Can I just seal the joint with silicone?

It is the most common homeowner attempt and it reliably fails. Gutter joints are designed to move as the plastic expands, and sealant cannot do that — it cracks, then funnels all the water out of one point instead of a spread drip. Replacing the gasket is cheaper and actually lasts.

Why do gutter joints leak in summer as well as winter?

Because plastic expands. If the gutter was pushed fully into the union with no expansion gap, warm weather forces the joint open and it leaks worst on hot days. That is a strong clue that the assembly is wrong rather than the gasket being worn.

Should I replace one joint or the whole run?

One perished gasket is a one-joint fix. Several failing at once means the whole system is the same age and the rest are next, so replacing the run often works out better value than repeated call-outs — especially if scaffold or a tower is needed each time.

Can I mix gutter brands?

Not reliably. Profiles look similar but the exact dimensions differ between manufacturers, so a union from one system will not seal properly on another's gutter. Identify the existing system and match it, or replace a whole run in one product.

Low risk

Updated 30 August 2026

Gutter Leaking At A Joint

Water drips steadily from the join between two lengths of gutter, or from a corner, even in light rain.

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What's happening?

Plastic gutter is supplied in lengths joined by union brackets, corners and stop ends, each sealed with a rubber gasket that the gutter clips into. The gasket does the waterproofing and the clip holds the mechanical connection. Plastic also expands and contracts noticeably with temperature — a long run moves several millimetres between a frosty night and a hot afternoon — which is why unions are designed with an expansion gap and the gutter is meant to be inserted only up to a moulded line. Get that wrong and the gutter binds, the joint is forced open, and the gasket loses contact. Age is the other cause: the rubber hardens, takes a permanent set, and stops sealing.

What usually causes it?

Perished or hardened rubber gasket that has lost its elasticity and no longer presses against the gutter
Gutter pushed fully home past the insertion line, leaving no expansion gap so the joint is forced apart in warm weather
Grit, moss or a leaf fragment trapped between the gasket and the gutter, or the gasket rolled out of its seat when the gutter was clipped in, holding a gap open
Joint under strain from a sagging run pulling on it, or from a missing bracket either side
Ladder or foot pressure distorting the union so it no longer holds the profile round
Mismatched components — a union from one manufacturer's system on another's gutter, so the profile does not seat
Silicone or mastic previously smeared over the joint, which cracks and then channels water out at one point

Is it dangerous?

Low risk to people, but do not dismiss it. A leaking joint drips onto the same square of ground and the same strip of wall constantly, and steady wetting in one place is worse for masonry than occasional heavy overflow. Where the joint sits above a doorway or path, winter drips freeze into a slip hazard. Where it sits against a wall, you get a persistent damp stripe, moss growth and eventually penetrating damp inside. If the drip is landing at the base of the wall near the damp proof course, it raises the ground moisture right where you least want it.

Can I fix it myself?

This is one of the more realistic homeowner jobs, at single-storey height with safe access. The usual fix is to unclip the gutter at that union, clean the gasket seat and the gutter end thoroughly, and either reseat the existing gasket or fit a new one — replacement gaskets and unions are sold for all the common domestic systems. Check the insertion line while it is apart and leave the expansion gap the manufacturer marks. What does not work is sealant over the outside of a joint: it bonds unevenly, cracks with the expansion the joint is designed to allow, and turns a spread drip into a concentrated jet. At two-storey height, get someone with proper access.

When should you call a fascia, soffit and guttering installer?

Call when the leak is at two-storey height, when several joints are going at once, or when the run is sagging and pulling the joint open — that last one is not a gasket problem and a new gasket will not hold. Also call if the wall or fascia below the drip is already showing damp, moss or soft timber, so the secondary damage gets looked at rather than just the joint. A single accessible joint on a garage or extension is fair game to try yourself first.

What will the fascia, soffit and guttering installer actually do?

Access the joint safely and dismantle it rather than sealing over it
Clean the gasket seat and gutter ends, and replace the gasket or the whole union with a matching component from the same system
Re-assemble to the moulded insertion line so the expansion gap is correct for the run length
Check bracket spacing either side of the joint and add brackets where the joint is carrying load it should not
Correct the fall along the run if the joint is being strained by a dip, removing any old mastic or silicone bodges, since these prevent a clean reseat
Check the fascia and wall behind the drip for rot and damp caused by the leak

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Sagging GutterCaution Rotten Fascia BoardCaution Cast Iron Gutter Leaking Or CrackedCaution

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