Leaking Gutter Joints
Leaking gutter joints are caused by aged seals, thermal movement and failed unions. A joint that drips in rain wastes the gutter's capacity and stains walls below. This guide explains the causes, the repair options and when a joint should be replaced rather than resealed.
Why joints leak
Gutter joints seal two sections together. The seal material ages, hardens and shrinks. Gutters expand in summer heat and contract in winter cold, and that movement works seals loose over years. A joint that was sound for a decade can start weeping in one season.
Debris worsens joint leaks. A blocked run holds standing water against joints for longer, which finds any weakness in a seal. Clearing the run sometimes reduces a leak, but it does not repair a failed seal.
Signs of a leaking joint
Drips from a joint during rain, staining on the wall below a joint, and green growth at a joint line all point to a leak. A joint that drips only in heavy rain has a small failure. A joint that drips in light rain has a larger one.
Joint leaks are distinguished from overflow by location. Overflow spills over the front edge. A joint leak drips from the joint itself, usually at the underside, and the wall below the joint is stained in a narrow line.
Resealing a joint
Resealing replaces the failed seal material, and the union is cleaned before the new seal is fitted. The joint is then tested under flow, because a seal that looks sound but weeps under water load is not finished.
Resealing suits a sound union with a failed seal. It is a small job, and it restores the joint fully where the union itself is intact.
When to replace the union
A union that has cracked, warped or failed repeatedly should be replaced, not resealed again. Repeated resealing of a failed union wastes money and leaves the joint unreliable. Replacement fits a new union matched to the profile, and the joint is sealed as part of the same job.
Where several joints on one run have failed, the run's material may be near the end of its life. Replacement of the run, rather than joint-by-joint repair, is then the honest recommendation.
Frequently asked questions
Why do gutter joints leak?
Seals age and harden, and gutters expand and contract with temperature, working seals loose. Standing water against a joint worsens the leak.
Can a leaking joint be resealed?
Yes, where the union itself is sound. The seal is replaced and the joint is tested under flow. A cracked or repeatedly failing union should be replaced instead.
How do I tell a joint leak from overflow?
A joint leak drips from the joint itself and stains a narrow line below it. Overflow spills over the front edge of the gutter.
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Last updated: 2026-10-27