Valley Gutters in Lead: Design, Sizing & Installation Guide
Valley gutters are critical drainage details where roof slopes meet. Correct sizing, bay lengths, and falls are essential to long service life. This guide shows how to design and install valley gutters in lead to Leadwork Standards, with practical tips and product links.
1. Choosing the Right Lead Code
Valleys carry high volumes of rainwater. Code 5 rolled lead sheet is standard, but Code 6 may be used for wide or exposed valleys. Thicker codes resist fatigue and sagging. Review our rolled lead sheet codes guide for weights and thicknesses.
2. Falls & Drainage
Valleys should be laid to a minimum fall of 1:80 (12.5 mm per metre). A steeper fall is preferred for long runs or heavily shaded roofs. Adequate fall prevents ponding and prolongs service life.
3. Bay Lengths & Jointing
Lead valleys must be divided into bays to allow thermal movement. Keep bays to 1.5 m max length for Code 5 and 2.0 m for Code 6. Overlap bays by 150 mm with welted joints or steps as per Leadwork Standards.
4. Underlays & Support
Use a continuous underlay such as geotextile over the substrate. Ensure boards are smooth and adequately ventilated. Sharp edges or rough boarding must be avoided to prevent wear-through.
5. Fixings & Expansion
Fix only at the head of each bay, never along the length. Allow free movement down the slope. Clips at edges should be stainless or copper, cut long enough for thicker codes. Avoid nailing through the sheet.
FAQs
What lead code is best for valley gutters?
Code 5 is generally used, with Code 6 preferred for wider or high-exposure valleys.
How long should lead valley bays be?
1.5 m maximum for Code 5, 2.0 m for Code 6. Overlaps must be at least 150 mm with correct jointing.
Do valley gutters need underlay?
Yes. Always use a suitable underlay such as geotextile. It reduces condensation and prevents abrasion.
What fall should a valley gutter have?
At least 1:80 (12.5 mm per metre). A steeper fall is better for long runs or roofs with heavy water flow.
Can I nail lead valleys directly?
No. Fix only at the head, using clips at edges. Nailing through the length causes fatigue and splits.
Next in the series (Post 4): Lead Dormer Roofs & Cheeks — specifying codes, bay sizing, and movement joints for long-lasting details.
