Is It the Gutter or the Downpipe? Diagnosing a Blockage From the Ground

A gutter that overflows along its whole length is blocked. A gutter that overflows at one spot, repeatedly, in the same place, usually is not: the downpipe below it is. That single distinction decides whether the work is clearing the run, clearing the pipe, or neither, and you can make the call from the pavement in the rain without touching a ladder.

What is the one test that separates them?

Go outside during steady rain and watch where the water appears. A blocked run overflows in several places along its length, often first at the end away from the downpipe, because that end is the high end of the fall and the water backs up towards it. A blocked downpipe overflows at the one point nearest the outlet, or out of the hopper head above it, because the run fills from the outlet end backwards and spills at the first place it can.

Timing gives you a second reading for free. A blocked run starts overflowing within a minute or two of the rain getting going, because the debris is already holding water and there is nowhere for more to sit. A blocked downpipe takes noticeably longer, because the whole run has to fill before anything comes over the edge. If the gutter behaves for the first ten minutes of a downpour and then overflows at one end, that is the pipe.

• Where along the run the water first comes over, and whether it is one point or several
• Whether it starts immediately or only after a few minutes of steady rain
• Whether the downpipe is running at all, and whether you can hear water moving in it
• Whether water is coming out of a joint, a hopper or a swan neck rather than over the top edge
• Whether the same thing happens on the back elevation, which people almost never check

What a blocked gutter run looks like when it is dry

You can read most of it on a dry day if you know what you are looking at. The giveaways are all about the length of the run rather than any one point on it.

• Grass, moss or self-seeded sycamore visibly growing out of the top of the run
• A sag between two brackets, so the line dips instead of following the roof edge straight
• Debris hanging over the front lip, which means the run is full to the brim underneath it
• A dark tide line on the outer face of the gutter, marking where it habitually sits full
• A broad green or black stripe down the wall along a length of the elevation rather than from one spot

The sag is the one worth taking seriously. A run that has lost its fall holds water permanently even when it is clear, and that turns a cleaning problem into a hanging problem. Clearing it will help, and it will fill again faster than a level run, because standing water is what silt settles out of.

What a blocked downpipe looks like

The tells are all concentrated at one point. Water appears at a single place on the run and nowhere else. There is a gurgling or glugging noise at the top of the pipe during rain. Most tellingly, you get a gutter that is visibly not full of debris and still overflows, which is close to a definition of a downpipe fault.

The swan neck is the usual culprit on a Birmingham terrace or semi. That is the double offset that carries the pipe back from the eaves to the wall face, and leaf arriving from the outlet above cannot get round the bend, so it packs there. On houses with a hopper head, the hopper fills and spills down the wall behind it. Staining down the back of a pipe, or a fan of dark growth starting at a joint halfway down, is water escaping the pipe rather than a blockage at the top.

There is a free field test for this. Tap the downpipe with a knuckle from as high as you can reach down to the ground. A clear pipe rings hollow all the way. A blocked one gives a dull, dead note from the level the blockage sits at downwards, and you can usually find the top of it to within a few inches. That works on a plastic downpipe; cast iron sounds dull all the way down whether it is clear or not, so on an old iron pipe the test tells you nothing and the flush is the only check. It takes thirty seconds and it saves booking the wrong job.

What does the green stripe on the wall tell you?

Its position is the information, because algae only colonises where the wall stays wet, so the stripe is a map of where the water has been going.

• A broad stripe running along the elevation under the gutter line: the run itself is overflowing over a distance
• A narrow vertical stripe starting at one point at the gutter line: a single overflow point, so look at the outlet, the downpipe or a failed joint
• A stripe running down beside or behind a downpipe: the pipe is leaking at a joint, or a bracket has pulled and water is tracking behind it
• A stripe that starts halfway down the wall: a parted joint or a cracked section of pipe, and not a blockage at all
• A dark fan at the base of the wall rather than a stripe: the water is arriving at ground level and not getting away

Could it be the gully rather than the gutter?

This is the third problem and it is the one most often confused with the other two. The downpipe has to discharge somewhere: usually into a gully with a grating at the base of the wall, sometimes into a back-inlet gully, sometimes straight into a socket in the ground. If that gully is silted up or packed with leaf, water backs up and spills at the foot of the wall while the gutter and the pipe are both perfectly clear.

