Water leaking in through top of pvc window frame

[john77]

During storm Darragh we got water dripping in through the top of the window frame in the kitchen, enough to wet three bath towels we put down to catch it. The window is north facing and the wind and rain were blowing directly onto it, but the other north facing windows in the house were OK. The water came in through the middle of the window frame, not the ends. But on inspection afterwards the silicone seal along the top of the frame on the outside seems to be intact, except for a hole in each corner.
Could these have been the entry point for the water, and, if so, what is the best way of blocking them up? They're about 1cm square.

 

[SpecialK]

What is above the window? The roof could be leaking down the cavity or a window above?

 

[john77]

I suppose it's possible for it to have been coming down the cavity. There is a window above but it didn't show any signs of leakage. The windows are all 10 years old but we got the sealant renewed last September.
I will try and get a look in the loft and in the gutter for signs of problems.

 

[john77]

Forgot to attach the photo!

 

[SpecialK]

Forgot to attach the photo!

What often happens is a hole/crack in a roof tile makes water run down the felt. The felt rots away near the gutter and this water then ends up on the soffit board. It then runs across the soffit board which probably sits on the external wall and runs down the cavity. This then runs down the cavity and hits the window. This is why modern construction calls for cavity trays which would divert the water outside.

Solution is to find the leak and fix it. Install eaves support boards so any water running down the felt ends up in the gutter.