atilla137

I am finishing my basement and I am insulating the ceiling and interior walls with Roxul Safe N Sound. When I insulated the ceiling I pushed the insulation up against the underside of the floor. Will the insulation eventually sag and fall onto the drywall? Should I use something to support it and if so, what? My house is a semi-detached and I want to insulate the common concrete wall that separates the two basements. Is this ok? A friend told me a contractor told him not to insulate this wall because of moisture concerns. If I insulate the common wall should I use vapor barrier as well?
Thanks in advance for any suggestions

concretemasonry

Why do you want to insulate the common wall? Is the other side too hot or cold?

Insulation would do nothing to help with sound.

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Colonel Hogan

FOr foam panel or any type of battr/roll insulation, you can use Simpson Strong-Tie insulation supports. These are thin spring steel rods with sharp ends that you arch into place under the insulation; the sharp ends are poked into the the sides of the joists holding the insulation in place. They come in different lengths, just match the length to your joist spacing.

atilla137

Insulation specifically designed to block sound will do nothing to help with sound??? That doesn't make ANY sense!.

atilla137

Exactly what I needed. Thank You

concretemasonry

atilla 137 -

What I meant about sound was that if you have a concrete common or party wall, adding lightweight insulation will do next to nothing to decrease the sound transmission through the wall. The sound transmission depends on the wall weight.

Even resiliant channels or sheet lead would have a very minor reduction in sound since you alread have a 55+ db rated wall. You might add 1 db to the rating at best, since it is very difficult and costly to improve on a solid wall.

If you are building a wood frame wall in front of the concrete, you can add insulation between the studs with no problem, but it would really be a waste of money. Your concrete wall would have a 55+db rating and a wood wall with insulation might be 40db, but the resulting total would be about 56db since you cannot add db's to get a total db rating. The db ratings are a logarithmic value they cannot be added.

Once you are in the area of 55 db, it is very difficult to increase the db rating. As an example, going from one 8" wall to 2 - 8" walls (one one 16" wall), the db rating would only go up to about 57 or 58 db.

If you have a unique problem. you might want to take a look at the area above the concrete wall. This is an area susceptable to sound transmission and the transmission of vibrations from the adjacent portion of the wood structure.

If you are talking about a wood stud or a steel stud (worse yet), then resiliant clips or channels for the sheet rock are the way to go.

I would not add a vapor barrier to the wall since both sides of the common wall are conditioned or semi-conditioned spaces and will have the same conditions on both sides. Tradition says put the vapor barrier on the warm side - what if your neigbor has his heat higher than yours? You certainly do not want a wall with a vapor barrier on both sides.

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atilla137

Thank You
I think that you are right about the sound coming through the wood above the common wall. I have insulated the ceiling and the wood above the concrete wall. You obviously know your 'crete!
Thanks Again
Atilla137