What actually causes even slow walking sounds from the upper floor to be heard? I'm not sure where else to ask this question but I thought this might be sort of a relevant place. It's a question that's bothering me for a long long time.
I'm staying in an apartment where there's a large penthouse above our flat occupied by one of the builder-partners of the apartment. In fact, the penthouse in question covers the area of four flats underneath. I do believe that the penthouse was not originally planned to be constructed there; it was an afterthought.
The problem is that while the penthouse occupants are annoyingly noisy, even the walking sounds can be heard in our flat. It's not even fast and aggressive walking, but a slow-paced normal walking. Not just that, when they drag around the water pipes to water the flowers, the noise that comes through is extremely annoying. It is almost as if someone has encroached on your property. What I find incredible is that even if some tiny object is dropped on the upper floor, it can be heard at the bottom floor loud and clear. The point I'm trying to make is, even simple activities in the upper floor becomes noisy and annoying, which makes me wonder if the concrete roof above us is super thin?
That question has been bothering me for a long time. What is actually causing that noise? Is it just the thin roof or are some other factors coming into play?
Also, next to my bedroom is the kitchen of the neighboring flat - a common wall between my bedroom and the neighbor's kitchen. The noise that comes through is almost as if there's no wall at all.
 A: two things cause this, as follows.
First, note that the ceiling of your flat is the floor of the penthouse. If that floor/ceiling is too flexible (i.e., insufficiently rigid) then even slow walking sounds will be readily broadcast by it right into your flat.
Second, if the floor of the penthouse is insufficiently dense (for example, plywood sheeting over wooden floor joists instead of a concrete subfloor slab with ceramic tile on top) then upstairs sounds will not be reflected back into the penthouse space but will be transmitted down into your flat.
If the penthouse was added as an afterthought, then it is possible both conditions are present, and you have an unsolvable problem on your hands.
A: I had this issue when I was an architecture student living in college. Oddly, the sounds came not from the bedsit above but the next one along, diagonally up to one side.
Assuming that it really is the flat above that is your problem, there are several reasons why the sound is coming through:

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*Inadequate structural mass. A heavy floor vibrates less than a lightweight floor, which means quieter sound. Additional covering upstairs or adding material between the joists - I have known sand be used - will help. Fixing a massive false ceiling from below can be effective but is expensive.

*Inadequate sound absorption. Porous materials such as carpets upstairs, lagging between the joists or acoustic tiles downstairs can help. Gaps must be kept to an absolute minimum, as sound tends to find its way round the edges.

That last was in fact my problem; the building structure left small but acoustically transparent gaps at the junctions of the horizontal and vertical surfaces.
Much the same issues apply to the party wall between your flats. However what worries me here is fire resistance; in the UK at least, that kitchen wall should have good fire resistance and that almost always means good sound insulation. I'd suggest you check that out.
