Most homeowners lump lichen in with moss. They are different growths, though, and that changes how you should deal with them. Lichen forms crusty patches on the tile surface, rather than the dense green clumps that moss makes.
This post explains what lichen is, whether it harms your roof, and when treatment is worth paying for. We will also say plainly when leaving it alone is the right call.
What lichen looks like
The NFRC, the trade body for roofing contractors, publishes a guidance note on moss and lichens. It describes lichens as “leather-like incrustations on the surface” that “may be embedded into the substrate of the covering”. It says they are green, orange, grey or black.
Moss, however, looks quite different. The same note says mosses typically form dense green clumps or mats, and look brown when dry. If your tiles show flat, crusty patches, you are probably looking at lichen.
Why lichen settles on tiles
Tiles have a rough surface, and that is the starting point. Specifically, the NFRC note says the rough surface filters dirt out of rainwater. It adds that blown spores take root in that dirt.
Tile makers describe the same pattern. Wienerberger says moss and lichen thrive when dirt and debris settle on tiles, from nesting birds, loose vegetation and airborne dust. Marley says growth tends to flourish where trees are nearby and conditions are shady and damp.
The NFRC adds that north-facing slopes, which stay damp longer, may attract more growth. As a result, the same roof can show lichen on one slope and a clean surface on the other.
Is lichen actually harmful?
The honest answer is that it depends on how much there is. Marley says low to moderate moss or lichen growth is a natural part of ageing on many pitched roofs. It says this is not harmful to tiles or slates under normal circumstances, unless the build-up becomes severe and stops water flowing off.
Marley also says elsewhere that moss, algae and lichen growth can trap moisture and cause tiles to degrade over time. These two statements fit together. Light growth is mostly cosmetic, while heavy, long-neglected growth deserves attention.
However, moss is a separate question, and our post on whether roof moss harms your house covers it in more detail.
Why scraping is not the answer
Scraping is the obvious DIY response, yet it has real limits. The NFRC says moss can be scraped off by hand, but only with caution. Its advice covers moss rather than lichen, and it recommends supported crawling boards or ladders and as little foot traffic as possible.
Lichen can be embedded in the surface, which is our reason for caution here. As a result, hard scraping may reach the tile as well as the growth. Our post on DIY roof moss removal explains why the method matters so much.
Pressure washing is no better, because Marley says most roofing professionals do not recommend it. The NFRC says it can force water into the roof space, particularly when sprayed upward from ground level.
How professional treatment works
We treat lichen the same way we treat moss and algae. A team applies a biocide at low pressure, and the biocide kills the living growth. Rain then washes the dead material away over the following weeks.
However, heavy, established growth is a different case. For that, our moss removal service scrapes off the bulk by hand first, then treats the surface left behind. Every job carries our 5-year regrowth protection guarantee.
No treatment lasts for ever, and nobody should promise otherwise. Wienerberger says anti-moss treatments are not a permanent solution, and that ongoing monitoring and maintenance are still required. The NFRC also warns that chemical washes can harm plants and animals, so a good team protects planting and keeps run-off out of watercourses.
When to leave it and when to act
You do not need to treat every patch. Light lichen on a sound roof can usually wait, and we will say so at survey.
We suggest acting in these cases:
- Heavy growth that covers large areas of a slope.
- Growth that sheds into gutters and blocks them.
- Water that no longer runs off the tiles freely.
- A roof you want to look cared for, for example before a sale.
A free survey tells you which case applies. We will explain what we find and give a fixed price.
Common questions
Does lichen mean my roof is failing?
Not by itself, because Marley describes low to moderate growth as a natural part of ageing, and lichen alone is not a sign of a failing roof. A leak, a slipped tile or a blocked gutter is a separate fault, and a roofer should look at it.
Can I treat lichen myself from the ground?
We would not recommend it. Marley says you should not access the roof yourself to remove moss or lichen because of the inherent risks. Spraying upward from the ground has its own problem, since the NFRC says it can force water into the roof space.
Will lichen come back after treatment?
It can, particularly on shaded or damp slopes. That is why treatment is a way of slowing regrowth, not ending it for ever. For example, trimming overhanging branches and keeping gutters clear helps, and our guarantee covers significant regrowth for five years.
How do I know if my roof needs treatment now?
Look from the ground, using binoculars if you have them. Check whether growth is thickening along the laps and ridges, and whether debris is reaching the gutters. A survey gives you a clear answer, and it costs nothing.
Where we treat lichen
We cover Kent, Surrey, East Sussex and West Sussex. For example, we offer roof cleaning in Canterbury, roof cleaning in Ashford, roof cleaning in Dorking and roof cleaning in Lewes.
Before you book
A few related questions come up often. Many owners ask about whether roof biocide is safe for pets and plants before agreeing to treatment. If your walls also need attention, read about how to clean render without damaging it.
Timing matters as well. Think about roof cleaning around bird nesting season when you plan the work. When you are ready, ask for a free survey and we will tell you what your roof needs.