Weep/Air Vents in Cavity Wall

[greyam100]

Hi folks.

Upstairs bedroom window (see photo), the internal timber cill gets damp during periods of wind driven rain.

Thereafter, water appears along top edge of the ground floor window directly beneath this one - water leaks down through the internal mastic seal along the top edge of the uPVC frame.

House is mid 80s timber frame with cavity wall & rendered blockwork (Scotland).

Having tarted up the external sealant to no success, I am suspecting rainwater may be getting blown in the air vent/slot above the bedroom window (see photo). Hence I am thinking of shielding it off somehow, to see if it prevents the ingress, but have some reservations.

Is the main purpose of that air vent to let any moisture inside the wall (which presumably falls downward) evaporate and rise back out at the top air vent?

I don't know for sure but I suspect it is a precast concrete lintel over the window opening, as you can see the concrete lintel over the back door of the garage, albeit the garage is only single leaf rendered blockwork

There are several same vents along the very bottom of this gable end and one other above the adjacent window out of shot.

The slot vent measures about 58mm x 6mm wide - thinking of a plastic/rubber bung/stopper to push in rather than faffing about with mastic gun on a ladder - not good with heights. And if makes no difference I'd take the seal back out again.

 

[Alastairreid]

The sealant around the window looks blown.

 

[greyam100]

So, the sealant around both upstairs & downstairs windows was thoroughly replaced last year by my good self; the reveals & cills were all cleaned up, cracks carefully chase out and filled, then sealed with masonry paint prior to externally sealing around the windows. It was an utter ball-ache of a job (given I had to remove upstairs glass to access it properly).

The underside of the upper cills has been sealed where the roughcast butts against the underside.

Upstairs window cill no longer gets wet.

Problem is, when rain is blowing against this gable end, I still have quite a bit of water ingress coming down through the top of the window beneath.
I haven't blocked up the weep vents yet.

I'm trying to to figure out what a cross-section through the top of the window looks like.
There an no weep vents above the 3m long downstairs window to drain water out. (same for all other houses in street).
So I am presuming it is a concrete lintel spanning 3m over the window.
Inner leaf is timber frame.
Anyone know what the cavity tray/cavity drainage detail is for this type of construction?
Just don't understand why the water is coming inwards rather than going straight to ground or being channeled outwards as would be with a steel lintel - presume I'd see the outside edge if it had been constructed with steel lintels.

House is in Scotland, built circa 1985