The “Moss Drop”: Why Gutters Block in Late Winter (And How to Fix It)

You did everything right. You spent a cold afternoon in late autumn clearing out the mountain of leaves from your gutters, confident you were prepared for winter. Yet here we are in late January or February, and during the first heavy downpour, you see it: water cascading over the side of your gutters like a waterfall.

What went wrong? You’ve just experienced the “Moss Drop”- a common UK phenomenon that clogs gutters and downpipes, leading to water damage and damp.

At Plumbers 365, our drainage teams see the consequences of this every year. It’s more than just an overflowing gutter; it’s about the serious issues it causes below. Let’s dig into the problem and answer your most pressing questions.

Why are my gutters overflowing even though I cleaned them in Autumn?

Frost expands the moss on your roof, detaching it from the tiles. It then slides down into the gutter, creating dense “dams” that block flow as often observed by plumbing and drainage experts at Plumbers 365. 

• Freeze-Thaw Cycle: Throughout winter, water gets into the moss on your roof tiles and freezes. As it expands into ice, it loosens the moss’s grip on the tiles.
• Heavy Rain: The first heavy, sustained rainfall of late winter or early spring washes all this dislodged moss and debris down your roof in one go.
• The Dam: This heavy, wet, sludgy moss hits your clean gutter and instantly forms a dense dam, completely blocking the flow of water to the downpipe. Your gutter goes from clear to clogged in a single downpour.

What is a “hedgehog” gutter guard and does it stop moss?

A “hedgehog” gutter guard is a long, bristly brush that you lay inside your gutter channel. It stops leaves, but moss often sits on top of it, causing water to skate over the edge. According to drainage experts at Plumbers 365: 

• Does it work? It’s excellent at stopping large leaves from getting into the gutter.
• Does it stop moss? Not really. In fact, it can sometimes make the problem worse. The fine particles of moss and roof grit get trapped in the bristles, creating a perfect, soggy bed for more moss and weeds to grow directly in the gutter. They can be effective, but they still need to be removed and cleaned periodically.

How to stop moss from the roof blocking the downpipe?

According to drainage experts at Plumbers 365, the only way to truly stop the problem is to tackle the source: the moss on your roof.

• Professional Roof Cleaning: Having your roof professionally cleaned is the most effective method.
• Zinc or Copper Strips: A more long-term solution is to fit a zinc or copper strip along the ridge of your roof. As rain washes over it, it releases metallic particles that are toxic to moss and algae, preventing them from growing back.

For the downpipe itself, fitting a downpipe leaf guard or “balloon” guard at the top of the pipe can stop the largest clumps of moss from going down and causing a serious blockage.

Can I clean gutters from the ground without a ladder?

Yes, there are several tools available that make this possible and much safer according to drainage experts at Plumbers 365:

• Telescopic Gutter Scrapers: These are long poles with specially shaped tools on the end to pull debris towards you.
• Gutter Vacuums: A wet-and-dry vacuum with long-reach poles can suck the debris directly out of the gutter.

While these are safer than using a ladder, they can sometimes miss the most compacted sludge, and you can’t visually inspect the gutter as easily.

What is the best tool for removing wet moss from gutters?

Wet moss is heavy, slimy, and compact. If you’re working from a ladder, the best tool is a gutter scoop or a narrow garden trowel according to drainage experts at Plumbers 365. These are specifically shaped to fit into the gutter profile and are strong enough to scrape out the heavy, wet sludge. Always wear a good pair of waterproof gloves!

Why is there damp on my wall directly under the gutter?

According to drainage experts at Plumbers 365, this is a classic sign of penetrating damp caused by an overflowing gutter. The water cascades down the brickwork, and because bricks are porous, they soak it up. This moisture then travels through the wall to the inside, appearing as a damp patch, often with peeling paint or wallpaper. It’s a direct consequence of the gutter not doing its job. As often observed by drainage experts at Plumbers 365, when a gutter is blocked by moss, the water cascades over the back edge. It runs down the fascia and saturates the solid brick wall. Over weeks, this water travels through the masonry and ruins your internal decoration.

How to unblock a downpipe clogged with moss and mud?

Plumbers 365 drainage experts suggest that if the blockage is in the downpipe, the problem is more serious. You can try:

• Tapping the Pipe: Gently tapping the outside of the plastic pipe can sometimes dislodge a light blockage.
• Flushing from Above: Use a garden hose to force water down from the top (from the gutter). The pressure can sometimes shift the clog.
• Rods from Below: If there is an accessible shoe or bend at the bottom, you can try feeding flexible drain rods upwards to break up the blockage. Never rod from the top down, as you will just compact the moss further.

If these methods fail, the clog is too severe. You need a professional. Our engineers use specialist tools and high-pressure water jetting to clear even the most stubborn downpipe blockages.

Do copper wires on the roof stop moss growing?

While it is considered an old roofer’s trick where stretching a bare copper wire along the very top of your roof (the ridge line), you create a natural fungicide. But our drainage experts at Plumbers 365 consider this a common DIY myth because in practice, a single copper wire rarely releases enough particles to be effective over a whole roof. You would need multiple, thick strips to have any noticeable impact. A professionally installed zinc strip is a far more reliable and long-lasting solution.

How much does professional gutter cleaning cost in the UK?

The cost depends on the size of your house, its height, and how easy it is to access the gutters. For a standard two-storey, three-bedroom semi-detached house, you can expect to pay anywhere from £60 to £150. Larger, taller, or more complex properties will cost more. Consider the alternative: painting a water-damaged ceiling costs £200+, and repointing brickwork costs hundreds. Paying for an annual “Moss Drop” clean in February/March is preventative maintenance that saves you money in the long run.

Can blocked gutters cause subsidence or foundation issues?

While a blocked gutter won’t directly cause subsidence, it can be a major contributing factor over a long period according to drainage experts at Plumbers 365. When a gutter or downpipe constantly deposits a large volume of water in one specific spot next to your house’s foundations, it can wash away or “scour” the soil. In houses built on clay soil, this can lead to changes in the soil’s volume, contributing to foundation movement and, in the worst-case scenario, subsidence. 

From a Full Gutter to a Flooded Garden, We Can Help

While cleaning gutters is a job for a maintenance company, dealing with the consequences of a blockage is our speciality. When a clogged downpipe leads to blocked gullies, waterlogged ground, or internal damp, you need a drainage expert.

Plumbers 365 is on call 24/7 to solve the serious problems that start in your gutters.

• 24/7 Emergency Downpipe & Drain Unblocking.
• CCTV Surveys to check for damage caused by water saturation.
• Expert Diagnosis of damp issues related to drainage.
• Professional Solutions for all your drainage needs.

If the “Moss Drop” has overwhelmed your system, call Plumbers 365.