A gutter joint is the weakest point in a run of guttering, because it is the only place where two separate lengths depend on a seal rather than a single piece of material. Leave a joint dripping through a wet winter and the water has somewhere to go: down the face of the fascia, into the soffit boards, or behind the gutter onto the top of the wall. The stains on the brickwork and the green tide mark below the joint are often the first sign.
The cause is not always the seal itself. A bracket that has loosened, a run that has lost its fall or a joint that was never pushed home can all look like a failed seal from the ground. This guide takes the causes in the sequence a roofer works through them and explains when a reseal is a sensible repair. If the whole run is the problem, our gutter replacement cost guide covers what drives the price.
Where the water is really escaping
Before blaming a joint, work out where the water leaves the system. A gutter can lose water in four main places, and each points to a different repair.
The first is the joint itself, where a union bracket or a bolted connection joins two lengths. The second is the back edge of the gutter, where water spills over the rear lip and runs behind the run onto the fascia or the wall. The third is a corner or stop end, where a moulded fitting meets the straight run. The fourth is the outlet, where the gutter drops into the downpipe. A leak at the outlet often turns out to be a blocked pipe below it, which is why our guide to downpipes is worth a read if the water pours out near the pipe.
Is it dripping or overflowing?
A steady drip from the underside of a joint after a shower is a seal problem. Water pouring over the front lip in a downpour is not a leak at all: the gutter is blocked or too small for the roof area it serves, and sealing the joints will not change that.
Which side does the stain appear on?
Staining on the face of the fascia below a joint means the seal has gone. Staining on the wall behind the fascia, or damp patches on the soffit, suggests water is spilling backwards over the rear lip, often because the run has sagged.
Why a plastic gutter joint stops sealing
Most modern plastic guttering is joined with a union bracket: a clip with a rubber seal that grips both lengths. The seal depends on a clean, flexible rubber lip and a gutter pushed fully home up to its expansion mark. Plastic moves with temperature, growing longer in summer heat and shrinking in cold snaps. A run cut too tight, or pushed in past the line, has no room to expand. The joint is squeezed in summer and pulled apart in winter, and the seal loses its grip a little more every year.
Rubber also ages. It hardens under sunlight and frost, picks up grit and leaf mould, and cracks where it was folded during fitting. Sometimes a previous owner has smeared silicone along the outside, which rarely reaches the actual fault on the inside face where the gutter holds water.
What about the clip itself?
Plastic clips crack after years of sunlight, particularly where a bracket bolts to the fascia. A joint that gapes open while the seal looks intact usually has a broken clip.
Can a seal be replaced?
On many systems, yes. The rubber gasket can be swapped, the joint cleaned and the gutter reseated, provided the plastic is still sound. If the clip is split or the gutter ends are cracked, replacing that section is the sounder repair.
Cast iron and older metal joints
Older houses in Swindon and the surrounding villages often still carry cast iron or early aluminium guttering. Lengths of cast iron overlap at a socket and are bolted through a lip, with a bed of putty or mastic between the faces. Over time the mastic dries and shrinks, the bolts rust and seize, and the faces pull slightly apart. The result is a slow weep at the joint, usually with a rust-coloured stain down the fascia or wall.
Refitting a joint means undoing the bolts, cleaning both faces back to bare metal, applying fresh jointing compound and bolting up again with new galvanised or stainless fixings. Where the bolts have rusted solid, the repair is slower and may need the section lifting out.
The condition of the iron matters more than the joint. A gutter rusted through along its base, or cracked by frost where water has sat in it, is beyond jointing. Surface rust can be cleaned and painted, but pitting that has eaten into the metal will keep leaking whatever is done at the joint. Our guide to cast iron gutters explains how to judge which side of that line a run is on.
If the guttering is on a listed building or sits in a conservation area, ask the council what it expects before swapping cast iron for plastic.
Brackets, spacing and fall
A joint that leaks may be reacting to the run around it. Brackets screwed to the fascia or the rafter ends decide how far a full gutter can sag. FloPlast's installation guide for its MiniFlo system gives a maximum of 500 mm between fascia brackets on straight runs, while Brett Martin advises supports no more than 900 mm apart and closer in areas of heavy snow. The figure depends on the system, so the installation sheet for the product is the reference.
