What is a roof abutment?
A roof abutment is the junction where a roof slope meets a wall, chimney or other structure that penetrates or adjoins the roof surface. This junction is vulnerable to water ingress and requires careful weatherproofing.
Why is the roof abutment important?
Where a roof slope meets a wall or chimney, rainwater can penetrate. The abutment must therefore be made watertight using:
- Lead flashings — strips of lead that are built into or chased into the wall and dressed over the roof covering
- Zinc flashings — as an alternative to lead
- Self-adhesive flashing tape — flexible strips (often lead or aluminium) that conform to the shape
Application
A roof abutment occurs at:
- Chimneys — where the chimney penetrates the roof, sealed all around with lead
- Dormers — the sides and top where the dormer meets the main roof
- Extensions — where the roof of an extension meets the existing wall
- Parapets — where a flat roof transitions to an upstand
Key considerations
- Weathertightness — the roof abutment is one of the most leak-prone areas of a roof
- Material — lead is the most durable; zinc and synthetic alternatives are more affordable
- Chase depth — lead flashings should be let into the wall by at least 10-15 cm
- Overlap — the flashing strips must extend at least 15 cm over the roof covering
Related terms
- Roof covering
- Gutter
- Dormer
- Roof structure
- Flat roof
Learn more about building terms in our knowledge base at fredsdiyplans.com.