how you can keep 13[.5] tonnes of an incredibly dense object in an apartment

Gold's density is 19320 kg/m^3^

13500 kg / 19320 kg/m^3^ = 0.6988 m^3^

Rounding up to 1 m^3^ since gold bars don't stack perfectly.

So basically a closet can store it all. And people like this tend not to give a shit about or even be aware of silly things like "safety" or "structural load" so I wouldn't be surprised if the building's fucked from this.

Edit: Actually I got curious so let's calculate some more.

According to this website, concrete can have a compressive strength of anywhere from 5 MPa to 60 MPa. I don't know what they make apartments out of but let's go middle of the road and say 30 MPa, which is the first category where you need a design mix (mix, let cure, and test, presumably) and not a hard and fast ratio.

Assuming the gold is stacked at 1m by 1m by 1m (so it has a 1 m^2^ base).

An online converter tells me that 13500 kg is 132389.802 N, or 0.1324 MN. Pa is N per m^2^ so it would be 0.1324 MPa, a small fraction of the concrete's rated load by my non-physicist non-engineer guess.

Obviously most of the load of the concrete is taken up by the building itself, so I don't know how much load in the apartment it can tolerate, and this also assumes the gold pile is resting directly on a vertical beam and not on a horizontal beam without anything underneath. But from the looks of it (again, not an engineer), it wouldn't be nearly enough to immediately collapse the building, just eat away at the safety margins and reduce the building's lifespan.