A gutter that leaks does damage slowly. A drip at a joint wets the same patch of wall for months, so the stone or render below goes green and then damp. Overflow over the front lip soaks the fascia board, and the rot that follows spreads to the soffit (the board under the eaves) and the rafter ends behind. Inside, a damp patch near an outside wall can be traced back to a gutter that has been spilling beside it.
Most leaks come down to four causes: a joint seal that has perished, a run that has lost its fall (the slope towards the outlet), brackets that have let the gutter sag, or a blockage that sends water over the edge. This guide is about all four. If your trouble is one spot where the gutter turns, our answer on the gutter overflow at the corner deals with that single point. For the rest of the service, see guttering, soffits and fascias.
Where the water is coming from
Before anything is mended, work out which kind of leak it is. The pattern on the wall is the quickest clue, and you can read it on the next wet day from the garden or the pavement, without a ladder.
Reading the signs
A drip or stain directly below a joint points to a failed seal. A stripe of wet running down from the front lip, or a waterfall over the edge, points to overflow, either because the gutter is full or because it is holding water that cannot reach the outlet. Water pouring from the back of the gutter, behind it and down the fascia, suggests the gutter has pulled away from the board or tilted forward. A damp patch under a downpipe junction is a pipe problem, covered in our downpipes guide.
Watching it work
Pour a bucket of water into the gutter at the high end, or use a hose, and watch. Where it drips, there is your joint. Where it stands in a pool, there is the dip. Where it spills over at a corner, look at the corner. Doing this on a dry day is more reliable than guessing during a storm, because the flow is controlled and you can repeat it.
Then climb or have someone climb to look. Many causes overlap: a perished seal on a gutter that also sags is not fixed by new sealant alone.
Perished seals and joints
Plastic and aluminium systems are built from short lengths joined at unions. A union is a small clip-on piece lined with a rubber seal or a bead of sealant that makes the joint watertight. Over time the seal hardens, shrinks and splits, and the joint begins to weep. Older systems that rely on sealant alone are the same: the sealant dries and the joint opens.
Why joints go
Seals perish through age and through movement. A plastic gutter expands and contracts as the temperature changes, and a union that is fixed too tightly cannot move with it. Debris trapped in the joint grinds against the seal. A joint that sits just above a bracket that has sagged is under strain it was never designed for.
The repair
Where the union is sound, the joint is taken apart, cleaned back to bare material, and refitted with a new seal. Where the union itself is cracked or distorted, it is replaced. Sealant smeared round the outside of a failing joint rarely lasts, because the water is escaping from the inside, and it also hides the fault. On cast iron, the bolted joint is re-made with fresh sealant and a clean bolt; our cast iron gutters guide covers that case.
If one joint has failed because the seal is old, others of the same age are likely to follow. We check all of them while the access is in place.
A gutter that has lost its fall
A gutter should slope gently towards its outlet so water runs to the downpipe and does not stand. Makers of domestic systems usually specify a gentle slope, somewhere from about 1:600 to 1:350 depending on the product. In plain terms, that is a drop of a millimetre or two for each 600 or 350 mm of run: too little to see by eye, which is why a run that has lost it is easy to miss.
What goes wrong
When the fall is wrong or has been lost, water lies in the channel. Standing water carries silt to the low points and settles there, and the debris then holds still more water. In frosty weather the water can freeze and force joints apart. A gutter that is dead level or falls the wrong way will leave a sheet of water along its length, and every other fault in it is made worse.
Why the fall changes
Brackets loosen, fascia boards warp, and a heavy load of leaves or snow bends the gutter. Sometimes the fall was never right: a run on a long elevation may have been set out by eye and run a little shallow at one end. On an old building, the fascia itself may not be straight, and the gutter has followed it.
Putting it right
The fix is to take down the affected stretch, check the fixings and the board, and refix it on a line that drains to the outlet. Where the fascia has dropped, the brackets are packed or the board repaired first. Our guide to gutter fall explains how the line is set out and checked.
Sagging runs and failed brackets
A gutter hangs from brackets, and the brackets hang from the fascia or the rafter feet. If any link weakens, the run droops between supports and holds water in the dip. Manufacturer guidance for small domestic systems gives bracket spacings of 500 mm for one range and no more than 900 mm for another, and closer in areas of heavy snow. Check the maker's instructions for the system you actually have, because the figure depends on the product.
Common reasons for a sag
Too few brackets, or brackets spaced too wide, will let a run bow under the weight of water and leaves. Brackets can be bent, snapped or pulled out of soft timber. A fascia board that has rotted behind its paint cannot hold a screw. And a gutter that has been used as a ladder rest has often been pulled out of true.
Repair and replacement
A single bent or missing bracket is a quick job. Where the screws no longer bite, the options are to fix to the rafter feet if they are sound, or to cut out the rotten section of board and replace it first. Sagging that runs along a whole elevation points to a run that was under-supported to begin with, and extra brackets may be needed. Our guide to the bargeboards and verge timbers covers the neighbouring boards on the gable ends, where a similar failure shows up.
When we find a sag, we photograph it and check the timber behind before quoting, so the quote covers the board and brackets, not just the gutter.
Blockages that turn into leaks
Blocked gutters are the simplest cause and the most common to treat first. Leaves, moss and silt narrow the channel, and when rain arrives faster than the outlet can pass it, the channel brims and the surplus drops over the front lip or behind the gutter. A blocked outlet or a plugged downpipe does the same job.
Clear first, then judge
Before blaming a joint or a bracket, clear the run and test it again. Some apparent leaks vanish once the channel can move water. Our gutter cleaning guide sets out how often to clear and how to do it safely, and the answer on a blocked downpipe covers the vertical pipe.
When it still overflows
If a clean gutter still overflows in heavy rain, the cause is usually one of three things: the outlet is too small or too far from the run's far end for the roof area it drains, the fall is shallow, or the roof is delivering more water than the gutter profile can take. A shallow half-round or a small plastic profile on a long, steep slope will overflow in a downpour even when immaculate. A second outlet, a deeper profile or a larger system is the cure.
Roof causes
Water can also arrive at the gutter in the wrong place. A slipped tile or a broken drip edge sends the flow behind the gutter and not into it, and a poor eaves detail lets rain skip the gutter completely. If water runs down behind the gutter in every shower, the roof edge needs a look as well.
Repair, replace or re-hang
The right fix depends on how many faults a run has and how old it is. A fault that stands alone, such as one perished seal or one bent bracket, is a repair, and we say what else we looked at and found sound. Three or four faults on one elevation usually mean the run is worn out as a whole and mending it piece by piece will not hold.
What the options cost
MyBuilder's 2026 price guide puts guttering at £30 to £70 per metre and scaffold at £20 to £40 per m² as national typical ranges for roofline work. They are guides, not quotes. Our price follows a survey and covers access, removal, new gutter, brackets, fixings, timber repair and clearing away.
Lifespan and the long view
One trade blog, Pureseal Services, writing in December 2025, gives uPVC a life of 10 to 20 years, aluminium 20 to 30 and cast iron 40 to 70, sometimes more. It is a single source and low confidence, but it shows why a ten-year-old plastic run with several failures is a candidate for replacement, whereas the same number of faults on sound iron is more likely to be fixed. Our gutter lifespan guide goes into the evidence.
What you get from us
A survey from a safe working height, photographs of the leak and its cause, a written quote and a plan for the access. Repairs and new work are covered by a 10-year workmanship guarantee, in writing. The old materials are taken away.
To get a view before we visit, send a photograph of the stain on the wall, one of the joint or corner above it, and a note of when it leaks: in light rain, only in heavy rain, or all the time.