When water finds its way past a chimney or wall flashing, the first question is almost always the same: can it be patched, or does the whole thing need to come off? Both answers occur in practice, and the wrong one is costly either way. Replace a flashing that needed only re-pointing and you have paid for metal and labour you did not need. Patch one that is worn right through and you will be back on the roof within a year. The decision depends on what has failed, how widely, and how sound the lead and the wall behind it still are. Below are the tests we apply.
Find the actual fault first
The flashing is the lead trim that closes the joint between roof and wall, held in a groove cut into the masonry above and laid down over the tiles below. It can fail in several places at once without looking dramatic. Before deciding between repair and replacement, we want to know which of these has happened.
- The pointing has failed. The mortar that holds the top edge into the wall has crumbled, leaving the lead loose and a gap for water.
- The lead has lifted or slipped. Wind or movement has pulled an edge out of its chase or off the tiles below.
- The sheet has cracked. A split has formed at a corner, a fold or a step, usually from thermal fatigue.
- Something else has been added. Sealant, bitumen strip or cement has been smeared over a gap, often more than once.
- The surroundings have moved. A cracked chimney, a pot that is shifting or a wall that is bulging has opened the junction from outside.
Each of these has a different remedy, and most are fixable if the lead is still healthy. Our guide to the signs a lead flashing is failing helps you recognise what you are looking at from the ground or the loft.
When repair is the right answer
A repair makes sense when the metal is sound and the fault is limited. These are the cases where we would recommend it.
Failed pointing with sound lead. Raking out the old mortar, re-wedging the lead and re-pointing the joint is a small job, and it restores a flashing whose only problem is the bed. It is one of the commonest repairs we make.
A lifted edge. If the lead is otherwise flat and unbroken, it can be dressed back into place and held with lead clips or wedges. The cause matters: if wind lifted it, the fixings were probably too few, and we add them.
A small, isolated split. A single crack at one corner, with surrounding lead in good order, can be repaired by lead welding or soldering in a patch, or by replacing that piece. The aim is to remove the weak spot rather than cover it.
One length of a longer run. On a long wall abutment made of several pieces, a failed section can be replaced alone, with new lead overlapped with the old.
When replacement is the right answer
Replacement becomes the sensible choice once the lead has simply worn out, or when the original was specified wrongly in the first place. The signs usually come together.
- Cracks at several corners or steps, not just one, showing the metal has work-hardened throughout.
- Sheet that is thin, pitted or rippled, with pinholes where it has corroded.
- Edges that no longer sit tight to the wall and cannot be dressed back because the lead is stiff and creased.
- Pieces that are far too long for their position, so they have crept down the slope and torn at the fixings.
- A history of repairs, each one adding another patch, with the leak returning in a new spot.
- Lead of the wrong code, too thin for the job, which no amount of re-pointing will fix.
If the flashing is covered in layers of mastic and bitumen strip, the underlying lead is usually hidden and the surface preparation for any new work is harder. We strip back to the lead or the wall to see what is there. Our page on lead codes explains what the replacement should be made from, and our guide to how long lead flashing lasts covers the working life you can expect.
Why sealant is not a repair
It is tempting, and some roofers do it, to run a bead of mastic or an adhesive strip over a leaking flashing and call it fixed. Sealant fails to do the real job for three reasons. It bonds to dirty, damp or crumbling surfaces poorly. It cannot take the movement lead goes through every day, so it cracks within a season or two. And it hides the fault: the leak seems to stop while the lead underneath keeps moving, the pointing keeps loosening and the water finds another way in. A sealant job can sometimes buy a few weeks to get through a bad spell, and as a stop-gap it has a place. As a repair it does not. We cover the subject in more detail in our answer on whether lead flashing can be repaired with sealant.
