Last reviewed: 2026
Moss itself rarely destroys a roof, but it holds water against the covering, dams the flow above gutters and hides defects underneath. It should be removed by hand or with controlled low-pressure methods — never by high-pressure jet washing, which strips tile surfaces and drives water under the laps.
Why moss builds up here
Cumbria, South West Scotland and the North East give moss everything it needs: high rainfall, mild winters and plenty of shaded, north-facing slopes. Textured concrete tiles and older, weathered surfaces hold moisture longest and colonise first.
When it becomes a problem
Thick growth at the tail of each tile slows water off the roof and pushes it sideways into the laps. Dislodged clumps then block gutters and downpipes, which backs water up against fascias and walls.
- Gutters overflowing during ordinary rainfall
- Green staining running down walls below the roofline
- Damp appearing at the wall head or top-floor ceiling edges
- Moss so thick that the condition of the covering cannot be assessed
How it should be removed
Careful hand scraping and soft brushing, working down the slope, protects the tile surface and the laps. Gutters and downpipes are cleared afterwards, because most of the debris ends up there.
High-pressure washing is quick and damaging: it erodes the weathering surface of concrete tiles, can break slate and forces water under the covering. If a quote leads with jet washing, ask what it will do to the tiles.