Leadwork
Lead flashing pieces, lead length and weight
- where
- number of pieces
- length of the run to weather (m)
- end lap between pieces (mm)
- maximum length of one piece (m)
- total lead length (m)
- length of each piece (m)
- weight of lead (kg)
- girth of the flashing (mm)
- lead thickness (mm)
- density of rolled lead (g/cm³)
Explain this equation
Splits a run of lead flashing into pieces no longer than the recommended maximum, then works out the total length and weight of lead to cut from the roll.
Pieces are limited in length so thermal movement does not tear them, and each joint overlaps by the lap l_p. The first piece covers its whole length; each further piece only adds its length less the lap. Rearranging gives the number of pieces n, rounded up (and at least one). The total lead includes the laps, so is the run plus one lap per joint. Weight is length × girth × thickness × density, with the 1000 sorting out mm against m and g/cm³.
Same laps arithmetic as underlay courses, followed by volume times density.
Sense check: a 4 m run with 1.5 m maximum pieces and 100 mm laps needs 3 pieces, 4.2 m of lead in total, each 1.4 m. At 150 mm girth in Code 4 that is about 12.9 kg.
Watch out: the maximum piece length depends on the code and use. Take it from LSA guidance, not just the roll length.
Splits a flashing run into pieces no longer than the recommended maximum, allows for the laps, and gives the length and weight of lead.
Enter your values to see the result.
Good to know
Lead Sheet Association guidance limits flashings to pieces no longer than 1.5 m, lapped at least 100 mm end to end, turned into the joint at least 25 mm and wedged. Clips go at about 300–500 mm centres depending on exposure. Girth is the full width of the strip before dressing (for example turn-in plus upstand plus cover).
Common mistake
Fixing one long length to save time. Long pieces cannot take up thermal movement and will crack or creep.
Limits
Straight run. Corners, step flashings and soakers need their own allowance. The weight uses nominal thickness.
Sources
- Building Conservation (Lead Sheet Association): The ins and outs of weathering to walls (flashings ≤1.5 m, 100 mm end laps)
- BLM British Lead: sizing guide (Lead Sheet Association maximum sizes: flashings 1.5 m; flat roof drips and joints by code)
- Robert Price fitting guide: rolled lead flashings (no piece over 1.5 m; clips at 300–500 mm)
- BLM British Lead: weight chart (BS EN 12588 codes 3–8, thickness and kg/m²)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the roof covering manufacturer’s fixing specification, BS 5534, BS 8000-6, BS 6229, the Lead Sheet Training Academy guidance and Building Regulations. Wind uplift and structural design need a competent designer.