The short answer
Gutter joints leak because the seal has perished, the gutter has moved, or debris has stopped the water flowing past. Each joint relies on a rubber seal or sealant to stay watertight, and those wear out. Resealing can cure a single joint, but a run that leaks at several points, or sags between brackets, is usually telling you to replace the gutter.
A drip from a joint is rarely a mystery. The work is in telling a worn seal from a gutter that has moved or is full.
How a gutter joint is meant to work
Gutters are sold in lengths, so a house has joints wherever one length meets the next. On a modern plastic gutter, a joint is usually a union bracket that clips over the two ends with a rubber seal inside. Older cast iron gutters are bolted at the joints, with sealant or putty between the faces.
What stops a joint leaking?
Pressure and a seal. The rubber or sealant fills the small gap between the two ends, and the bracket holds them tight together. If either goes, a gap opens, and water finds it. The sideways drip appears at the underside of the joint first, then trickles down the face of the gutter and the fascia.
A joint is also the lowest-tolerance part of the run. The two ends must be level with each other and in line, and any difference in height gives water a lip to catch on. If the ends are misaligned, no amount of sealant will hold for long.
Where your gutter has lots of joints and runs for a long distance, the odds of one failing rise with age. Our page on cast iron gutter repair covers the older bolted kind in more detail.
Perished seals and worn sealant
The most common cause is simple age.
Why do the seals fail?
Rubber hardens, shrinks and cracks with sun and frost, and sealant dries out and splits. Once the gap is open, water runs out under pressure of its own weight. You will often find the seal looks brittle or has pulled away from one end when a roofer lifts the clip.
The giveaway is a drip that appears only when it rains and stops soon after. A joint that weeps for hours after rain is holding water, which points to a different cause.
If the rest of the gutter is sound, the cure is straightforward. The joint is cleaned back, any damaged parts are replaced, and a new seal or fresh sealant is fitted before the bracket is clipped back on. Sealant smeared over the outside of a leaking joint rarely lasts, because the seal that matters is on the inside. A genuine repair means opening the joint up.
A badly corroded cast iron joint is another story, because the metal itself may have gone. When iron has flaked at the bolt holes, a new seal has nothing sound to bed against, and the section needs repair or replacement instead.
Movement and sag
Even a good seal fails if the gutter moves.
Can a gutter pull itself apart?
Yes. Plastic expands and contracts with temperature, and a run that is fixed too tightly pulls at its joints through the seasons. Brackets that loosen let a length drop at one end, which opens a gap on top and pinches the joint underneath. Wind, ladders against the gutter and the weight of a blocked channel can all do the same.
You can see it from the ground. Look for a gutter that dips between brackets, a joint where one side sits lower than the other, or brackets pulling away from the fascia. If the fascia board behind is soft, the screws have nothing to hold and the whole run is working loose.
So the board gets examined along with the joint. A reseal on a sagging gutter will leak again within months. Re-fixing the brackets, correcting the line and sometimes renewing the board is the lasting fix, and our answer on gutter fall explains how the slope should sit once the run is straight.
Debris, blockages and what to do
Sometimes the joint is fine and the water is going the wrong way.
Is the leak really the joint?
A blocked outlet or full channel pushes water up and over, and it escapes at the weakest point, which is often a joint. The leak looks like a joint fault but clears when the gutter is emptied. Leaves, moss and silt are the cause, so clear the run first and watch it in the next shower. Our answer on overflowing gutters helps with that.
If the joint still drips with a clear gutter, the seal or the alignment is at fault. One joint on a sound gutter is a small repair. Several leaks along one run, a gutter that has gone brittle, or one that has sagged badly, means a repair is chasing a failing system.
We inspect the run from close range, photograph the joints and the fascia, and tell you whether a reseal is enough or a replacement makes better sense. One written price follows. Our gutters, soffits and fascias page sets out the wider roofline work.
More on leaking joints
Can I seal a leaking gutter joint from a ladder?
Sealant smeared on the outside will only buy a little time. A proper fix opens the joint, cleans it and renews the seal, which means working at height with both hands free. For safety and a lasting result, a tower or scaffold beats a ladder, and a roofer can do the job properly.
How do I know whether to reseal or replace?
One leaking joint on a sound, straight gutter is a reseal. Several leaks, a sagging line, cracked plastic or rusted iron points to replacement. The survey sorts it out: we look at the whole run and the board behind it, and the written price reflects what we find.
The full picture: Gutters, soffits and fascias in Taunton ยท More short answers