This mainly affects:
Part B Fire Safety
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1640,en.pdf
Part E Sound
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1646,en.pdf and
Part L Conservation of Fuel and Energy
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,20322,en.pdf
of the Building Regulations.
Other regulations will be affected
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+1 what Towger has posted regarding thermal insulation (BTW, good links Towger - thanks)
In general, you don't install thermal insulation to party walls - you install it to external walls, i.e. the front and rear walls in a terrace.
The party walls are discounted in assessing thermal performance because these are not exposed to the environment and are deemed to be heated from the other side.
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Acoustic performance of walls require that masonry walls be solid and without holes or penetrations with all the joints, both bedding and perpend joints [horizontal and perpendicular], between block to be laid "full bed" of mortar.
The solidity of the wall is affected in two ways; -
1. Some blockies/brickies lay two lines of mortar either side of the blocks/bricks with just a "lick" up the vertical joint. This is sharp practice and designed for speed not integrity as it compromises a wall in terms of its strength, fire resistance and ability to prevent sound transmission. At its worst, you can see holes straight through the wall.
2. Hollow blocks and bricks with honeycombs in them are less massive and less resistant to certain types of sound.
Both of these shortcomings can be addressed by a good three-coat render, scratch, scud and finish - the intention to is to seal all the joints and the wall as a whole.
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Special attention should be paid to party walls in the attic - sometimes these don't exist! In older properties the attics can be continuous along a terrace. This is not good practice for either fire or sound resistance and the party walls and eaves barriers should be installed in accordance with Diagram 13 Page 81 in Technical Guidance Document B, the URL of which is given above.
The Party walls should be inspected for their full height and all holes, penetrations, and building in noted as all can contribute to sound transmission and a lack of fire resistance.
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Pay particular attention to; -
a) the joint between the party wall and the front and rear walls - sometimes the joint can fail and leave a through-joint, which means that the outer terrace walling is "floating" and is effectively unrestrained or unbuttressed by the party wall cross wall.
b) the floor and ceiling levels, where built in timbers can contribute to risk in a fire emergency and can result in unsealed penetrations transmitting sound - the members in the wall can also transmit impact noise through from one side to another.
Remedies exist for mitigate and/or remove all these problems.
For example, structural timbers can be given alternative means of support and the ends cut back, the ends removed from the walls and replaced by blockwork.
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Where the works to the walls are completed per the comments above and there are still difficulties you might need to install additional sound proofing details.
1. On the surface of the wall you can install quilted material between studs and face the stud with acoustic board to absorb airborne sound.
2. The floor boards can be taken up and an absorbent detail installed to both the top of joists and floor perimeter to reduce sound transmission.
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You can see from all this that the neighbour's assistance in dealing with sound caused by him is important because this deals with it at source.
Failing this all you can do is deal with effects of his sound on the party wall surface affecting you.
On word of warning:
This is specialist design and building work.
The principles of what is being attempted must be well understood.
It is imperative to involve both an architect and an engineer as well as an experienced builder to deal with these problems.
Both neighbours either side of the affected wall should work together to achieve the desired result, including temporary propping.
Failure to retain professionals could result in structural instability of party walls, removal of support, cracking and eventually premature collapse.
Worse you could end up spending a lot of money and achieve little if the causes of the noise transmission aren't well understood and properly addressed.
FWIW
ONQ.
[broken link removed]
All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent persons should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
My best advice is that you should retain a competent building professional to advise you on these matters.