Moss, gutters and downpipes: cleaning the whole roofline

Moss grows in cushions that hold a great deal of water and stay damp long after the rain has stopped. On the lower courses of a roof, the part that sits just above the gutter, the cushions are usually thickest, because that is where the water collects and drains slowest. As the growth ages, the lower layers die back and turn brown, and the whole mat loosens its grip on the tile surface.

From there it travels in three ways.

• Rain and wind. Heavy rain carries small crumbs and spores over the tail of the tile and into the channel. Gusts lift dry fragments and drop them along the eaves.
• Gravity. A thick mat on a steep slope can slide in a single piece once it is saturated, and the lowest courses are where it lands.
• Birds. Birds tear moss away for nests or to reach insects beneath it, and much of it drops straight down.

Overhanging branches add leaves, seed cases and twigs, and the mixture packs tighter than moss alone. Our guide to trees overhanging a roof covers that side of it.

What ends up in the gutter

When we open up a choked gutter we usually find a dark, spongy layer sitting in the base of the channel. Moss crumbs, grit washed off the tile surface, and rotted leaves form a compost that holds water and, in time, grows its own plants. Small seedlings in a gutter are a sign that the channel has been holding standing water and soil for a long while.

The outlet is the opening where the gutter empties into the downpipe, and it is the narrowest point in the whole roofline. A handful of moss and grit is enough to close it. Once that happens, the channel fills from the outlet backwards, and the next shower tops it up until the water spills over the lip.

Where the water goes next depends on the building.

• Over the front. The water falls past the wall and lands on the ground or the path, which is the best outcome of a bad situation. Over time it erodes the soil and can splash mud and algae onto the base of the wall.
• Behind the gutter. If the gutter is fixed tight to the fascia (the board that carries it), water can run back over the board and into the eaves, soaking the timber and the soffit (the underside of the overhang).
• Down the wall. Overflow at a joint or corner runs down the masonry, which on stone or brick shows as a dark, damp stripe with a green edge.

The harm builds over several winters: rot in fascia ends, staining that will not wash off, and damp patches indoors that are hard to trace back to a gutter. If water is already reaching the inside, our guide to a blocked downpipe explains what to check at the bottom of the run.

Weight and sag

A channel packed with wet debris is heavy. Plastic can drop mid-run, and a weak bracket on old cast iron can pull away from the fascia, leaving a low spot that holds water.

Removing moss from a roof moves it, and on a pitched roof it moves downhill. Hand scraping detaches the mat in strips that slide to the eaves. Brushing and soft washing carry loosened material down on the rinse water. Even a biocide treatment, which kills the growth in place, lets it die back and shed over the following weeks, so a gutter that looked clean on the day of the visit can pick up a second dose of debris later.

This is the main reason we treat the gutters as part of the roof clean and not as a separate errand. If the channel is blocked before the work starts, the rinse water and the loosened moss meet a full gutter immediately. They overflow, wash down the wall, and leave a mess that has to be cleared up on top of the job.

Protecting the roofline during the work

Before a slope is worked on, the channel is checked and, where the access allows, cleared of the worst of its contents so water can leave freely. Loose moss is guided into a bag or a tray at the eaves rather than allowed to wash into the outlet. Where the gutter is plastic, we avoid kneeling or standing on it, as a gutter bracket is built to carry water and not a person.

Our roof cleaning process guide sets out the full order of work. For this guide, the point is simple: the gutters are touched twice, once before the slope is worked on so they can carry water, and once at the end to clear what came down.

When the last section of roof has been treated, the debris that came down is removed by hand. A scoop or a gloved hand lifts the bulk of it out of the channel, working from the stop end towards the outlet so nothing is pushed into the downpipe. The bag is then carried off site with the other waste.

The sequence we follow

1. Remove the loose material from the channel by hand, starting at the far end.
2. Brush the base of the channel to lift the compacted layer, and scoop that out as well.
3. Clear the outlet and look down it with a torch to check the throat is open.
4. Flush the channel with a measured amount of water and watch it run to the outlet.
5. Check the joints and corners for drips, and note any that need re-sealing.
6. Check the base of each downpipe, where a shoe or a gully takes the water away.

