The short answer
Moss that blocks a gutter should be lifted out by hand and bagged, not flushed down the downpipe, where it jams the drain. After a roof clean, the loosened growth gathers along the gutter for weeks, so a second clear a few weeks later is sensible. Sagging runs, standing water and overflowing joints point to a gutter repair rather than more cleaning.
Where gutter moss comes from
There are two sources, and they need different answers. The first is the roof. Moss, lichen and the grit from tired concrete tiles are washed off by every shower, and the gutter at the foot of the slope catches all of it. Treat a mossy roof with a biocide and the dead growth releases in clumps over the following weeks, much of it ending up in the run below.
The second source is the gutter itself. A trough that holds a little water for days, because it has sagged or lost its fall, grows moss in the damp silt on its own floor. Leaves, seeds and roof grit settle into that silt and form a thick green mat that holds more water still.
Some of the green in a gutter is not moss but its cousin, lichen, a crusty growth that comes off the roof in flakes and settles like grey-green grit. Our guide to lichen on roofs explains how to tell the two apart, because lichen sheds more slowly and keeps turning up in the run for longer.
A blocked gutter overflows over the front edge or behind the back, and the water runs down the wall or into the fascia. Our page on trees that overhang a roof covers the leaf side of the problem, which is the other big contributor.
How we clear it during a roof clean
The order of work matters. The roof is cleaned first, working down the slope, so that nothing loosened later drops into a freshly emptied gutter. Only then is the run cleared.
Moss is lifted out by hand or with a scoop and put straight into a bag. It is not hosed along the gutter into the downpipe, because wet moss packs tight at the first bend and blocks the drain. Silt and grit are scooped from the floor of the trough, the outlets are checked with a clear flow of water, and the joints are looked at for leaks and drips.
Where we are already working with ladders or a tower at the eaves, the gutter clear costs little extra time. Cleaning the roof without clearing the gutter leaves the owner with the same problem within a few weeks, so we include it in the plan whenever access allows it. Because the roof sheds for some weeks after a biocide treatment, a quick second clear once that has settled is often worth it.
Signs the gutter needs repair, not cleaning
Cleaning solves a blockage. It does not fix a fault in the gutter. Watch for these.
- Standing water. Water left in the trough a day or two after rain means the run has dropped or was laid without enough fall. Manufacturers typically recommend a gentle fall towards the outlet, roughly 1:600 to 1:350 depending on the system.
- Sagging between brackets. Brackets are normally spaced no more than 500 mm to 900 mm apart, depending on the system. Wider gaps, or brackets pulling out of rotten fascia, let the gutter bow.
- Dripping joints. Perished seals and cracked unions leak at every joint, even when the trough is clear.
- Green or black staining down the wall. It tells you the gutter has been overflowing for some time.
A fall that has been lost is often a bracket or fascia problem rather than a gutter problem. If the fascia board behind is soft, refixing the gutter to it only postpones the failure.
Repair, refit or replace?
A single failed joint or a short sagging section is a repair: refix the brackets, reseal the union, reset the fall. When plastic has gone brittle and cracked in several places, when earlier patches have already failed once or twice, or when the fascia behind it needs replacing anyway, a new run is the better use of money.
For a sense of scale, MyBuilder's guttering guide, updated in August 2026, gives a typical UK range of £30 to £70 per metre for guttering replacement. That is a national figure, not a price for your house. Access to the eaves, the length of run, the number of corners and any fascia work change it, and so does the choice between plastic, aluminium and cast iron. Once we have seen the eaves, you get a single written total.
Gutters on a slate or tile roof also sit in a different position from those on a flat extension roof. If the run feeds a flat roof outlet, ask whoever quotes to explain where the water goes. Our guide to cleaning slate roofs explains why gentler methods suit the covering above the gutter.
Keeping the gutters clear afterwards
Most of the work is leaf management. Gutter guards or brushes can help where branches overhang, but they need checking too, because fine moss and seed can still collect on top of the mesh. Cutting back the trees is more effective than any accessory.
Fit the clearing to the seasons. A check after leaf fall and another in late spring catches the two heaviest drops. A quick look during a heavy shower shows whether any joint is dripping or any outlet is slow.
If you have solar panels, the gutter at the foot of the array collects debris from behind them, and birds often nest beneath the panels. Our page on bird-proofing around solar panels explains the options.
Do not lean a ladder on a plastic gutter to reach in. They are not designed to carry your weight, and a fall from height is the real danger. If gutters need clearing and you would rather not do it, ring 01793 626096, or send a picture by WhatsApp or the form, or return to the main roof cleaning and moss removal page to see how a visit works.