The clearest sign is water spilling over the front of the gutter when it rains. Others are plants or moss growing along the roofline, green or dark streaks down the wall, a downpipe that stays dry in a downpour, puddles or splashing at the foot of a wall, and gutters sagging between brackets.
In this guide
Is water spilling over the edge when it rains?
This is the surest sign. If water pours over the front lip of the gutter, rather than down the downpipe, something is stopping it reaching the outlet.
Pick a properly wet day and go outside for five minutes. Watch each run of gutter. A blocked gutter fills up behind the blockage and the water overtops the edge, often in one spot, usually close to the outlet above the downpipe. You might also see a sheet of water spilling over the whole length of a run if the gutter is full of silt along its length.
Overflow at a corner or a joint is slightly different. It can be a blockage, but it can also be a gutter that has lost its fall (the slight slope towards the outlet) or a joint that has separated. Our guide to why gutters overflow in heavy rain helps tell them apart.
Can you see plants or moss along the roofline?
If something is growing out of your gutter, there is enough soil-like silt in there for roots. That means the gutter has been holding debris for a long time.
Grass, small weeds and even tree seedlings can take root in gutter silt. From the street you see a fringe of green along the edge. Moss is the other giveaway: tufts of it hanging over the gutter edge, or lumps of it on the ground below that have dropped off the roof.
Moss on the roof itself does not always mean the gutter is blocked, but the two usually go together. As moss dries out it breaks away, slides down the tiles and lands in the gutter. More on that in moss in gutters.
Are there streaks or damp patches on the wall?
Green, black or white streaks running down the brickwork below a gutter usually mean water has been coming over the top or through a joint, again and again.
Water that runs down the same patch of wall each time it rains leaves a mark. On brick it is often green algae or a dark tide line. On render or painted walls it can be grey or black streaking. White, powdery marks can be salts drawn out of the masonry as it dries.
Inside, look at the walls directly behind any stained patch outside, especially at ceiling height upstairs. A damp patch there is worth following up, because the cause is not always the gutter.
Does the downpipe stay dry in heavy rain?
If the gutter overflows but the downpipe barely runs, the blockage is in the outlet or the pipe itself.
Stand next to the downpipe in a downpour and listen. A working downpipe gurgles and you can see water leaving the bottom, into a gully or a drain. A quiet downpipe while the gutter above is overflowing points to a blocked outlet or a blockage partway down the pipe, often at a bend.
Our guide to blocked downpipes covers how to check, and what usually causes it.
What else can you spot from the ground?
Gutters that sag between brackets, joints that drip after the rain has stopped, birds coming and going from the gutter line, and splashing or worn ground at the base of a wall.
- Sagging. A full gutter is heavy. Wet silt can pull a plastic gutter out of shape or bend its brackets.
- Dripping joints. Water that keeps dripping from a joint long after the rain stops may be sitting in the gutter because it cannot drain.
- Birds. Birds picking at a gutter are often after insects in the debris. Birds going in and out of the eaves may be nesting, which matters; see birds and bats.
- Splash marks. A trench in the gravel, splashed soil on the wall, or green paving at the foot of a wall shows where water has been falling from height.
What if you can’t see any signs at all?
Gutters can be well on the way to blocking without showing anything from the ground. If it has been more than a year, or there are trees nearby, it is worth having them checked.
Most gutters are above eye level and you only see the outside face. A gutter can be half full of silt and still drain in light rain. The first sign might be the first heavy storm of the winter. That is why maintenance advice tends to be based on time and leaf fall, not just waiting for an overflow.
Professionals often use an inspection camera on a pole to look into the gutter from the ground; see how gutter inspection cameras work. If you would rather check yourself, read the ladder safety guide first.
Key points
- Water over the front edge in rain is the clearest sign of a blockage.
- Plants growing in the gutter mean silt has been there a long time.
- Streaks down the wall show where water has overflowed repeatedly.
- A dry downpipe in a downpour points to a blocked outlet or pipe.
- No visible signs does not always mean clear gutters.
Quick questions
Can I check my gutters without a ladder?
Partly. You can watch them in heavy rain, look for plants and streaks, and listen at the downpipes. To see inside, a camera on a pole, a phone on a selfie stick from an upstairs window, or a professional inspection camera saves climbing.
Is one overflow during a storm a problem?
Not always. Very heavy rain can overwhelm a clear gutter for a few minutes. If it overflows in ordinary rain, or in the same place every time, it is worth checking.
Do new houses get blocked gutters?
Yes. Leaves and roof debris don’t care how old the house is. Newer roofs may shed less grit and moss, but trees nearby still fill gutters.
