Gutters get cleaned. Downpipes mostly do not, and the underground stormwater line almost never does. Which is why a house can have gutters cleaned every year and still overflow in the first real storm.
The gap in a standard gutter clean
A typical gutter clean removes debris from the gutter trough. That is genuinely useful and it is not the whole system.
The water still has to get from the gutter, down the downpipe, into the underground line, and out to the street or an absorption pit. A blockage anywhere along that path backs the whole thing up, and none of it is visible from the roof.
The only way to know is to flow test: put a hose into the gutter and watch what comes out at the bottom. It takes two minutes per downpipe and it is the difference between a gutter clean and a functioning drainage system. Any contractor who does not do it is cleaning the part you can see.
Where blockages actually sit
At the downpipe inlet. The most common, and the easiest to clear. Debris packs into the opening where the gutter meets the downpipe, especially where a leaf guard has been fitted badly.
At bends. Downpipes rarely run straight. Every offset around an eave or a window is a place material lodges.
Where the downpipe enters the ground. There is usually a transition from the metal downpipe to a PVC underground line, often with a reducer. It is a classic choke point, and it is below eye level so nobody looks.
In the underground stormwater line. Root intrusion, silt build-up, or a collapsed section. This is the expensive one and the one nobody checks until it floods.
At the discharge point. A kerb outlet buried under garden growth, or an absorption pit that has silted up and no longer drains.
The signs
- Gutter overflows in moderate rain despite being clean. The single clearest indicator.
- Water gushing from the top of a downpipe, or from a joint partway down.
- A downpipe that stays dry while others run during rain — it is blocked above.
- Water pooling around the base of a downpipe, or bubbling up from the ground near it.
- A persistent damp patch on the wall beside or below a downpipe.
- Gurgling from the downpipe during rain, which means partial blockage.
- Mosquitoes around a downpipe base — standing water that is not draining.
Why it matters more than it sounds
Overflowing gutters do not just make a mess.
Water going over the back of a gutter runs into the eaves and the wall cavity, which is a common cause of interior ceiling mould — see mould on a bathroom ceiling and what mould removal costs.
Water discharging at the base of a wall rather than into the drain soaks the ground against the footings. On older brickwork that feeds rising damp and salt attack — fretting brickwork and efflorescence both trace back to this.
And on a reactive clay site, which describes much of Sydney, concentrated water against a footing causes differential movement and cracking. That is a structural cost arising from a $200 drainage problem.
Clearing one
At the inlet: clear by hand from the gutter, then flush with a hose.
In the downpipe: a hose pushed up from the bottom, or a plumber’s snake fed down from the top. Compressed air can work and can also blow a joint apart, so go gently on older PVC.
At the ground transition: there is often a removable section or an inspection point. Sometimes the downpipe has to be disconnected to get at it.
Underground: this is a plumber’s job. A jetter clears silt and small roots; a camera is worth the money before anyone starts digging, because it tells you whether you have a blockage or a collapse.
Root intrusion generally comes back unless the tree or the pipe situation changes. If a jetting clears it every two years, that is the pipe telling you something.
Prevention
Clean the gutters on a real schedule rather than when there is a problem. Under heavy canopy that means two or three times a year — see how often gutters should be cleaned in Sydney.
Fit leaf diverters or downpipe guards at the inlets, and check them, because a blocked guard is a blockage.
Keep the discharge point clear. A kerb outlet swallowed by agapanthus is a blocked system.
And have the downpipes flow-tested every time the gutters are done. On our jobs that is standard rather than an extra, because a gutter clean that does not confirm the water gets away is only half the job. See gutter cleaning.
If you are also dealing with a gutter rusting through at the same time, that is covered in rusting gutters.