| What we find | Usual decision | Reason |
|---|---|---|
| Crumbled pointing, lead flat and sound | Repair | Re-wedge and re-point, no new metal needed |
| One lifted edge, otherwise good | Repair | Dress back and clip, add fixings |
| Single crack at one corner | Repair | Replace that piece or weld a patch |
| Cracks at several corners | Replace | Fatigue is general, not local |
| Lead too thin or too long for position | Replace | The specification was wrong from the start |
| Layers of sealant over old lead | Strip and then decide | The real condition is hidden |
What the wall and chimney are doing
A new flashing is only as good as what it is fixed to. If the brickwork has frost damage, the joints are soft or the chimney stack leans, the chase will not hold lead for long. In those cases the right answer includes masonry work. A chimney with crumbling pointing may need repointing before the lead goes back, and one with a cracked flaunching (the mortar cap round the pots) needs that dealt with too. The chimney itself is covered under our chimney repairs service, and where lead sits round a chimney we handle that part together with the stack work so there is one set of scaffolding and one visit.
Cost and how it shapes the choice
Published UK guides quote about £250 for a patch repair to a chimney flashing, and put the average for renewing chimney leadwork near £570, with £350 at the bottom and £920 at the top. A four-sided chimney flashing is quoted at around £525 without scaffold or about £1,000 with. The fixed quote itself only comes after a survey, and the full set of figures and what pushes them up is on our page about lead flashing replacement cost.
The simple test is the price of a repair against the price of replacement, weighed by how long each is likely to last. A repair costing under half a replacement and giving years of further service is good value. A repair costing a large share of replacement and leaving old, fatigued lead in place is not. Scaffold is a big factor: if scaffold is needed for the repair anyway, the extra to renew the flashing properly can be modest compared with coming back later.
Timing: when a repair cannot wait and when replacement can
If water is coming in now, the first job is to stop it, and that is a repair in the plainest sense, whatever the long-term plan. A temporary seal or a quick re-wedging can get a house through a wet week while a proper replacement is booked. What we avoid is letting the stop-gap become the plan. Flashing leaks tend to damage the roof timbers slowly: a wet wall plate or a damp rafter end rots over a winter or two, and a stain on the ceiling is the late warning. So a small repair that buys time is fine, as long as the follow-up is on the calendar.
Replacement, in turn, rarely needs to be rushed. If the lead is old but not leaking, we would suggest tying the work to other jobs that need access, such as re-pointing the stack, renewing tiles around it or replacing the roofline. That keeps the scaffold cost to one visit. Replacing in the spring or summer is easier, because mortar sets better in mild, dry weather and lead is easier to dress when it is warm.
What a good repair looks like afterwards
A finished repair should be hard to see. The lead sits flat against the wall with a clean pointed joint at the top, no sealant bead, and laps that run the right way so water is carried down and out. At a step flashing, each step should be turned into its mortar joint, not stuck to the face of the brick. If you can see silver cracks in the bedding, sealant at the edge or new metal that has been left bright and untreated, ask the roofer to explain. We photograph the finished detail and send it to you, so you have a record of what was done and where.
Questions to ask before agreeing
- What exactly has failed, and can you show me a photograph of it?
- If you are repairing, what is the cause, and how does the repair remove it?
- If you are replacing, what code and what piece lengths?
- Will the top edge be wedged and pointed, or sealed with mastic?
- Is the brickwork sound enough to hold the new lead?
- What does the guarantee cover, and is it in writing?
An honest roofer can answer all of these on the spot. If you are told that a flashing is "done" without being shown, ask for a photograph.
How we decide on your roof
The surveyor climbs to the junction, handles the lead, checks the pointing and the wall behind it and photographs the lot. You see what we saw. If a repair will hold, we say so and price that, even though a new flashing would pay us more. If replacement is the better value, we set out why and quote for the full job at a fixed price in writing. A written 10-year workmanship guarantee goes with the finished job. More on our lead work generally is on the lead roofing and leadwork page. To book a look, phone 01256 213956 or WhatsApp a picture of the stack.
