Leaking joints
Why does a gutter joint leak, and how is it fixed?
A drip from one spot along the gutter tells you where to look. Here are four reasons a joint lets go, and what puts each of them right.
The short answer
A gutter joint leaks because its seal has hardened, grit has lodged under it, the run has dropped out of line, or the two lengths have drawn apart in the cold. The repair that holds is to take the joint apart, scrub both ends, then fit a fresh union and seal and re-set any bracket alongside it. Sealant smeared on the outside holds a drip back for a time, but not for long.
5 min read ยท Part of Gutters, soffits & fascias
The four reasons a joint drips
Plastic guttering is joined with a union clip that holds a rubber seal. The seal keeps the water in, and the clip holds the two lengths together. When a joint drips, the failure is one of these four.
- The seal has hardened with age and no longer grips the plastic.
- Grit or leaf debris has lodged under the seal and holds it off.
- The run has dropped, so the joint sits low and carries a pool.
- The gutter has crept back out of the clip as the plastic shrank in the cold.
Look at where the water falls, because the spot gives the diagnosis. A drip from the underside of the joint points to the seal. A drip that appears only in heavy rain points to a pool at a low joint. A joint that is visibly open points to a union that has come apart. Note which one you see, and photograph it from the ground, since the photo helps us decide what to bring up the ladder, and whether a second person is needed.
How the repair is done
On a sound plastic run the method is the same each time, and it takes little time at the eaves.
- Clear the gutter either side of the joint and flush the grit out.
- Release the union clip and separate the two lengths.
- Clean both ends and the clip, and check the plastic for cracks.
- Fit a new seal, or a new union if the clip is worn, and snap the lengths together.
- Check the brackets either side and re-set any that have dropped.
- Run water through and watch the joint for a few minutes.
A bead of sealant over the outside is not on that list. It can hide the leak for a season, and it makes the joint harder to open next time, because the sealant has to be cut away first. It is a stopgap.
Where the joint sits above a low porch, a ladder reaches it. At a second-storey eaves, the job goes onto a tower or scaffold instead, so that both hands are free for the clip.
When it is more than a joint
The fall Brett Martin advises is 1 mm for every 600 mm, running to the outlet. A run that has dropped between two brackets loses that slope, and the joint at the low point holds water that ought to be running away, so the seal sits under standing water. Re-setting the brackets and correcting the fall takes that strain off, and with the water moving the new seal is no longer asked to hold a pool back. Our answer on why gutters overflow looks at the slope in more depth.
A joint repair is not enough in these cases:
- joints are dripping all along the run, so a new run makes more sense
- the plastic itself is cracked or brittle at the joint
- the fascia is soft, so brackets pull out as quickly as they are re-fixed
- the joint is on cast iron, which is bolted and resealed rather than clipped
A bolted iron joint is repaired differently: it is unbolted, cleaned to bare metal, resealed and closed with a new bolt, which our page on cast iron gutter repair sets out.
What you can do before we visit
Give us a head start by finding where the drip comes from. Run a hose along the gutter above the joint, or watch during a shower, and note whether the water leaves from the underside or the face. Check the downpipe too, since a joint that only leaks when the pipe is slow is really a blockage. Take a photo that shows the joint and the brackets either side of it, plus the length of gutter running away from it, which shows whether the run has dropped.
Look at the wall below the joint too. A streak of damp or green staining under a joint, repeated each time it rains, shows the leak has been going for a while. If the wall is wet inside as well, say so, because water behind a fascia can reach the rafter feet, and a joint repair alone may not be the whole job.
We then look at the board behind and the slope of the run, and tell you which way the verdict goes: a new union, a re-set run or something wider. The hub page on gutters, soffits and fascias shows how that decision is made, and the page on what a gutter repair costs covers the money side of a small job.
More questions
Can I stop a leaking gutter joint with silicone?
Only for a short time. The part that has failed is the seal inside the clip, so silicone outside does not replace it, and the bead makes the joint harder to open later because it must be cut away first. A new seal or union is the repair that holds, and on a sound run it takes little time.
Why does my gutter joint leak only in heavy rain?
In heavy rain the gutter carries more water, so a low joint fills and a loose seal weeps. It points to a dropped run or a seal that is only just failing. A choked outlet downstream gives the same result, so we check the outlet and the slope as well as the joint, and we run water along the whole run before leaving.
Tell us what's wrong with the roof.
You'll get one written total price.