Mystery leak, any ideas?

[Overadecade]

We had a bad storm last night and we has water leaking onto one of our downstairs windows. I totally expected there to be a bit of missing caulk from the pvc window directly above but can't see anything obvious. There was, however water sitting inside the frame of the upstairs window. Could this be the cause of the leak downstairs? Will add some photos in a minute.

@PigletJohn wondered if you might have any thoughts.

Bumping for you but I can’t see the photos OP?

Could the water have been blasted in through any minuscule gaps in the window frame (if it’s an opening window)? in the upstairs window. Do you have cavity walls it could have run down inside?

Just guessing as I’m not piglet John but hopefully he or someone more knowledgeable will be along soon.

The walls are granite with lath and plaster interior walls so there is a gap that the water will likely be running down. I just can't work out where it is getting in!

It’d be worth having a look when it’s raining at the down pipe coming across from the flat roof, the build up of what looks like moss/ stuff from the roof could indicate a bit of a blockage / maybe the water is flowing too fast there.

That's just bitumen. Whoever did the flat roof last didn't do a tidy job! It is quite a bit away from there it is coming in too, middle of the window pretty much.

We had water coming in above the frame of our French doors. Turned out it was coming from the upstairs window which was directly above. The bit where the outside concrete sill meets wall was horrible sealed and it was running down the inside frame. £5 for new sealant from Amazon.

I think you have a stone sill above and would guess it is coming in through a crack or gap. The strong wind might have blown it it. It is probably tilted slightly so that water would usually run to the outside. The plastic window will have drain holes in the frame intended to help water flow outside. Check the sealant above the window and go the side. A selfie stick may help.

One day you will pull off the L&P to add insulation and reline, you may be able to see more when the inside of the windowframe is exposed.