Lichen looks stubborn on a roof because it is: those crusty, often orange or grey-green patches are actually a combination organism, part fungus, part algae, gripping tightly into the surface texture of the tile. Scraping it off the top layer, which is what most DIY attempts do, leaves the root structure very much alive underneath.
This guide explains why lichen is tougher to shift than moss or algae, why scraping alone almost always fails long-term, and how a proper biocide treatment with the right dwell time actually kills it off.
Why lichen is different from moss and algae
Lichen anchors itself into the tile surface with root-like structures called rhizines, which can penetrate concrete tiles more deeply than moss ever does. This is why physically scraping lichen off, even thoroughly, usually sees it return within a season or two: the visible crust is gone but the anchoring organism underneath survives. It's also why lichen tends to look worse on older roofs than newer ones, since it's had years, sometimes decades, to establish and spread undisturbed.
It's also slower-growing than moss or algae, which is part of why homeowners often notice it only once it's well established and covering a significant area of roof, by which point it can be spread across several courses of tile rather than a single isolated patch.
Why scraping alone fails
Beyond leaving live lichen behind, aggressive scraping risks damaging the tile's protective granular coating or, on older concrete tiles, chipping the surface itself, which then makes the tile more porous and prone to further growth. It's also genuinely risky work: kneeling on a pitched, often slippery roof to scrape tile by tile is a serious fall hazard for anyone without proper roof access training.
Pressure washing has the same problem in reverse: it can blast the visible lichen off but drives moisture into any tile that's already had its surface compromised, and does nothing for the parts still gripping in the texture.
Biocide treatment and why dwell time matters
A biocide solution applied by sprayer penetrates into the lichen and its anchoring structure, and needs proper dwell time, typically left on the roof for several weeks to months depending on the product and severity, to work through to the root rather than just the visible surface. This is the part DIY approaches often rush, washing the treatment off too soon and only getting a partial kill.
Once the biocide has done its work, dead lichen can be gently brushed or left to weather off naturally over subsequent rain, without the aggressive scraping that risks tile damage.
Costs and when to call a professional
A full roof clean including lichen and moss treatment typically costs around £400-£1,200 or more depending on roof size, pitch and severity of growth. Given the fall risk of roof work and the patience required for proper dwell time, this is one of the clearest cases in exterior cleaning where DIY isn't recommended: it's a job for a biocide-trained professional with proper roof access equipment.
It's also worth setting realistic expectations upfront: heavy lichen coverage built up over many years may need more than one treatment cycle to fully clear, and a reputable roof cleaner will explain this honestly rather than promising a single visit will remove decades of established growth.
Frequently asked questions
Related guides
Get Your Free Quote!
Enter your details below and one of our experts will be in touch to discuss the work needed and give you your free no-obligation quote.