burgerproduction
I've been researching soundproofing products for the past few years....it's a complicated business
I've used one product with good results Fonostop Duo is a product sold here in Italy, it's used for sound insulation, but mainly against footfalls coming from your own house. It's thin, relatively effective at blocking noise and easy to install.

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

so, has anyone tried lead sheeting? On paper lead is the best sound blocker by far.

loaded vinyl is one of the best soundproofing materials around, lead is great, sand filled cinder block walls work REALLY well, if we are talking about walls. Floors and ceilings are a different animal all together. If you have something above or below you it's a challenge, that's where room in a room construction comes in handy.
 
But as might have been mentioned before...

wait for it...

only mass blocks sound.
It isn't the whole story, but it is the best single thing you can do.

I hear what people are saying...mass blocks sound... But in practise what does that look like for a design?
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.
there are also floating floor solutions with mats, such as hushfloor, which prevent vibrations from passing from level to level. The material I mentioned Fonostop, uses a similar material to that used for rooves along with a later of synthetic fibre to create a slight elevation.
I was wondering what a combination of materials might be like, for example: Fonostop mat with a layer of lead and then another layer of hushfloor.
Lead doesn't conduct noise due to its flexible malable nature.
I'm willing to spend a fair amount of money on this as we were originally going to spend over 10,000 on underfloor heating, but the issue with noise has taken front and center.

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.

msmcleod
 he said nothing short of a very thick concrete wall would keep those kind of sounds out.
 

this
is mass.

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....

Thanks to everyone for their advice and support.
After doing some serious digging into the issue with the neighbours (and consulting experts in the area) we have decided to pull out of the sale. We might have to lose some money (and a few tears over the lost opportunity), but I cannot put my son and wife in the path of this potential bullet.
One thing I know from living in London: Kids can go through a rebellious stage, do drugs etc.. but at some point they grow up and get jobs. 30 year old junkies don't.
All your advice has been invaluable for our future house (wherever it may be) as I will be insulating any place I go against noise.

I am sorry for the situation, but once you put wife, son, and junkie in the same post, pretty much anyone would support your decision. There is much more at stake than simply money here.

mettelus
I am sorry for the situation, but once you put wife, son, and junkie in the same post, pretty much anyone would support your decision. There is much more at stake than simply money here.

Thanks mettelus, I agree. The situation is a bit more nuanced than him being a junkie, but to the best of our knowledge, he is frequented by a bad crowd, there have been 'situations' in the past, and he is under tutelage of an aunt. The problem with these types of people is that one year they can be fine, next year they can fall into a hole again....and you have to live above them.