A valley is the internal angle formed where two sloping roof surfaces meet. Valleys collect rainwater from both slopes and channel it down to the gutters, and are usually lined with lead, formed with purpose-made tiles or finished with a preformed valley system.
Because valleys carry a concentrated flow of water, they are a common source of roof leaks, so detailing and workmanship matter. Structurally, a valley is formed by a valley rafter in a cut roof, or by valley boards and infill framing where the roof uses trussed rafters. Common valley finishes include:
- open valleys lined with lead sheet or a glass-reinforced plastic (GRP) valley trough
- closed valleys formed with purpose-made valley tiles
- dry valley systems that need no mortar
For measurement and pricing, valleys are usually measured as a linear item, stating the material and width.
Related terms: rafters, ridge, hip, flashing.
