retro fitted trickle vents - nightmare

[ExpertGlazing]

It's a funny one because the window has been fitted almost flush to the outside of the brick leaving it exposed to the elements. It would have been a tricky seal and doesn't look as though it has been done professionally. I would definitely take a look at the seals around the window, maybe clean them off altogether and start again. I doubt that the window has been foamed and so do this before the window is resealed. Check beneath the sill as well. Looking at the picture it could be a gap in the seal beneath the sill, the warmth from your house can draw in moisture and it looks worse at the bottom of the reveal. As suggested clean out the weep vents as well if possible.
One other possible cause of condensation could be that the drainage in the frame could be blocked. Externally glazed windows are notorious for holding a lot of water, you would have to remove the glass to check this though and with its location that will be tricky.
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[lostheadnail]

thanks for the steer on this problem folks. I will follow this very useful advice .. if I remember I'll let you know how things worked out when we reach the other side of the coming winter.

 

[noseall]

Your problem is simple to diagnose.
The windows have been incorrectly fitted and you have a cold/damp breech.

They have not been fitted far enough back (towards the room inside) in the outside leaf and have left some of the external masonry visible from the inside. BAD.
You should be able to see at least 30mm of the external masonry once the window is fitted. Chop the reveal plaster off and you will see the back side of the outer masonry and the vertical DPC. Not good.

Window wants taking out, plaster hacking back and re-fixing further back into the room. The best position is when the window actually covers the vertical DPC. Fitters don't like doing this because it makes drilling more difficult.