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Roofing · code · weight
How much lead flashing do I need?
Lead by code and girth, cut into pieces no longer than 1.5 m — the limit the old sheet worked to, and the one the Lead Sheet Association still gives for expansion.
1
Measure it
Every box has its own unit next to it.
Change the unit beside any box and the number converts. The (i) beside each question says what the box wants and where the figure usually comes from. Anything marked per cent is a percentage of the quantity above it.
2
Check the rates
Rates and assumptions used
These are the figures the calculator works to. Change any of them and the order list updates — your merchant’s pack sizes and your own waste allowances beat the defaults every time.
How this one works
Pieces = run ÷ maximum piece length, rounded up
Total length = run + a lap on every piece
Area = total length × girth, weight = area × the code weight
Strips per roll = roll width ÷ girth, rounded down
The figures the calculator works to. Every one can be changed in step 2, and your merchant’s pack sizes and your own waste allowances beat these defaults every time.
Rate
Default
Why
Roll width
600 mm
Common widths are 150, 240, 300, 450 and 600 mm.
Roll length
3 m
Standard lead roll. 6 m rolls are also sold.
Clips at
450 mm
Holds the free edge down in the wind.
Lap per piece
100 mm
Minimum 100 mm on a flashing, 150 mm on a shallow pitch.
Patination oil
12 m²/L
Stops the white staining running down the brickwork.
A worked example
With the defaults the page opens on:
How long is the flashing? 8 metres
Which code of lead? Code 4 — general flashing
What girth? 300 millimetres
Longest piece you will use? 1.5 metres
Lead
Pieces: 6 no. — max 1.5 m each — expansion
Length with laps: 8.6 m — +100 mm lap a piece
Area: 2.58 m²— × 300 mm girth
Weight: 52.7 kg— code 4 at 20.41 kg/m²
Strips per roll: 2 — from a 600 mm roll
Rolls: 2 × 3 m
Fixing
Lead clips: 18 no. — at 450 mm centres
Lead wedges: 18 no. — into the chase at 450 mm
Patination oil: 1 × 1 L — about 12 m² a litre
Sealant: 2 tubes — pointing over the wedges
Change any figure above and every line recalculates; the small print under each row is the sum that produced it.
Questions people ask
Which code of lead do I need?
Code 4 for most flashings, code 5 for anything carrying water such as valleys and aprons, code 3 for soakers, 6 and up for exposed or parapet work. The code sets the weight per square metre the calculator uses.
Why cut lead into 1.5 m pieces?
Expansion. Longer pieces tear as they move. 1.5 m is the limit the old sheet worked to and the one the Lead Sheet Association still gives for flashings; valleys can go to 2 m.
How is the weight worked out?
Total length (run plus a 100 mm lap per piece) × girth = area, × the code weight in kg/m². Code 4 is 20.41 kg/m².
Read before you order. These work out quantities, not structural design — spans, lintels, rebar and foundation depths need an engineer and Building Control sign-off. Waste allowances are defaults, not promises: awkward cuts, long runs and bad weather all eat more than 5%. Where a merchant sells whole packs, the figure is rounded up to whole packs.
