Every roof has junctions: where it meets a chimney, a wall, a dormer or another roof. Tiles and slates cannot bridge those gaps on their own, so something has to carry water across them. That something is almost always lead.
Why lead, and not a sealant
Lead moves. It expands and contracts with temperature without cracking, it can be dressed to the exact shape of the brickwork it sits against, and it lasts for decades. Sealant does none of that. A flashing repaired with a bead of mastic will fail again, usually within a couple of winters, because the sealant is being asked to survive movement that it cannot.
What good lead work looks like
- It is chased into a mortar joint and wedged, not stuck to the face of the brick.
- It is in sensible lengths, so each piece can move independently rather than tearing.
- Around a chimney there are separate elements: front apron, side soakers and step flashings, and a back gutter.
- It is the right code, or thickness, for the job. Too thin and it splits at the folds.
When it needs replacing
Look for splits along a fold line, lead that has lifted away from the wall, white powdery corrosion, or previous repairs in mastic or flashband. Any of those on a chimney is worth acting on, because chimney flashing failures show up inside quickly, usually as a damp patch on a bedroom ceiling near the stack.
The awkward truth about cost
Proper lead work is not the cheapest quote you will get, because it is cut and dressed on site to suit the actual roof rather than fitted from a kit. It is, though, the part of a roof most worth spending on, because it is the part that decides whether the rest of it stays dry.
