Why is my gutter leaking at the corner or seam?

Last Updated: October 23, 2026

Leaks start at the joints

A gutter leaking at a corner or seam is leaking at a joint: one of the places where two pieces of metal meet and the only things keeping water in are fasteners and a bead of sealant. Gutters of Kent repairs and installs gutters across Kent and South King County, with the work done by licensed and insured contractors, and joint leaks are one of the most repairable gutter problems when they are caught while the joint itself is still sound. The question is whether the sealant has failed on a good joint, or whether the joint itself has failed. That difference decides between a quick gutter repair and replacing parts of the run.

Where the joints are

Even a seamless gutter has joints. The long runs are formed in one piece, but every system still has:

• Inside and outside corners, also called miters, where two runs meet at an angle. Water moving along the gutter slows and swirls at a corner, and debris collects there, so corners carry more standing water than straight runs.
• End caps, the closures where a run stops. They are crimped or riveted on and sealed, and they sit at the high end of the run, where any standing water from poor pitch ends up resting against them.
• Outlets, the drops where water leaves through the bottom of the gutter into the downspout. They are fastened and sealed into a hole cut in the trough, and they carry the most water of any joint.
• Section seams on sectional gutters, where pre-made lengths are lapped together every 10 feet or so. Seamless runs avoid these, which is why they have far fewer places to leak. The seamless vs sectional comparison explains the difference.

Why joints fail

Sealant ages

Gutter sealant is a flexible bead that bonds two metal surfaces and fills the gap between them. Over years of sun, water and temperature swings it hardens, shrinks and loses its grip on the metal. The first sign is often a slow drip from the underside of a corner during rain, or a dark, wet streak below an end cap.

The metal moves

Aluminum and steel expand in warm weather and contract in cold. A long run fixed tightly at both ends pushes and pulls on its corners and end caps through every cycle. If the sealant cannot flex as much as the joint moves, it tears away. This is one reason long runs are hung so they can move slightly in their hangers.

Poor assembly

A joint that was never tight, with gaps the sealant was asked to bridge, or rivets that missed, or a miter cut out of square, will leak sooner than a well-made one. Sealant applied over dirt, oil or oxidized metal never bonds properly in the first place. Where a joint has been resealed several times and keeps failing, assembly or movement is usually the underlying problem.

Corrosion

Steel gutters rust once their coating wears through, and cut edges at joints are where the coating is thinnest. Aluminum resists corrosion, but it can corrode where it touches copper, or steel fasteners, or where wet debris sits against it for long periods. A corroded joint cannot hold sealant, because there is nothing solid for it to bond to. The best gutter material guide compares how each metal holds up.

Sealant failure versus joint failure

This is the distinction that decides the repair. Look closely at the leaking joint, ideally when it is dry:

A good reseal is more work than it sounds. The old sealant has to come out completely, the metal has to be cleaned of dirt and oxidation and dried, and the new sealant has to be a product made for gutters and the metal involved. Squeezing a new bead over an old one, on a wet day, rarely lasts. Where a corner is bent, the rivets have pulled or the metal is thin, a new corner piece is the better repair.

When standing water is the real cause

A joint that leaks between storms, dripping for hours after the rain has stopped, is sitting in water. That means the run is holding water it should be draining: the pitch is too flat or reversed, the gutter has sagged, or the outlet is partly blocked. Sealant under constant water fails much faster than sealant that dries out between storms. Fixing the joint without correcting the fall leaves the next leak waiting. The gutter slope guide explains how fall is set, and why gutters sag covers runs that have lost their line.

Some drips that look like joint leaks are something else. Water running down the back of the gutter from the roof edge is covered in the guide to water behind gutters, and water spilling over the lip at a corner is overflow, covered in why gutters overflow.

Why Kent’s season makes small leaks bigger

A corner that drips a little during one storm may not seem urgent, but in Kent it gets a lot of storms. NOAA’s 1991 to 2020 normals for the Kent station average 96.7 days a year with at least a tenth of an inch of rain, with about 6.23 inches in November alone. A leaking corner drips onto the same patch of fascia, soffit and ground on each of those days, and over a winter that can soften the board behind it and wash out the soil below. The dry months, July and August averaging under an inch each, are the practical time to reseal, because sealant needs clean, dry metal to bond.

Sectional gutters with many leaking seams

On a sectional system, seams every few lengths mean many joints, each aging at the same rate. When one starts leaking, the others have had the same years of exposure. Resealing them one at a time can become a recurring job, and each reseal is only as good as the metal around it. At that point the comparison is between ongoing joint repairs and replacing the runs with seamless gutters, which reduce the joints to corners, end caps and outlets. Gutter replacement explains what that involves, and the repair vs replacement guide works through the decision.

What to do next

Note exactly where the drip comes from and whether it happens only in rain or afterward. If it is one tight joint with old sealant, a careful reseal is a reasonable repair. If the joint is loose, bent or corroded, or the run holds water, the scope is larger. Either way, the repair should end with water run through the joint to confirm it holds and the downspout carries it away. You can Get an Estimate for the repair, or use the problem checker to sort what you are seeing first.