My brother has just brought a c1920's terraced house. The houses along
the terrace are paired and it's the dividing wall between the paired
side that's causing the problem (i.e. front door next to front door).

From the non-paired side the noise is about what I would consider to
be "normal" i.e. muffled sounds. If someone was shouting you would
hear it but otherwise nothing more than thuds and maybe the faint
sound of voices if everything was quiet.

The paired side is another story. On this side you can hear
*everything* clearly. The wall appears to be double thickness house
brick. (not sure if there is a cavity or not).

On lifting a few of the floor boards it appears that the joists
supporting the floor are actually joined between the houses on the
problem side. There are 10mm gaps around the joists where they are
passed through the brickwork.

Does anyone have any ideas on how to reduce the level of noise ?

I had the following idea of:

1) Filling the gaps around the joists under the floor with expanding
foam.
2) Hardboarding over the floor to seal up any gaps between the boards
3) Gap filling under the skirting around the edges of the floor
4) Fitting a good quality carpet underlay
5) Fitting a good quality carpet.

Any ideas on whether this is likely to help the situation? I have read
other posts on this forum which talk about building a stud wall but am
not sure if this will help if the adjoined joists are the cause of the
problem.

Thanks,

Andy.