Soundproofing tips - extreme situation

Soundproofing a floor will not be as cost-effective as soundproofing the ceiling below it. Is that even an option for you? Most acoustics will not bridge an air/surface interface, but if the building is as rigid as you say, lower frequencies are going to transmit the best throughout anyway. Floor joists are far easier to work with (from below), but if that is truly a concrete slab, it will want to resonate (if properly driven from below).
 
If the cost of soundproofing will exceed your deposit, it is very much worth considering following your gut instinct. Don't throw good money after bad.

only mass soundproofs.
 
here, i'll say it again........
 
only mass soundproofs.

When I built my studio, I was careful to ensure the internal "room" wasn't touching the outer room (i.e. wood touching wood), so it's resting on expanding foam. I figured regular polystyrene would probably compress under the weight and the effect would be lessened. The internal walls are just regular pasterboard (wallboard) on a wood frame. I then filled the space between the inner and outer rooms with rock-wool.
 
If you do go down this route make sure you screw the floating floor frame to the main floorboards at regular intervals  before applying the foam, otherwise it will literally raise the whole room up as it expands.... I made this mistake first time!
 
You can then remove the screws once the foam has set, use a craft knife to remove any overlapping foam, and put down the internal floor boards.
 
I put fibreboard underlay on top of the floorboards, then covered it in a gel-backed (i.e. bathroom) carpet.
 
I use Behringer Truth B2030A monitors which are 150W/75W RMS, and at full volume you can't hear anything from the outside.
 
It's very quiet inside, however the only thing that comes through *from* the outside is very loud and low bass frequencies, such as big trucks or big destroyers trying out their fog-horns (really). I spoke to a colleague about this who did sound-proofing as part of his physics degree, and he said nothing short of a very thick concrete wall would keep those kind of sounds out.
 
So I guess you could construct a floating floor this way... if you don't mind losing 3-4 inches of height in your room.
 
M.

burgerproduction
I've seen many projects for raised/floating floors for studios, but this seems to be to prevent drums or noise from within the room leaking out.
 

What prevents sound getting out will also prevent it getting in. The problem is that low frequencies in particular are really hard to keep out. Especially if a problem in the flat below is something like a hi-fi with speakers on the floor that in turn connects to the walls and the sound then travels through them and up to your flat that way as well as directly through the floor. Steel joists can also be excellent sound transmitters through a building.
 
The noise can almost certainly be kept out, but expect to lose quite a bit of height in the flat because the floor will end up raised several inches (at least). The walls might also need several inches of soundproofing added to them.
 
Which in turn means floor loading may become an issue, because effective low-frequency blocking requires non-resonating/vibrating mass to be effective. And depending on the materials used there may also be fire prevention implications as well.
 
Reducing transmitted noise by a few dB often isn't too difficult. But reducing it to an acceptable level might be much harder, and the more reduction is needed the harder it gets. The law of diminishing returns sets in pretty quickly, hence the "room inside a room" approach to studio building.
 
One option might be to lay wooden joists on top of the floor. Fill the gaps between them with the heaviest grade of rock wool, then suspend another floor on top which is isolated from the joists by weight-supporting rubber blocks such as Auralex U-Boats.
https://www.auralex.com/p...u-boat-floor-floaters/
 
Assuming the floor can support the weight of course.
 
Things like electric sockets might need moving depending on how close to the floor they are in the first place, and the total cost (and weight) will obviously depend on the size of the flat. Then there are the walls to consider - if sound is travelling up them from below they'll need treating as well. And the doors would obviously need adapting if the floor height is raised.
 
All in all, quite possibly a big and expensive job.
 
And maybe the flat's selling at the price it is because of the problems with the neighbour below it....

The house attached to ours has been owned for about 15 years by a landlord who specialises in providing accommodation to young people coming out of care for the first time or with mental health issues needing a "half-way house" between hospital and moving on. Which means the landlord has to be good, legally compliant and above board and all the rest or he doesn't get tenants referred to him any more. Basically he's the opposite of the "bad landlord/Rachman" figure.
 
We have never had a problem with any of those tenants at all. What can happen is sometimes other people latch on to someone and basically abuse the situation in all kinds of ways. If professionals aren't involved resolution can be slow and very difficult if not impossible. I have worked with a lot of mentally ill people, never had a problem and would be happy to have most of my ex-clients as a neighbour, but moving next to what you describe isn't something I'd knowingly do.
 
There was once an almost continual middle of the night party and music noise issue with a young guy who worked for the landlord staying there for a few weeks. He had a lot of mates who treated the house like a party venue. I was tempted to retaliate via the nuclear option and dig out the Orange, Fuzz Face and Telecaster, crank everything to 11, prop guitar against speaker and go away for the weekend but Mrs TLW though that would have been a Really Bad Idea.
 
So had to settle for a quiet world with the landlord instead. Which did the trick. But when the problem is an owner-occupier things are much stickier.