How Much Lead Flashing Do I Need?

How We Calculated This

Lead flashing is measured in linear metres. You need to identify each location where flashing is required:

• Chimney (typical): Front apron (~1m) + 2 side step flashings (~1.5m each) + back gutter (~1m) = ~5m total
• Wall abutment: Measure the full length where the roof meets the wall
• Valley: Measure the valley rafter length + 300mm overlap each end
• Pipe flashing: Use a pre-formed lead slate instead

Lead Code Guide (BS EN 12588)

• Code 3 (1.32mm): Soakers, small flashings under 450mm girth
• Code 4 (1.80mm): Most common — flashings, aprons, abutments
• Code 5 (2.24mm): Valleys, gutters, larger flashings
• Code 6 (2.65mm): Parapet gutters, box gutters
• Code 7 (3.15mm): Heavy-duty applications
• Code 8 (3.55mm): Very heavy-duty, rarely used domestically

Standard Roll Widths

• 150mm: Soakers
• 240mm: Step flashings
• 300mm: Cover flashings, aprons
• 450mm: Valley linings, back gutters
• 600mm: Wide valleys, parapet gutters

Typical Domestic Quantities

• Single chimney re-flash: ~3m of Code 4, 300mm wide + ~2m of Code 3 soakers
• Lean-to abutment (3m): ~3.5m of Code 4, 240–300mm wide
• Valley (3m long): ~3.5m of Code 5, 450mm wide

Tips

Always use milled lead sheet to BS EN 12588 (look for the BSI Kitemark). Cut lead with tin snips and dress it with a lead dresser or bossing stick. Chase into mortar joints at least 25mm deep and seal with lead sealant. Allow 150mm overlap at joints. Lead is recyclable and has a 100+ year lifespan when properly installed.