I work in the construction industry, and I'm starting to come across cases of problems with cavity filled insulation. Dry-lining with insulation on the inside of the walls is a much more preferable solution.
Apparently this combination is a good method for heat insulation and damp prevention.
However it's a problem for non-detached houses. Even if you haven't a lazily built party wall, and one which hasn't been compromised by having blocks cut or left out for floor joists, you've might now have as much or more sound leaking in from the non-party walls.
Effectively sound will resonate around the empty cavity when doors are slammed, as doors and windows are sitting in the cavity. Even relatively normal levels of noise can travel from a room via the window through the cavity and in next doors windows. I was explaining this to a builder of semi's (100's of them) and while he agreed it seemed like he'd never considered this before and felt adding cavity insulation afterwards would be a great solution.
Irish (UK really) building regs are particularly poor when it comes to sound. And in reality most people would put up with a cold house than one where the neighbours wake them up on a regular basis, so sound should come first.
Interesting points Sorehead. However, insulating to prevent heat loss, and sound proofing, are two different procedures / requirements.
For preventing heat loss - you only need to insulate the exposed external walls. There is no need/advantage in insulating party walls.
For sound proofing (b) - you only need to insulate the party wall (with a sound-proof insulation). Propagation of noise within the cavity is unavoidable, unless you fill in the cavity locally at the vertical line of the party wall. This would not be advisable, as it could cause a cold-bridge. The ideal solution is to form a cavity within the party wall, which rarely happens in Ireland (or in any other country).
I agree that the Irish (& UK) building reg.s are very weak on sound proofing.