Wall sound insulation

[slogical]

Hi,

I live in an ex-local authority semi-detached house with a solid 9 inch wall separating the two houses. When renovating my property I dry lined the dividing wall in the living room leaving a 25mm air gap between the wall and a single layer of 12.5 mm plasterboard.

We have new neighbours who like to listen to their TV quite loud(!) so I have been looking at improving the sound insulation. I had assumed that filling the 25mm air gap would improve the sound insulation, as a trial I filled the gap with vermiculite but this seems to have increased the amount of sound being transmitted through the wall, does this make sense to anyone? I had assumed that filling the air gap with a reasonably sound absorbent material would help, am I wrong? The plasterboard is fixed to the dividng wall using 38mmx25mm battens at 400mm centres.

Thanks in advance

 

[Blagard]

I would have thought what you did would improve the situation to, so I decided to check the what the Web has to say and found Wiki was good with a detailed explanation.

http://en.wikipedia.org/wiki/Sound_transmission_class

Why what you did has not worked seems strange to me. It is as if the vermiculite is aiding structure bourne sound transmission by introducing contact where previously you had an element of de-coupling as wiki would call it.

Certainly not what I would expect from such a material.

In Travel lodge construction using dryling wall construction the division wall between rooms was actually two walls with a gap betweem them and both sides double layers of wallboard, plus insulation between the studs. so there they introduced mass, de-coupling and insulating material, the latter which did very little to help other than keep one room warmer than it's unheated neighbour!

 

[Deluks]

The insulation does make a difference, missing out the inso to save a few quid can make the difference between a win and a lose.

Slog, as suggested, vermiculite would transmit low freq. using a fibre based insulation such as rockwool etc. would have improved things slightly. I say slightly because 25mm isn't much of an airgap, and you probably fixed the plasterboard onto battens which are fixed onto the wall, this is your weak point.

Might have to tear it all down and start again, if you can bear to do so?

 

[slogical]

Thanks for the replies.

Not sure I can bear to rip it all down but I agree with your explanations as it was a very small air gap to start with and the plasterboard is fixed to battens - it wasn't originally planned for acoustic insulation. It also does seem to be low frequency sound that is being transmitted since filling the wall. I think I will remove the vermiculite.

The dividing wall is made up of 1.4m alcoves either side of a 1m chimney, the current plan is to build storage into the alcoves. The storage will be attached to the chimney and side walls but not to the dividing wall with 1 inch air gap and 1 inch acoustic insulation between the dividing wall and the cupboard back then a 10 inch cupboard with solid doors. Hopefully this should make enough of a difference, even if it doesn't we desperately need the storage!!

 

[Deluks]

Make it two inch gap, 50mm rockwool in there, make the 'back of the cupboard' a layer of ply topped with a layer of plasterboard, then build your carcasses and doors.

 

[Blagard]

My Mothers house had one very weak sound insulation point. -The fireplace. It was just a half brick thickness between the semi next door. It had not been helped by the removal of traditional firebacks when gas fires were fitted. Both semi's were done and I am convinced if I could have looked hard enough I would find holes in that area. - No problem now as that was decades ago, but you might want to check that area as well.