Chapter 1: Why is there a damp patch by the dormer on our Beggarwood house when the tiles look fine?
What we find
Houses of this period often have a dormer or bay with its own small roof, and the leaks come from the joints around it rather than from the tiles. Where a tiled slope meets a vertical wall, the junction is sealed with a flashing: a strip of lead or lead substitute tucked into the brickwork and dressed down over the tiles. On many developer-built roofs the top edge was sealed with a mastic line instead of being cut into the mortar, and mastic splits and shrinks as it ages.
Once the mastic fails, water runs behind the flashing and into the roof structure. The sign inside is a brown stain on the ceiling or wall near the dormer cheek, usually after heavy or wind-driven rain, and often months after the leak began. Because the tiles look intact from the garden, it is easy to blame the wrong thing.
What we fix
We trace the water from the stain back to its entry point, working through the flashing, the abutment between wall and roof, and the dormer's own roof covering. A failed mastic seal is cut out and the flashing is re-dressed and secured into a chase (a groove cut into the brick mortar joint) then pointed, which lasts far longer than another bead of sealant. Damaged lead is replaced with new, and where the lead has been stolen or lost, a permanent substitute may be used.
You see the photographs of each stage and a fixed quote for the repair, which on a leak like this is normally a half-day of careful work rather than a new roof. Our lead roofing and lead work page explains the metal, and pitched roofing covers the rest of the slope.