What lead code should I use for flashing?

Code 4 (1.80mm thick, 20.41 kg/m²) is the standard for most flashings including stepped flashings, apron flashings and chimney work. Code 3 is lighter and used for small, simple flashings. Code 5 is heavier and recommended for valley gutters and exposed locations where extra durability is needed. Always comply with the Lead Sheet Association (LSA) guidelines.

How do I measure for stepped flashing?

Measure the raking length along the abutment where the roof slope meets the wall. Each stepped piece typically covers one course of brickwork (75mm rise). The flashing strips are usually 150mm wide (75mm into the wall chase and 75mm over the tiles). Order enough length to cover the full raking measurement plus 10% wastage.

What size lead flashing do I need for a chimney?

A standard chimney flashing set includes: front apron (Code 4, ~300mm wide × chimney width), stepped side flashings (Code 4, ~150mm wide × chimney depth on each side), and a back gutter (Code 5, ~450mm wide × chimney width). Pre-made chimney flashing kits are available for standard chimney sizes. You will also need to order ridge tiles and main roof tiles — see our Ridge Tile Calculator and Roof Tile Calculator.

How is lead flashing sold in the UK?

Lead flashing is sold by the roll in standard widths and lengths. Common roll lengths are 3m and 6m. The width varies depending on the application — 150mm for stepped flashings, 300mm for apron flashings, 450mm+ for valleys. Lead is also sold by weight (per kg). Prices vary significantly with the lead market price.

Can I use alternatives to lead flashing?

Yes — alternatives include EasyFlash (a lead-free, self-adhesive flashing), Ubiflex (non-lead flexible flashing) and zinc or copper flashings. These are lighter, easier to work with and avoid health concerns associated with lead. However, lead remains the traditional standard and is preferred for conservation and heritage work. Check local Building Control requirements.

Lead Flashing Calculator — Rolls, Weight and Lead Code Guide

Lead Flashing Calculator — Rolls, Weight & Code

Calculate lead flashing quantities for stepped, apron, valley and chimney flashings. Uses UK lead codes and standard roll sizes.

Flashing Type

Lead Code

Code 4 is standard for most flashings

Flashing Length

Total length of flashing needed

Roll Length

Include wastage allowance

Adds 10% extra for dressing and trimming

Wastage Percentage

10% is standard for lead work

Price Per Roll (optional)

Enter your supplier price per roll

How We Calculate This

Our lead flashing calculator determines the amount of lead you need based on the flashing type, total length and lead code. It calculates total area, weight and number of standard rolls required.

The formula

Total area = Length × Width
Weight = Area × Weight per m² (from lead code)
Rolls = Total length ÷ Roll length

UK lead codes (BS EN 12588)

Code 3: 1.32mm thick, 14.97 kg/m² — light flashings, soakers
Code 4: 1.80mm thick, 20.41 kg/m² — standard flashings (most common)
Code 5: 2.24mm thick, 25.40 kg/m² — valleys, exposed locations

Standard widths

Stepped flashing: 150mm wide
Apron flashing: 300mm wide
Valley flashing: 450mm wide
Chimney set: Combination of widths for front, sides and back

For chimney sets, the calculator estimates total length as: front apron (1m) + two stepped sides (your entered length × 2) + back gutter (1m). Adjust for larger or smaller chimneys as needed.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Lead Flashing Calculator — Rolls, Weight & Code

How We Calculate This

The formula

UK lead codes (BS EN 12588)

Standard widths

Frequently Asked Questions

Related Calculators

Roof Tile Calculator

Ridge Tile Calculator

Felt and Batten Calculator

Soffit and Fascia Calculator

Gutter Sizing Calculator