Flashing leaks
Why do flashings leak in storms?
The short answer
Because a flashing sits on a junction, and junctions are where roofs give up first. The flashing is the metalwork, usually lead, that seals a roof against a chimney or wall. Storms push rain sideways behind its upper edge, and any lifted edge, crumbling pointing, split seam or old sealant gives that water a way in. Most flashing leaks can be repaired locally, without replacing the roof.
What a flashing does, the ways it fails in a storm, and what a repair that lasts looks like.
What a flashing is for
Where a roof meets a vertical surface, tiles or slates cannot just stop at the wall, because the gap would let water through. A flashing bridges the joint: one edge is tucked into the wall or chimney, the other lies over the roof covering, and rain runs down the metal onto the tiles below.
Round a chimney the flashing has several parts: an apron across the front, stepped pieces climbing each side and a small gutter tucked behind the stack. Along a side wall you will find a run of stepped flashings, interleaved with soakers, the small pieces of metal that sit under each tile or slate course. Roofers form most of these in lead because it can be dressed tightly into awkward shapes. Royston's cast-lead brochure lists code 4 lead and above for flashings, and code 3 for soakers only.
When the whole joint is sound you never think about it. When any part is not, water reaches the wall or ceiling beneath.
How storms find the weak spot
Heavy, wind-driven rain is the test a flashing fails. In still weather water runs down the face of the metal and off. In a gale it is driven up and behind the top edge, and if that edge is lifting, split or unsealed, the water follows the wall into the building.
The top edge is held in a cut slot in the brickwork, or a mortar joint, and sealed with pointing. Over the years the pointing cracks and drops out and the flashing loosens. A storm can then finish the job, lifting the metal and letting it flap. Some older roofs have a cement fillet in place of metal, which cracks as the building moves and the roof covering expands and contracts.
Driving rain also tests places that stay dry in a calm shower, which is why a roof that leaks only in a gale so often turns out to have a flashing fault. Our answer on roofs that only leak in wind explains the pattern.
Common reasons a flashing stops working
Several things cause failure, and they often combine. The lead may have cracked at a fold or seam after years of movement. The pointing holding the top edge may have gone. Fixings may have rusted or pulled out. A past repair may have used bitumen strip or a bead of sealant, which cracks and peels, leaving a gap that is hidden behind it.
Valleys and the abutments with dormers also deserve a look. In a valley two slopes shed their water into a single channel, so a split or a blocked lead gutter shows up fast in heavy rain. Moss and leaves can hold water against the metal too.
You may spot the signs indoors: a brown stain on a chimney breast, a damp patch beside the stack, or paint lifting near the ceiling. Those marks follow the line of the flashing instead of sitting in the middle of a room.
What a lasting repair involves
A tube of sealant does not make a lasting repair. It might stop the drip for a short while without dealing with the cause. A proper repair strips back the failed section, inspects the brickwork and mortar behind it, and fits new lead shaped to the roof, with the top edge locked into a chased slot and repointed.
For a minor failure, one run or one corner may be all that needs replacing. For a chimney with several worn sections, renewing the full set usually beats patching, because new lead beside old will move differently. MyJobQuote's guide to chimney leadwork gives a typical patch repair of £150 to £250 and a full replacement of £350 to £460 without scaffold, or £700 to £920 with it, as at 22 September 2026.
Our emergency roof repairs page covers the wider job, and the price for any repair is one figure, put in writing once the survey is done. What moves that figure is the number of junctions involved, how far the lead has to be renewed and whether the work needs scaffold to reach it safely.
Before the roofer arrives
Keep it simple and safe. Do not climb onto the roof or lean out of a window to reach it. From the garden or the pavement, take a zoomed photograph of the chimney and any wall junctions, then note where the stain shows inside and on which side of the house.
Catch the drip in a bowl and move furniture and electrics away from it. Keep clear of any ceiling that looks swollen or sagging. Our answer on water near lights after a roof leak explains when to stop and wait.
At the survey each junction at fault is photographed, so you can look at the same evidence we do, and the verdict on whether a local repair will hold is given in plain terms. Our storm damaged roof page looks at the wider picture after a gale.
Related questions
Flashing leak questions
Can a leaking chimney flashing be fixed without new lead?
Sometimes, when the metal itself is in good order and the pointing alone has let go. The roofer rakes out the slot, lays the edge back in and repoints. If the lead is split or thin it has to be replaced, because sealant on worn metal will not last.
Does a chimney flashing leak always show at the chimney?
No. Water runs along rafters and plasterwork before it drops, so the stain can sit a metre or more away from the entry point. A damp chimney breast, a patch beside it or a stain on the ceiling below are the usual signs.