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Old 10-19-2010, 03:39 PM   #1
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Insulation - 2 questions

In the process of building a 2 story home and I have two questions in regards to insulation.

1) I plan to insulate interior walls surrounding all bathrooms, for sound reduction purposes. The walls are 2x4, and my question is should I use Kraft faced R-13 insulation with the paper towards the bathroom side or should I use unfaced batts in these interior walls? I know to use Kraft faced batts on the exterior walls, just wasn't sure about the interior walls. My guess is to use unfaced batts to prevent moisture from being trapped within the walls? Any advice is welcomed.

2) Upstairs I have 1100 sq ft of living space, with a game room, guest bedroom, and a bathroom. Downstairs I have approximately 1700 sq ft of space with three bedrooms, two baths, etc. The joists between floors are 2x10. From what I've read I don't have to insulate this area, but it may help with soundproofing? The added cost of insulation is not an issue if this will help conserve energy and reduce noise transmission from one floor to the next. My question is, should I insulate between the two floors? And if so, I'm assuming I should use unfaced batts?

First time posting, thanks for any help or opinions.


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Old 10-19-2010, 07:15 PM   #2
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If you are looking to soundproof, check into the products specifically designed for it. typical fiberglass insulation is better than nothing, but not by much.


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Old 10-19-2010, 09:42 PM   #3
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It makes no sense to insulate a wall or floor separating two spaces inside the exterior insulated envelope.

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Old 10-20-2010, 07:33 AM   #4
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Fiberglass insulation is not the ideal material for sound absorption, but is still much better than hollow cavities. Since you are not insulating for thermal correction, you can pack the fiberglass much more densely than an exterior wall. Denser packed fiberglass is a better sound absorber. Seal off all penetrations into the cavities first. Avoid light switches and receptacles in the soundproofed wall if possible. If unavoidable, seal all openings into the boxes and seal the boxes to the drywall. For the floor spaces, you might want to consider blown in cellulose. It could be a lot easier than tearing out ceilings. In any case, you need make sure every void is filled. Tight into corners, tops and bottoms. As far as facing, since your temperature will be equal on both sides of the wall, the vapor barrier is a non-issue. If temperatures are equal on both sides of the insulation, there is no vapor pressure differential and moisture will not travel. Since the paper facer is at room temperature, it will be above dew point and moisture can't condense on it.
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Old 10-20-2010, 08:04 AM   #5
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There are 'Z' shaped pieces of metal that are called 'sound bar' to attach your ceiling drywall to that reduce sound transfer.
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Old 10-21-2010, 02:14 PM   #6
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Thanks to everyone that responded.

The reason I asked about insulating the joists between floors was because I had read somewhere that heat may be lost to the upstairs in the winter and the opposite in the summer. The sound reduction aspect would be a bonus as well. Also I figured it would be better to insulate this space now, as opposed to finishing the drywall then having to drill holes and blow in cellulose down the road. I'm going to go ahead and insulate this space now with fiberglass batts, since the pros outweigh the cons from what I understand. However if anyone feels that insulating between floors will cause problems, I'd sure like to hear their arguments/opinions. I'm building this house for myself, so I'm trying to do things the right way when possible.

Also I'll definitely be insulatting all the interior walls that surround the bathrooms again for nothing else but the potential sound reduction benefits.
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Old 10-27-2010, 03:19 PM   #7
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There is a fair amount of good ol urban legend expressed in this thread. No one is at fault, as this is commonly spread across the internet.

When insulating a hollow cavity for soundproofing purposes, especially for low frequency (bass) soundproofing, nothing is better than the cheapest fiberglass you buy at Home Depot, etc. This insulation cannot be packed, or you risk conduction of the vibration by the insuloation itself. There is simply no advantage to installing anything that says "acoustic."

For ceilings, just use standard R19 fiberglass. For walls, use R13. There's a great deal of raw lab data online that supports this.

Additionally, foam is excellent for thermal purposes, but terrible for acoustic. It's just too dense.


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