A welted edge is a short, flat folded-back edge on a lead flashing or on zinc sheet, a few centimetres wide, that acts as a water check. The metal is turned back on itself so a double thickness with a closed fold is formed. The Dutch name for this detail is klisrand.
That simple fold does three things at once. It breaks the capillary path, so water cannot creep back along the underside. It stiffens the edge, so thin lead or zinc will not flutter or curl. And it makes the edge safe to handle: a folded edge does not cut.
Where it applies
- The lower edge of lead flashings — at abutments to chimneys, dormers and rising brickwork, so that running water drips off at the fold instead of tracking inwards
- Zinc gutter and cladding work — as stiffening and water check at the free edge
- Drip and throating details — where water has to be forced to let go
- Flashings over openings — where a creeping droplet would land directly behind the frame
On some prefabricated lead products the welt is already formed in the factory.
Practical tips
- Turn the edge over 20 to 30 mm — enough to be stiff and effective, little enough to stay neatly flat
- Use the right tool — a folding bar or seaming pliers gives a crisp, closed fold; a hammer on a block of timber leaves waves in the lead
- Work lead gently — lead is soft and stretches easily; fold in one movement and do not work the same spot repeatedly
- Allow for movement in zinc — zinc moves considerably with temperature; run long lengths with expansion joints and do not fix over the full length
- Lap and fall — a welt is no substitute for adequate lap. Keep an upstand of at least 80 to 100 mm on flashings and make sure the surface below has fall
- Hygiene with lead — wash your hands after handling lead and never work it with abrasive tools; lead dust is harmful
Related terms
- Lead sheet
- Zinc sheet
- Gutter
- Rainwater drainage
- Roof tile
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