Insulating for sound on neighbour's wall

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I'm looking to reduce noise transfer between us and our semi detached neighbours... I know there's "better" ways to insulate for sound but the first option I looked at includes leaving a 50mm void & means losing 130mm of living room.

Instead this is our current plan on entirety of our shared wall is this, losing only 55mm:

  1. Screw 25x38 batten to the wall
  2. 5mm acoustic tape to battens
  3. 50mm Rock wool sound slab (couldn't find 25mm so planning to compact it down) between the battens (slabs are 600mm wide)
  4. Double board with 12.5mm knauff acoustic board
  5. Skim

Any thoughts on how effective this will be and any simple /easy ways to improve the outcome please?
 
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What sort of noise are you trying to eliminate- airborne (conversation or tv/music at medium and high frequencies) or conducted (footsteps and doorslams)?

In a semi it is quite possible that floor and ceiling joists are linked to next door and there may be gaps where the timbers pass through walls. Check which way your joists are running.

If you are getting noise through the party wall your plan won't improve things that much. The acoustic properties of the wool will be degraded by compressing it. Your 'acoustic tape' is going to do nothing if the plasterboards are screwed through it. The mass of double acoustic boards will help but they'll perform much better if you can decouple them from the noise-bearing structure.
 
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Consider resilient bars.

I don’t think the idea of compressing acoustic slab to half thickness is likely to work.
 
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Thanks for the replies. it's as much for noise getting out from us to the neighbours as it is their noise to us - apart from anything else, we want to be able to watch a film without having to worry too much that we might be annoying them.

Joists run parallel to the party wall so that's unlikely to be causing any transfer, although the closest joist is barely an inch from the wall. so who knows what that's obscuring in the way of gappy brickwork!

it's a 50's ex council so prettily solidly built. It's occasional loud voices / shouting and door slams that mostly come through. there's also infrequent socket and light-switch clicks hangar scrapes when it's very quiet at night, but i can live with that.

I realise we would be far better to build a decoupled wall and this was my original plan but I don't feel i can justify the loss of space from doing this.

I did wonder if the acoustic tape would serve any purpose for use in this way. My original plan was to run it around the perimeter (ceiling, floor and side walls) of the "floating" decoupled stud wall. If it's not going to make much difference applying to the battens before double boarding, I may dispense with with it all together.

good points have been made about compressing the sound slab insulation, so here's the next question - what's better - 50mm insulation compressed to 25mm, or me attempting to take 50mm and split in half taking it down to 25mm depth?
 

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