Why flashing matters so much
The slate itself sheds water well. The weak points are the joints. Older flashing was often made of thin metal that rusts or cracks with age, and earlier repairs may have been done with tar that dries out. When flashing fails, water runs into the wall or down the chimney, sometimes far from where the stain shows up inside.
On a slate roof, good flashing is usually copper or another long-lasting metal, worked in with the slate rather than tarred on top of it, so it lasts as long as the roof around it.
Signs of a flashing problem
- Water stains on the ceiling or wall near the chimney
- Rust, holes or loose metal in the valleys
- Tar or caulk smeared along the chimney or walls
- Damp or crumbling brick in the attic around the chimney
- Loose or missing slates along the ridge
See how to spot slate roof damage and restoration and leak repair.