Parapet & Box Gutters in Lead: Detailing & Installation Guide
Parapet and box gutters are heavy-duty rainwater channels designed to cope with large volumes of water. Correctly detailed parapet gutters in lead ensure durability and prevent costly failures. This guide covers codes, bay sizes, falls, and fixings in line with Leadwork Standards.
1. Selecting the Lead Code
Parapet and box gutters require heavier lead codes. Code 6 is a minimum recommendation, with Code 7 or 8 used on wider spans or exposed sites. These resist distortion and fatigue under water load.
2. Falls & Outlet Positioning
Provide a fall of at least 1:80. Outlet positions should be well-sized and placed to minimise ponding. Multiple outlets may be necessary on long runs. Falls should always direct water towards outlets without flat spots.
3. Bay Sizing
Divide gutters into bays. Maximum bay length is 1.5 m for Code 6 and 2.0 m for Code 7. Bays should overlap by 150 mm with welts or steps. Expansion joints are essential on long runs.
4. Substrates & Underlays
Substrates must be smooth and free-draining. Use suitable geotextile underlay to prevent abrasion. Timber boards should be well-ventilated to reduce condensation risk.
5. Fixings & Edge Details
Fix only at the head of bays. Edge weltings, drips and splash guards must be detailed correctly to stop overflow into the building fabric. Stainless or copper clips are required for restraint without restricting movement.
FAQs
What lead code is best for parapet gutters?
Code 6 is the minimum. Code 7 or 8 is often used on wide or exposed gutters.
How should parapet gutters be laid?
In bays no longer than 1.5–2.0 m, with laps of 150 mm. Use expansion joints where necessary.
Do parapet gutters need underlay?
Yes. A geotextile or felt underlay prevents abrasion and condensation, extending service life.
What fall should be provided?
A minimum of 1:80. Greater falls are recommended on long runs or where outlets are limited.
Can parapet gutters be one continuous sheet?
No. They must be divided into bays with expansion joints to accommodate thermal movement.
Next in the series (Post 6): Flat Roofs in Lead — design considerations, bay sizing, underlays and expansion joints for long-life coverings.
