Even if it doesn't land on a wall tie, it can drop to the bottom and bridge across the damp-proof courses at the bottom of the wall, creating a similar bridge but in this instance appearing like rising damp.
These drip down on to the ground and the splashback can soak the wall well above the damp-proof course.
Of course, there should be a cavity tray damp-proof course
above the flashing to stop any water draining down the wall and past the flashing but deep snow on the roof can cover the evidence, hence the unfinished surveys.
Many or even most older homes now have courses inserted retrospectively into the main supporting walls but almost without exception no damp-proof course
was installed retrospectively into the walls that support the floors, and that's where they are needed most.
A half-brick-thick garage wall will not keep out driving rain but a cavity wall will, providing we take care over the position of the damp-proof courses
The previous floor to the coal house and scullery had not been replaced and when laid in the 1920s, damp-proof courses were restricted to the posh parts of the house, certainly not the scullery and coal house.
The answer was to incorporate a damp-proof course in the floor but this would involve digging up and relaying the concrete.
These trays are basically damp-proof courses
, but at high level.
This is done by damp-proof courses
called cavity trays manufactured for this purpose.
While the window is out, it is essential to double-check that the damp-proof courses
are in position and sound.