Why does lead flashing fail on a slate roof?
Lead flashing weatherproofs the junctions a slate covering alone cannot, around chimneys, dormer cheeks, valleys, and abutments against walls. It typically fails through a combination of age related fatigue from thermal movement (lead expands and contracts with temperature more than the surrounding materials), corrosion, and physical damage, rather than simply wearing out on its own timescale the way slate does.
A great deal of what looks like a slate problem, a damp patch near a chimney breast, water tracking down inside a dormer cheek, actually originates at a flashing junction rather than in the slate field itself. Correctly diagnosing which one you are dealing with matters, because the repair is quite different.
Common flashing failure points
- Chimney stacks. The flashing where a chimney passes through the slate covering (soakers, stepped flashing, and a chimney back gutter behind the stack) is one of the most common sources of water ingress on older roofs.
- Dormer cheeks and heads. Dormers introduce several vertical and sloping junctions in a short space, each needing its own flashing detail.
- Valleys. Where two roof slopes meet at an internal angle, lead lined valleys carry a concentrated volume of water and are prone to wear at the point of greatest flow.
- Abutments. Where a roof slope meets a rising wall, such as a taller neighbouring building.
What a small repair can and cannot fix
A small, localised flashing repair, such as re-dressing a piece of lead that has come loose or patching a short section, is within the scope of the small slate and detail repairs we take on. A full renewal of the lead flashing across a chimney stack, or extensive re-leading of valleys and abutments across a whole roof, is a larger job, and one we do not carry out ourselves. Where that is what a roof needs, our full roof replacement guide explains how we handle pointing you toward someone suitable.
Email us photos of the roof and what floor it’s on, or how many levels up it is, and we’ll tell you what we need to give you a price.
Think a flashing junction might be the real problem?
Email us photos of the roof and what floor it’s on, or how many levels up it is, and we’ll tell you what we need to give you a price.
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