These drip down on to the ground and the splashback can soak the wall well above the damp-proof course.
Here the damp from the ground simply bypasses any built-in damp-proof course and soaks across the wall.
Between the two should be a damp-proof course which collects any water that runs down the cavity, channelling it out in front of the window.
When the window is set to the front of the opening, the damp-proof course in the archway finishes behind the window again, so that any water running down the cavity soaks on to the top of the opening.
A normal damp-proof course
is fitted just above ground level and its sole purpose is to stop dampness rising out of the ground and into the building.
The idea is that any water soaking through the outer wall drains down into the foundations or is stopped by a damp-proof course
, then channelled back out through the wall to the outside.
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.
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.