A light covering of moss is mostly cosmetic, but thick moss should be removed. It holds water against the tiles, blocks gutters and the channels water runs down, and can lift tiles when it freezes. The safest way to remove it is by hand, with scrapers and brushes, followed by a moss treatment. High-pressure jet washing is best avoided, because it can damage tiles and force water under them.
Does moss damage a roof?
Moss itself does not eat into tiles, but it causes problems in other ways.
It holds moisture
Moss acts like a sponge. It keeps tiles wet long after rain stops, and older clay tiles that stay damp can flake or crack in frost. It also stops the roof drying out properly.
It blocks water channels and gutters
Interlocking tiles have small channels that carry water down the roof. Moss growing in them can push water sideways and under the tiles. Clumps washed off by rain end up in gutters and downpipes, which then overflow. Our guide to overflowing gutters covers this in more detail.
It can lift tiles
Thick moss builds up in the gaps where tiles overlap. When it freezes and swells, it can lift the tile edges, letting wind-driven rain get underneath.
It breaks down ridge mortar
Moss on mortar-bedded ridges and hips can help crack the mortar, which loosens ridge tiles over time.
When should you remove moss?
As a rough guide:
- A thin, patchy film: usually fine to leave, but keep an eye on the gutters.
- Cushions of moss along tile edges: worth removing before winter.
- Moss in valleys, gutters or on ridges: remove it, as these are the places where leaks start.
- Moss with slipped or cracked tiles nearby: get the roof checked, because the damage may already have started.
North-facing slopes and roofs under trees stay damp and shaded, so they grow moss fastest.
How moss is removed safely
Hand removal
The most reliable method is to scrape and brush moss off by hand, working down the roof. This lifts the moss without forcing water up under the tiles. Debris is bagged or cleared from the gutters afterwards.
Moss treatment
After the bulk is removed, a roof-specific biocide or moss treatment is applied to kill the spores left behind. This slows regrowth, but it is not permanent, so roofs in shady spots will need attention again in time.
Why we don't recommend jet washing
High-pressure jet washing can strip the surface and colour from concrete tiles, wear away the face of clay tiles, and drive water into the overlaps and interlocks. That can lead to leaks inside. Tile makers generally advise against it. If any washing is needed, it should be gentle, low-pressure and directed down the roof, never upwards.
Gutters and checks while up there
A proper moss clean should finish with clearing the gutters and downpipes. It is also a good chance to spot cracked tiles, slipped slates and loose ridges. See our guide to slipped, cracked and missing tiles for what these mean.
Moss on different types of roof
The method changes a little depending on what your roof is made of.
Concrete tiles
Concrete interlocking tiles have a rough surface that moss grips easily, and moss gathers in the interlocks. Careful scraping clears it without wearing the surface.
Clay tiles
Older clay tiles can be soft and are easily cracked, so they need a gentle touch. Handmade plain tiles often carry lichen too, which is part of their character and is usually best left alone.
Slate
Slate is smooth and dense, so moss tends to grow in the joints and on the ridge rather than across the face. Slates are brittle, so nobody should walk on them.
Flat roofs
Moss and debris on a flat roof hold water and block outlets. Clearing them by hand, without sharp tools, protects the covering.
Should you do it yourself?
It is not a job for a ladder. Moss is slippery, tiles crack under foot, and falls from roofs cause serious injuries. A roofer will use safe access equipment and will avoid walking on fragile tiles where possible.
Preventing moss coming back
You can't stop moss entirely, but you can slow it down:
- cut back overhanging branches so the roof gets more light and air
- keep gutters clear so water drains away quickly
- have a moss treatment reapplied when regrowth starts to show
- get the roof checked annually, especially if it is shaded
In Essex, Hertfordshire and Cambridgeshire
Moss grows fastest where roofs are shaded by trees or sit in damp air, and parts of all three counties are both.
- Near Epping Forest: In Loughton and Buckhurst Hill, roofs get a lot of leaves, twigs and moss. Gutters and valleys block and moss lifts tiles in frost, so hand moss removal, roof treatment and regular gutter clearing make a big difference.
- Woodland towns: Hockley has Hockley Woods on the doorstep and plenty of mature garden trees, and Billericay has a lot of mature trees around Lake Meadows and Norsey Wood.
- Tree-lined garden city streets: In Welwyn Garden City, tree-lined streets mean plenty of leaves and moss on roofs and in gutters.
- Riverside homes: In St Ives, homes near the Great Ouse and its water meadows sit in damper air, which encourages moss and wears out mortar and lead over time.
How First4Roofcare can help
We remove moss by hand, apply a roof treatment and clear your gutters, checking the roof for damage as we go. Find out more about our moss removal and roof cleaning and gutter repairs, or book a free survey and we will tell you whether your roof needs it.