Roof moss is not automatically a problem. A light green film on a north-facing slope is cosmetic. Thick cushions of moss that hold water against the tile, break up and wash into the gutters are a different story — that is a maintenance issue that gets more expensive the longer it runs.
Here is how to tell which one you have, without going up a ladder.
1. Moss visible above the tile line from the ground
If you can see mounds standing proud of the tiles from the pavement, there is enough growth to hold water. Concrete tiles are porous; water held against them freezes, expands and slowly breaks the surface down.
2. Moss and grit collecting in the gutters
Handfuls of moss in the gutter mean the roof is shedding. Every autumn clear that comes out full of roof debris rather than leaves is telling you the source is the roof, not the trees.
3. Lichen spotting on the tiles
The pale grey-green crusty patches are lichen, and it bonds far harder than moss. It cannot be scraped off without damaging the tile. This is exactly what a biocide softwash is for — it kills the lichen and the weather clears it over the following months.
4. Blocked or overgrown valleys
Valleys between roof planes carry a lot of water in a Kent downpour. Debris and moss packed into a valley pushes water sideways under the tiles. Water ingress on the ceiling below a valley is a common and entirely preventable call-out.
5. Green or black streaking on the north elevation
Algae grows where the sun does not reach. It is mostly cosmetic on tiles but it spreads, and it will move onto render, fascia boards and conservatory roofs on the same elevation.
6. A roof that looks a different colour to the neighbours'
Terraces and estates built at the same time with the same tiles are a useful control. If yours reads noticeably darker or greener than the houses either side, the growth is well established rather than seasonal.
7. You are selling, letting or refinancing
A mossy roof reads as a neglected house in photographs and in a survey, whatever its actual condition. A softwash and a gutter clear is one of the cheapest presentation improvements available before a property goes on the market.
How we clean a roof
We scrape or brush off the heavy moss where it is safe to do so, clear the valleys and gutters, then apply a biocide softwash across the whole roof to kill the remaining spores at root level. No pressure washing — pressure removes the protective granules from concrete tiles and takes years off the roof.
Access is by powered platform or tower where the pitch or height requires it, and all work is carried out fully insured.
The short version
- Moss standing proud of the tiles holds water — that is when it stops being cosmetic.
- Lichen needs a biocide, not a scraper.
- Clogged valleys cause more water ingress than tile wear does.
- Never let anyone pressure wash a tiled roof.
