A roof intersection is, in construction, the point or line where two structural elements intersect or meet. In roof structures, a roof intersection is the location where two ridges or roof lines meet. The term is also used for timber joints where two beams cross over one another.
Types of intersections in construction
| Type | Description |
|---|---|
| Ridge intersection | Point where two ridge lines of a cross roof meet |
| Beam intersection | Two beams that pass over or through one another |
| Cross-halving joint | Timber joint where two beams are notched into each other |
| Services intersection | Point where pipes or cables cross one another |
Intersection in roof structures
In a cross roof or compound roof, intersections occur at the locations where:
- Two ridge lines meet
- Valley rafters and hip rafters converge
- A subsidiary roof cuts into the main roof
These points require extra attention for:
- Watertightness: proper lead flashings or sealing tape
- Structural strength: sufficient fixings
- Drainage: water must be able to flow away freely
Cross joints in timber
- Half-lap cross joint: both timbers are notched halfway and slotted together
- Full cross joint: one timber passes through fully, the other is notched around it
- Bearing cross joint: one timber sits on top of the other, fixed with a bolt or nail
Tips for the DIYer
- At a ridge intersection: use a ridge piece or splice plate for extra strength
- Always carry out waterproofing at roof intersections with leadwork or EPDM
- For timber cross joints: avoid weakening the timber by more than half through notching
Related terms
- Cross roof: roof formed by two intersecting gable roofs
- Valley rafter: internal angle timber of a roof
- Hip rafter: external angle timber of a roof
- Ridge beam: horizontal timber at the highest point of the roof