referring to some of the after-market stuff you see for acoustic insulation. Such as this product from Lowes:
Shop 1/4-in x 48-in x 8-ft R0.3 Acoustic Insulation at

Also, you see some of those foam panels you can put around a room to deaden the sound (assuming they essentially absorb sound prior to it getting to the wall and thus deadening the amount of sound that hits that drywall, which likely is acting much like a drum when it doesn't have insulation.

I've read some reviews in the meanwhile that talk about difference blowing in insulation can make just in lessening that "drum effect" that can be created with drywall and nothing between it. But it does seem to me that this would almost have to be an epidemic problem since I'm guessing many houses get built with no insulation between two adjoining rooms, so I'm not sure why we seem to have such "thin walls" and can hear everything as where nobody else has that problem. Strange.
Old 01-05-14, 11:08 AM
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Old 01-05-14, 11:37 AM
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Filling the wall cavity will cellulose will definitely be better than nothing, and it will reduce the hollow sound coming through walls. But it won't dampen noise coming from your hollow core doors, or under the gaps beneath your doors. it won't dampen any sound that is coming through your heat ducts or cold air returns. And as mentioned it won't dampen any sound that's being transmitted directly through the framing.

But I think you would definitely notice a difference. Whether or not that difference will be enough to make it worth your while is another matter.
Old 01-05-14, 11:48 AM
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Good info. Thanks. Since we have solid core doors and carpet that drags pretty tight, I think we're OK there, but good points. Not sure about the ducts, but I definitely hadn't thought of the fact that ducts are right there running in a line along the ceiling throughout each room and would be open conduits of sound to move. Definitely something to think through for weighing that time/money. Thanks again!
Old 01-05-14, 12:44 PM
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I think it provide some improvement, but not much. You will get a lot of sound bypassing the wall by going under and over it. My brother has a bedroom that shares a wall with a bathroom. The toilet and shower happen to be on that wall. They applied quiet-rock to the wall in an attempt to get things quieter and it just didn't do as well as hoped.

If you are only going to be there for 3 more years, it might not be worth all the work involved. Blowing in cellulose is going to be a huge mess inside. If you planned to be there for several decades, I would say go for it and chase down every by pass as you work.

EDIT: I wanted to add that if you decide to try something to get a sound meter to measure before and after. Make sure you replicate the same scenario for your testing. Maybe the same radio with the same song set to the same volume, etc etc. You can also get a sound meter app for your smart phone. Not sure how reliable they are, though.

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