Look for puddling at the base of the downpipe, a gully still holding standing water hours after the rain stopped, or silt fanned out across the path. It is the worst place on the building to be putting water, because it saturates the base of a solid wall at ground level, which is where the wall has the least ability to dry. Clearing a gully is frequently a gloved hand and a bucket, and it is genuinely a job you can do yourself. If it also backs up when you empty a bath or a sink, that is a foul drainage problem rather than a rainwater one; check with Severn Trent about responsibility for shared drains before paying a contractor.

Why does it show up as damp on an upstairs bedroom wall?

Because a great deal of Birmingham housing has no cavity to stop it. Anything built before about 1920, which covers most of the terracing in Bearwood, Kings Heath, Handsworth, Small Heath and Sparkhill, is solid brick. Historic England’s guidance on damp in historic buildings puts the mechanism clearly: brick and lime mortar are porous, rain is absorbed into the outer face and drawn deeper by capillary action, and damp shows on the internal face when the wetting rate exceeds the drying rate. Defective rainwater goods are one of the listed causes.

The diagnostic value is in the geometry. The patch sits on the inside of an external wall, usually high and often in a corner, on the same elevation as the overflow and roughly below it. It darkens after several days of rain and fades during a dry spell. That weather tracking is the single most useful thing about it, and it is what a meter reading will not tell you. What that damp then goes on to cost, and why it is so often treated as rising damp, is covered in what the water does to the building while the gutter is full.

What can you safely check from the ground, and what can you not?

• The elevation during heavy rain, watched from across the road or the far end of the garden
• The downpipe, tapped from top to bottom with a knuckle
• The gully at the base, lifted and looked into
• Growth above the gutter line, and the straightness of the line against the roof edge
• Phone photographs at full zoom from the ground, which show far more than people expect

What you cannot establish from below is the state of the silt bed, because you are looking at the underside of a gutter and the debris is inside it. You cannot see whether the fall is still correct. You cannot see the back of the run, the fascia behind it or the condition of the brackets. And you should not go up to find out on a domestic ladder: what the safety rules actually say about ladders is worth reading before anyone goes anywhere near a stepladder with a bucket.

Why is clearing your own frontage usually wasted on a terrace?

Because the gutter is continuous and the water is not interested in the property boundary. On the terraced streets of Bearwood, Kings Heath, Selly Oak, Handsworth and Small Heath a single run can cross four or five houses with no stop end between them, and it falls to one or two downpipes that may not be on your house at all. Water backs up from the blockage towards the high end, so the overflow appears above whoever happens to be downhill of the problem.

Two practical consequences follow. Clearing your own four metres of a shared run is frequently money spent on somebody else’s blockage two doors along, and it will overflow again on the next heavy rain. And where a single downpipe serves a pair of houses, the fault is literally shared, so it is worth a conversation with the neighbour before either of you books anything. Doing a whole run in one visit works better and costs less per house, which is one of the few genuinely free savings in this trade.

What is not worth paying for?

• A gutter clearance where nobody flushes the downpipes afterwards to prove the run is actually flowing
• Any diagnosis of an internal damp patch made without someone looking at the elevation in the rain
• Clearing one house on a continuous terrace run when the blockage is somewhere else along it
• Refixing a downpipe bracket while the pipe behind it is still solid
• Repainting over a stain that reappears every November

The diagnosis costs nothing and it decides the job. If the answer is the run, that is clearing the run and flushing the downpipes; if it is the pipe, the run may barely need touching; if it is the gully, you may not need anybody. On the interwar semis around Northfield a side driveway usually means the whole perimeter is reachable in one visit, and on a terrace it is worth telling us how the back is accessed. Either way, tell us what you saw in the rain and where, and we will give you a price and an estimated time before we start rather than after. The seasonal side of it sits in our piece on clearing before the winter rain.

Gutter Cleaning in Birmingham: what we actually see

The three areas on this post are a fair cross-section of the problem. Bearwood, in B66 over the boundary into Sandwell, is dense terracing behind a busy high street, where a single gutter run can cross four or five houses with no stop end between them. Kings Heath, B14, is terraces and subdivided flats off the High Street. Northfield, B31, is mostly interwar and post-war semis with pebbledash upper elevations, a side driveway and a gutter you can walk the whole way round.

What all three have in common is that nobody finds out about a blockage until it rains properly, and by then the interesting question is not whether something is blocked but what. A full gutter and a blocked downpipe produce almost identical symptoms indoors and want completely different work outside. Getting that wrong is how people pay to have a clear run emptied twice.

We do this work across Birmingham and the West Midlands. If you want the detail on how we do it and what it costs, see our gutter cleaning service, or read about the areas we cover it in most: Bearwood, Kings Heath and Northfield.