Symptom - dark staining on the bricks on the first three layers from the parapet - apparent on front side (prevailing wind side only). The parapet is above a single storey extension, extended in 1995. No evidence was evident in 2003. Parapet is a cavity brick with a top layer of bricks laid across the cavity. There is lead flashing on the inside cavity joining the flat roof.
In 2003 the same ground floor extension was further enlarged and the parapet was extended for a further nine feet. In 2008 I first noticed the black discolouration on the first three layers of bricks exactly to the left of the new parapet extension - ie in the earlier extension's parapet wall - about 9 feet in width also.
I am considering - repointing and remortaring the top bricks - most look fairly sound - though there is a small flaked off piece near where the new parapet connects with the older one on the top of the wall.
Should I also add coping stones on the parapet wall? Would these solve all problems?
Could there be a problem with the lead flashings that join the flat roof to the rear of the parapet - ie joining the newer extension flashing to the older one? Is this likely and is there a remedy?
Thanks for reading this. All advice appreciated. :?: