Damp appearing around this sliding door top corner. New extension built just 3 years ago - cavity wall with render top half and slate cladding bottom half.
Previously been fine and signed off by building control etc.
There is a bath in the room above this area but it’s not been used for many months.
We have no idea as to the cause of this issue. Could it be the roof but can’t see any obvious cracked tiles.
Advice would be v much appreciated as causing a lot of stress.
Thanks in advance