The flush at step four is the test that counts. A channel that looks clear can still hold water if the fall has gone, and standing water along a run tells us where a bracket has dropped. Installation guidance from Brett Martin and FloPlast suggests roughly 1:600 to 1:350 towards the outlet, system permitting. That is a tiny slope, so one sagging bracket can leave a pool. Our guide to gutter fall covers how it is set and checked.

The downpipe is the part nobody looks at until the gutter overflows. Moss crumbs that survive the outlet collect at the first bend or where the pipe meets the drain, and a blockage there backs water up the whole run. Signs of a problem include a gurgling sound in the pipe during rain, a damp wall behind it, or water coming out of a joint partway down.

What we check

• That the outlet and the first metre of pipe are free of debris, which we can usually test by pouring water down and watching how it clears.
• That the pipe is firmly fixed with brackets and not pulling away from the wall.
• That the shoe at the bottom discharges into a gully or soakaway and not onto the base of the wall.
• That any rainwater hopper, the box at the head of a pipe on older properties, is clear of leaves and moss.

Old iron and stone buildings

Cast-iron downpipes on older houses can be rusted through at the back, where damp never dries, and hard rodding can crack them. If we find a pipe in poor condition, we tell you and show the survey photograph, and the repair goes into the quote. Our guide to cast-iron gutters covers when a section is worth repairing and when it should be replaced.

On a steep drive or terraced garden, the ground beneath the pipe matters too: water discharged onto a sloping path runs back towards the wall.

Clearing a channel does not always solve the problem. Once the debris is out, the condition of the gutter itself becomes visible, and some of what we see needs work that goes beyond a clean.

Common findings

• Leaking joints. Seals dry out and the joint drips at the same point every time it rains. A re-seal is often enough on a plastic system, while an old cast-iron joint may need re-bedding.
• Dropped brackets. A bracket that has pulled out of a rotten fascia leaves a low spot. Manufacturer guidance spaces brackets no further apart than 500 mm for a small system and no more than about 900 mm for a larger one, so a gap wider than that is worth correcting.
• Cracked or brittle sections. Old plastic that has become brittle can crack under the weight of wet debris.
• Rotten fascia or soffit. Long-term overflow shows up as soft timber behind the gutter.

MyBuilder's 2026 cost guide puts guttering at about £30 to £70 per metre and fascia at £80 to £150 per metre, as national ranges. Scaffold, which is needed for most of this work above single-storey height, is on top of that, at around £20 to £40 per m² of access. These are typical UK figures; the price for your house follows the survey.

Where gutter work belongs

Replacing a failed run during the roof clean saves paying for access twice. If the roof clean is already booked, we can tell you at the survey whether the gutters look likely to need attention, and photograph the sections in question. Larger gutter, fascia and soffit work sits under our guttering, soffits and fascias service, and our gutter cleaning guide covers the routine upkeep between roof cleans.

A clear gutter stays clear for a while, and how long depends mostly on the trees and the amount of regrowth on the slope above. A roof with fresh biocide treatment sheds less than one left untreated, so the work on the slope and the work on the channel support each other. How quickly the growth returns is its own question, answered in our note on moss growing back.

Timing the visit

Leaf fall is the main reason to think about the calendar. Clearing a gutter in early autumn and again after the leaves are down gives the winter rain a clear route. Our note on the best time of year to remove roof moss sets the seasons out in more detail.

Guards and their limits

Gutter guards, the mesh or brush inserts sold to keep leaves out, cut down large debris. Fine moss crumbs and grit still settle on or beneath the mesh, so a guarded gutter still needs a look.

What to watch for from the ground

• Water overshooting the gutter in steady rain.
• A green or dark stripe on the wall under a joint or outlet.
• Plants growing out of the gutter.
• A gutter that looks bowed or has a visible dip.
• Overflow at the same spot in every shower.

If you notice any of these, a photograph taken from the ground and sent through the enquiry form or WhatsApp tells us whether it needs a visit. The site is left clear, waste removed, and the work carries a 10-year workmanship guarantee in writing.