A thin green bloom on a concrete tile roof is cosmetic. Thick clumps that bridge the tile laps are not, because they hold water against the tile and drop into the gutter every time it rains hard.
The three stages
Stage one is surface staining. Stage two is cushion moss sitting in the pan of the tile. Stage three is moss growing over the lap and under the tile edge, which is the point where water can track sideways instead of running off.
This guide sits under our Roof Cleaning work, covering 20-mile radius of Plymouth.
What we remove and what we leave
We scrape and soft-treat rather than blast. Concrete tiles lose their factory face under high pressure, which makes the next moss colony arrive faster. Slate is treated even more gently.
Gutters come with it
Any roof clean puts debris into gutters. We clear and flush them as part of the job rather than leaving you a blocked run to deal with.
Questions we get on this
- Should I get the roof scraped or treated?
- Heavy moss usually needs both: mechanical removal first, then a biocide so what is left dies rather than regrows.
- Do you walk on the roof?
- Only where it is safe and the covering allows. Otherwise we work from ladders, a tower or a long-reach system.
- How often is sensible?
- On a shaded South West roof, a check every three to five years is normally enough after the first proper clean.
Related reading
- Flat roofs, valleys and where water actually goes wrong
- Chimneys, ridges and the growth nobody can see
- Bungalows: low roofs, long gutters and big driveways
- Garages, sheds and outbuildings