Rainwater leaking from balcony into kitchen below, nobody can tell me why

[3473]

Property is approx 10 years old, I moved in last year

I recently noticed the area below my balcony railing is a lot more wet than the neighbours:

Today this water has started to leak into the kitchen directly below it:

The platform of the balcony (where people stand) has recently been felted so thats not the issue. It's the bit directly below the railing.

The railing sits on multiple stones, between which there is concrete. I noticed some small gaps in the concrete, which I have now put silicone on top of, but it hasnt really solved anything

Any idea what the problem is? Thanks

 

[3473]

In addition I have noticed that the neighbours have this extra "black layer" under their stones..is this what I need? They are on holiday so I can't ask at the moment:

 

[Nige F]

Neighbours have had a cavity capping retro fitted = should have been done when built. Ask them and contact your house insurers - you might get some £ for damage.

 

[^woody^]

No DPC below the copings and no cavity tray.