Where brackets are spaced too widely, the gutter sags between them. A sagging length holds standing water, loads the joints on either side and pulls them apart. A bracket that has worked loose, or sits in a softened fascia, lets the whole run drop and the neighbouring joint opens.
How much fall should a gutter have?
Gutters need a gentle fall towards the outlet so water keeps moving. Brett Martin suggests 1 mm for every 600 mm, and FloPlast recommends 1:350 where the system is fitted to a fall. A gutter that is level, or falls the wrong way, holds water against the joints. Our guide to gutter fall explains how to check it.
When does a leak mean the fascia is failing?
If screws pull out with no resistance, or the board behind the bracket is soft, the problem sits underneath the gutter. Our guide to uPVC fascia lifespan explains how long boards typically last.
Finding the leak before you call anyone
You can learn a good deal from the ground. Choose a dry day, run a hose gently into the gutter at the high end, away from the outlet, and watch each joint in turn with a helper who can see the run from the other side. A joint that drips or sprays shows itself within a minute or two. Keep the flow gentle so you do not push water over a lip that would not spill in normal rain.
If you cannot do that safely, wait for steady rain and look from the garden. A joint running wet while the straight lengths either side are dry has almost certainly failed. Photograph it with the zoom on your phone, because those pictures are useful when you ask for a quote.
What signs should I look for in the garden?
Look for a vertical green or black streak on the wall below a joint, flaking paint on the fascia, dark rings on the soffit and plants growing from the gutter itself. A joint that has leaked for a long time may leave the brickwork permanently damp, and in winter that dampness can freeze and crack pointing.
Should I climb up and look?
Only from a footed ladder with someone holding it. Work at the first-floor edge of a house is better left to someone with scaffold or a tower, because the repair needs both hands and good access. Our survey photographs show the joints and fascia, so you can see the fault without going up yourself.
Reseal, refit or replace the section
The right repair depends on what the survey finds. If the gutter is straight, well supported and the plastic is sound, a worn gasket can be replaced and the lengths reseated, which is a modest job. If a few brackets have loosened, refixing them to solid timber and adding supports where spacing was wide often cures the leak without touching the joint.
A bead of silicone can slow a drip for a few weeks, but it needs a dry, clean surface to bond, which a working gutter rarely offers, and it traps dirt that makes the proper repair harder later. Treat it as a stopgap.
Replacement of a section or the whole run makes sense when plastic has gone brittle, when several joints leak at once or when the fascia behind needs replacing anyway. MyBuilder's cost guide, updated on 21 August 2026, quotes £30 to £70 per metre for replacing guttering, with scaffold often adding to the total on a two-storey house. Those are typical national ranges. Access, length of run, material and the state of the fascia decide the price, with a written quote sent after the visit.
Replacing a gutter is the moment to check the fascia and soffit behind it. New guttering on boards that are about to fail wastes the work.
The work comes with a written 10-year workmanship guarantee, and the old guttering leaves with us once the site is tidy. Blockages are often why a joint failed early, so the gutter cleaning guide is a useful companion.
What a leaking joint does to the rest of the roofline
A joint that weeps all winter does more damage than the drip suggests. Water running down the fascia keeps the finish wet, and on timber boards it soaks into the end grain at the bottom edge. Boards that stay wet soften, and a soft fascia can no longer hold a bracket firmly. The gutter drops further, the joint opens more, and the cycle accelerates.
Behind the gutter, water can reach the ends of the rafters, the timber under them and the soffit. A soffit that stays damp grows mould and algae on its underside and may sag or drop away. Our guide to mouldy soffits describes what that looks like, and the guide to bargeboards covers the gable-end equivalent.
Can a leaking gutter cause damp indoors?
It can. Water running down the outer wall can saturate the brickwork and push damp through to the internal plaster, appearing as a stain near the ceiling. It looks like a roof leak, but the covering may be sound, and a survey separates the two.
Do I need the whole roofline done?
Not if a single section is the culprit and everything else is holding up. Our advice is the smallest repair that properly cures the leak, and the quote spells that out if a reseal or a few new brackets will do. The main gutters, soffits and fascias page lists what else we can check on the same visit.