Leadwork
Leadwork and flashings
Valleys, abutments, chimneys and parapets. The parts of a roof that leak, dressed in milled lead rather than sealed with mastic.
How it works
Roofs do not leak in the middle. They leak where the plane stops: at a wall, a chimney, a soil pipe, a valley. Each of those is a piece of dressed lead lapped into the courses so that every layer sheds onto the one below it, and the water never has to be persuaded to leave.
Soakers go in one per course with a stepped cover flashing over them, chased 25 mm into the bed joint and wedged, not surface-sealed. Lead is sized by code and cut to length: code 4 soakers, code 5 for a chimney back gutter, and no piece longer than 1.5 metres, because lead that cannot move splits itself along the fold.
If a stack has been sealed with mastic twice, it does not need a third tube. It needs the lead chased into the joint properly.
- Lead
- Milled to BS EN 12588, code 4 and code 5
- Cover flashing
- Chased 25 mm into the bed joint and wedged
- Piece length
- 1.5 m maximum, LSA guidance, so it can move
- Valleys
- Lead-lined or GRP, on a boarded and felted valley
- Patination
- Oil applied the same day the lead goes on
- Ventilation
- Dry ridge to BS 8612, balanced to eaves
