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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.
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.
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.
Order list
The orange figure is the one you order to. Highlighted rows are the other numbers you order to. The small print under each row is the sum that produced it, so you can check it against your own take-off. Amber rows are warnings, not quantities.
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 — 8.6 m ÷ (3 m × 2 strips a roll), rounded up
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.
Calculators for the same job
Doing this for a whole job rather than one wall? SiteLedger keeps the valuations, supplier statements, invoices and variations against the project they belong to.
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.