Chapter 1: Why does the ceiling stain appear below the side wall where our Rooksdown house meets the porch roof?
What we find
Where a roof slope runs into a wall, such as a porch, a bay or a two-storey section stepping down to a single-storey one, the joint between roof and wall is sealed with a flashing. On many estate houses of this age that seal is a mortar fillet, a sloping bead of cement pressed into the angle, and not a lead flashing. Mortar does not stretch. As the house settles and the weather cycles it, the fillet cracks and lets go of the wall.
Water follows the crack and soaks into the wall or the timber behind it before it shows indoors, so the stain often appears days after the rain that caused it. It is usually patchy, brown at the edges and growing slightly with each wet spell. Looking from a ladder, you might see the fillet standing proud of the wall, or a clear line of daylight between the cement and the brick. This is a repair that should not wait.
What we fix
We rake out the failed mortar and fit a proper lead flashing, with the top edge turned into a groove cut in the brickwork and the lower edge lapped over the tiles or sealed with soakers, so that the joint can move without cracking. Lead is the right material because it dresses tightly and lasts for decades when fitted correctly. A smear of sealant would only hide the gap for a season, and we do not use it as a repair here.
Where the flashing has been leaking for some time, we also check the batten and the underlay behind it and replace any that are wet or soft. Our guide to lead flashing against a mortar fillet explains the difference in more detail, and the work is priced after the survey, not before it.