Why Important
Leadwork is formed by a series of laps and steps and is not sealed. If water builds up it can find its way over up-stands and leak into the building.
What to look for
Acid run-off is caused by algae that forms on slates, generally on the shaded pitches, and manifests as pale grey staining on the lead, eventually wearing a hole in the lead. Leadwork in gutters can fail because: The sizes of the sheets are too big, or badly fixed, causing the lead to crack. Joints between pieces of lead have been badly formed and are unsound. The material has worn thin and reached the end of its life, or has been damaged by acid run-off from slate roofs.
When to look
Lead gutters should be cleared out regularly and inspected for problems at the same time.
Outlets from parapet gutters need to be regularly cleared of leaves and debris or they will become choked, causing the downpipe to backup and overflow back onto the leadwork.
How to fix
Old sand cast lead is thicker than lead available today and new sheets of lead may need to be laid in smaller pieces requiring the timber base that the lead is formed over to be redesigned or adjusted.
Lead gutters can be protected by inserting sacrificial pieces of lead flashing tucked under the bottom row of slates and secured with lead clips.
When these sacrificial pieces wear thin they can easily be replaced.
Small holes in lead can be repaired with a lead- welded patch.
These ‘Hot Works’ involve using a Geotextile underlay blowtorch in the proximity of timber and must therefore be carefully watched as there is a small chance that the heat could cause a smouldering fire in timber sarking below.
If, however, the cause of the lead’s failure means that the gutter is likely to fail again, it will eventually be necessary to renew the lead sheet.
This should always be carried out by a suitably qualified lead plumber to a design by an architect or surveyor qualified in conservation.
Avoiding creating problems
Parapet and valley gutters often suffer physical damage from foot traffic or nails and debris being stood on and piercing the lead. Damage can also happen if loose slates slip down the roof and cut through the lead. Problems can occur if the gutter boarding under the lead starts to rot or the boards have been laid without proper falls, causing the water to pond and find its way into the building.