Blocked Downpipe

What's happening?

A downpipe blockage almost always sits at a change of direction or a change of diameter, because that is where debris stops moving. The usual spots are the swan neck at the top where the pipe offsets back to the wall, any bend partway down, and the very bottom where the pipe enters a gully or a back-inlet. Below ground it gets less visible: the gully can be silted up, its grate blocked with leaves, or the underground drain itself obstructed by roots or a collapsed section. The diagnostic clue is where the water appears. Overflow at the gutter with a dry pipe means the top is blocked. Water spurting from a joint means the blockage is below that joint. Water pooling around the base means the gully or the drain below it.

What usually causes it?

• Compacted plug of moss and silt at the swan neck immediately below the gutter outlet
• Leaf mass wedged at a bend where the pipe changes direction
• Gully grate blocked with leaves and grit, or a silted gully trap that has never been cleared and holds solids below the water line, so water backs up out of the top
• Roots, displaced joints or a collapsed section in the underground rainwater drain
• Birds' nesting material dropped in from the gutter above, or a nest built in the top of an open hopper
• Frozen plug in winter where the pipe runs on a cold north-facing elevation and had standing water in it
• Rainwater downpipe wrongly connected into a foul drain or a soakaway that has stopped working

Is it dangerous?

The building risk is significant and often underestimated. A blocked downpipe puts a continuous column of water against the wall at one point, and where the pipe discharges at the base, saturated ground raises moisture against the damp proof course: a classic route to what looks like rising damp inside. Water spurting from a joint soaks a concentrated strip of masonry. If the problem is in the underground drain, repeated surcharging can undermine the ground next to a foundation. There is no direct injury risk from the pipe, but ice below a blocked pipe on a path is a genuine slip hazard.

Can I fix it myself?

Diagnose by watching, then try the accessible parts. Run a hose into the gutter outlet and follow where the water stops: that pins the blockage down in minutes and is worth doing before anyone quotes. Clearing a gully grate and scooping out a silted gully trap is a straightforward, ground-level homeowner job with gloves and a bucket, and it is the single most commonly neglected one. Downpipe sections on a domestic system unclip or unscrew, so a low-level section can be taken off and rodded through. What you should not do is force a rod hard down a full pipe from a ladder, or work at two-storey height on the swan neck.

When should you call a fascia, soffit and guttering installer?

Call within days if you cannot clear it from the ground, if water is spurting from a joint against the wall, or if the gutter above is overflowing every time it rains. Call sooner if damp is appearing inside on that wall or near the floor on that elevation. If water pools around the base of the pipe and does not drain away after the gully is clear, the problem is in the underground drainage rather than the downpipe, and that needs someone who can inspect and jet a drain.

What will the fascia, soffit and guttering installer actually do?

• Hose-test from the gutter outlet down to locate the blockage precisely rather than dismantling the whole pipe
• Clear the swan neck and gutter outlet, which is where most domestic downpipe blockages sit
• Dismantle and rod pipe sections as needed, replacing cracked or distorted lengths and any perished clips
• Clear the gully grate and trap, check the pipe is discharging into it properly rather than beside it, and advise on drain inspection where the gully still surcharges once the pipe above is clear
• Fit a leaf guard or balloon at the outlet where trees are the recurring cause
• Check the wall and any internal damp on that elevation, since a long-blocked downpipe is a common cause of penetrating and apparent rising damp

Who fixes this

• Downpipe repair and replacement
• Gutter cleaning

Questions people ask

Sources & References

1. Approved Document H: Drainage And Waste Disposal
2. PCA, Gutters And Downpipes: Easy Maintenance Checks
3. PCA: Investigation And Control Of Dampness In Buildings