Most leaking gutter joints are either worn seals in plastic gutters, failed jointing compound in cast iron, or joints pushed apart by the weight of a blocked gutter. Clearing the gutter can stop a leak if standing water was the cause. If the seal itself has failed, the joint needs resealing or replacing.
In this guide
Is it a leak or an overflow?
A leak drips from under the gutter at a joint, corner or end cap. An overflow spills over the front edge.
Watch in rain or run water through the gutter. Water dripping from the underside at the same point every time, especially at a union (the clip that joins two lengths), a corner or an end stop, is a joint leak. Water spilling over the front lip is an overflow and usually means a blockage. A joint that drips long after the rain has stopped often means water is sitting in the gutter, because a blockage or sag is stopping it draining.
Why do plastic gutter joints leak?
The rubber seals in the unions wear, harden or slip. Gutters also expand and contract with temperature, and a full gutter strains the joints.
Plastic gutter lengths are joined with union brackets that contain rubber seals. Over years the seals harden and stop sealing, or the gutter creeps out of the union as it expands and shrinks with the seasons. A gutter full of wet debris is heavy, and can pull the lengths apart or twist a union. Debris trapped in a joint can also stop the seal sitting properly.
Why do cast iron gutter joints leak?
Cast iron sections are bolted together with a sealing compound, which cracks and dries out over time. Rust at the joint makes it worse.
Older homes with cast iron gutters often have leaks at the bolted joints. The fix is usually to undo the joint, clean it, apply fresh sealant and re-bolt it, which is a job for someone experienced with cast iron. The Society for the Protection of Ancient Buildings recommends regular maintenance of rainwater fittings on old buildings, including keeping cast iron painted to slow rust.
Can cleaning the gutter fix a leaking joint?
Sometimes. If debris was holding water at the joint, or a full gutter was straining it, clearing it can stop the drip.
Clear the gutter first and watch it in the next rain. If the leak stops, it was caused by standing water or debris in the seal. If it carries on, the seal has failed or the joint has separated, and it needs a repair. A camera look along the gutter during a clean often shows a joint that has dropped or opened.
How are leaking plastic joints repaired?
Usually by replacing the union or its seal, or refitting the gutter lengths so they sit properly in the union. Sealant is a short-term patch.
Gutter sealant applied over a leaking joint can work for a while, but plastic gutters need to move with temperature, and sealant can crack or peel. Replacing the union is often straightforward on modern systems, if you can get matching parts for your gutter profile. Brackets may need adjusting if the gutter has lost its slope. Either way, it means working at gutter height, so the ladder safety points in is it safe to clean your own gutters apply.
Is a dripping joint urgent?
Not usually an emergency, but don’t leave it for years. A joint that drips onto the same patch of wall or the ground beside it causes the same slow problems as an overflow.
A drip onto a path is a nuisance. A drip that runs back along the underside of the gutter onto the fascia, or down the wall, keeps those surfaces wet. Over time that can mean staining, algae and, on timber fascias, rot. If the joint is above a door or path, it can also make the ground slippery in winter.
Who fixes gutter joints?
Roofers, gutter fitters and general builders. Some gutter cleaners do small repairs; many don’t. Ask.
When you book a gutter clean, mention any leaks you know about. The cleaner can check them on camera and tell you whether clearing should help, or whether you need a repair. Full View Window Cleaning clears gutters; we’ll tell you if we see a joint that needs attention.
Can I check the joints from the ground?
Mostly, yes. In rain or with a hose run along the gutter, look along the underside for drips, and look at the wall and ground below each joint for stains or splashes.
A pair of binoculars helps on a two-storey house. Look for gaps where two lengths meet, unions that sit at an angle, and green or dark lines on the fascia below a joint. Note which joints drip and roughly where they are, so whoever looks at them can go straight there.
Key points
- A drip from underneath is a leak; water over the front edge is an overflow.
- Plastic joints leak when seals wear or the gutter creeps out of the union.
- Cast iron joints leak when the sealing compound fails.
- Clear the gutter first; if the leak continues, it needs repair.
- Sealant over a joint is a short-term patch.
Quick questions
Can I seal a leaking joint from the ground?
No. It needs to be cleaned and dried, then sealed or replaced, at gutter height.
Why does my joint only leak in heavy rain?
Water may be backing up behind a partial blockage, or the seal only fails when the gutter is deeper. Clear it and check again.
Do I need to replace the whole gutter?
Not usually. Most leaks are at a few joints, and those parts can be replaced.
