Damp patch on loft bedroom wall and around chimney

[RadarBailey]

When it rains a damp patch seems to appear through the brickwork and onto the slanted ceiling. The room is a converted loft. The damp appears around the chimney area and seems to spread lower. The house is an end terrace with this wall facing the patch between my house and next-door.

 

[justlead1]

Hi. It is likely that the dampness is due to the masonry/bricks above the roof absorbing rain water and passing down the structure into the living area. Traditionally lead flashing is turned into the chimney 30mm the damp passes this, hence the problem. I have made a video about this problem, titled chimney tray/dpc and can be viewed at http://www.justlead.co.uk/
However the cost of fitting such to an existing chimney can be expensive. My advise would be to access the roof, when we get a couple of dry days and coat masonry with a transparent sealer. Good Luck