Cracking lead
Why does lead crack on a roof?
The short answer
Lead cracks mainly because it moves. It swells a little when warm and shrinks when cold, and a piece that is too long, or fixed so it cannot slide, tears itself over the years. Thin lead, foot traffic and old patches add to it. A small crack can sometimes be repaired, but a pattern of cracks usually means renewing the section.
The main reasons lead splits on a roof, what you can spot from the ground, and how a lasting repair differs from a patch.
Lead moves with the temperature
Lead is a soft metal and it expands and contracts as the day warms and cools. The movement in a single day is small. Over a flashing that is metres long, and over thousands of days, it adds up. If the sheet is free to slide a little, nothing happens. If it is pinned hard at both ends, the metal has nowhere to go and eventually splits, usually at a fold, a corner or a nail hole.
Good leadwork allows for that movement. The sheet is cut in lengths that suit the detail, and joins are made as laps, rolls or drips so each piece can shift. When a roofer ignores this, cracks are the typical result, and they may take a few winters to show. A split across the width of a flashing, with clean edges and no sign of impact, is the classic pattern, and it often appears first where the lead is fixed hardest.
Pieces cut too long or fixed too tight
Length is the usual culprit. A single run of lead along a long wall or across a wide roof area looks neat for the first season, then fails as the temperature swings. Fixing is the second. Nails driven through the face of the lead, or clips that grip it so hard it cannot move, stop the sheet working. Our page on lead rolls and drips shows how a properly built roof lets lead slide, step by step.
On a flat or gently sloping roof the details matter even more, because standing water and foot traffic add stress. The cause is not the age of the metal. Lead can last decades when detailed correctly: MyJobQuote's September 2026 guide credits lead flashing with well over 80 years, so early cracks point at the fitting and not at the material. A roofer who cuts long runs to save on joints saves a few minutes on the day and creates a repair for later.
Thin lead, poor support and foot traffic
Lead sheet comes in codes, from code 3 at 1.32 mm up to code 8 at 3.55 mm in Royston Lead's cast-lead brochure. A light code used where a heavier one belongs gives you thin metal that tires sooner. The right code depends on the detail and the roofer's specification. Our guide to lead codes sets them out side by side.
The surface under the lead matters too. A rough or uneven deck, a loose board or a sharp edge can work on the lead each time it moves. Foot traffic does the rest. Lead dents and tears under heels, especially in a box gutter or on a flat roof used for access to chimneys, aerials or solar panels. Wherever people have to walk, a board or walkway protects the sheet, and it is worth asking about when a quote is prepared, since it costs little beside a renewed gutter lining.
Repair, weld or renew
One clean crack in a sheet that is sound everywhere else can be repaired, and the repair can hold for years. Small splits can be closed by lead welding, or a new piece can be let in, which our page on lead welding and bossing explains. Sealant or self-adhesive tape over a crack keeps water out for a while. Both hide the fault and do nothing about the movement that caused it, so the crack tends to reopen.
If you can see cracks at several points, patches from earlier repairs, or thin lead worn through, the better route is to renew the section with lead cut and fixed to allow for movement. The survey tells you plainly which applies, with photographs of each fault. If a repair will hold, we price the repair and explain why, rather than recommending more work than the roof needs. Doing the least that will hold is how we prefer to work.
What it costs and what to do next
Checkatrade's roof repair guide, updated October 2026, lists lead flashing repairs at £50 to £70 per metre, plus VAT. Access, the number of splits and the type of roof change the total, so the figure is a starting point and nothing more. For a patch at a chimney, MyJobQuote gives £150 to £250. You get the quote in writing once we have surveyed, with a single total on it, before agreeing to anything.
If you have noticed a stain, photograph it and note the date, then tell us where it is. Working with lead in cold conditions has its own cautions, which matter most in a freeze. For everything else we do in this metal, start at the lead roofing and leadwork hub. Keep a note of when cracks first appear, since a pattern across several winters helps the roofer see whether movement is the cause.
Related questions
Cracked lead questions
Is a hairline crack in lead worth worrying about?
It is worth having looked at. A hairline crack can let in water in driving rain and often grows as the lead keeps moving. A roofer can check whether it is isolated and say if a small repair will hold.
Can cracked lead be painted over to stop leaks?
Coatings and paints may slow a drip for a short time, but they do not stop the lead moving, so the crack tends to reopen. Welding a repair or renewing the section deals with the cause.