Lichen on Roof Tiles — What It Means

Lichen — the crusty, grey-green or orange patches on some roof tiles — indicates a clean-air environment and an established, stable tile surface. It's slow-growing but tenacious, and needs a different treatment approach to moss.

What lichen actually is

Lichen is a symbiosis between fungi and algae. It grows extremely slowly — often 1–2mm per year — and attaches tightly to the tile surface. Unlike moss, which lifts off relatively easily once killed, lichen crusts stay bonded to the tile even after biocide treatment.

Why it's harder to remove

Lichen's fungal component roots into microscopic tile-surface irregularities. Standard soft-wash biocide kills the algal partner but the fungal husk often remains visible for months. Full visual clearance typically requires either extended biocide dwell time or a second application 6–12 weeks after the first.

Does lichen damage tiles?

Less than moss, but not nothing. Very old lichen colonies do slowly erode surface coating on concrete tiles. On slate the effect is minimal. Cosmetically it's often the more visible issue.

Treatment recommendation

For lichen-dominated roofs we typically apply a slightly stronger biocide dilution and schedule a light re-treatment 8 weeks later. The two-step approach delivers noticeably better results than a single pass.

Get a free Nottingham roof quote

If you'd like a fixed-price quote for your Nottingham property, request a free roof inspection using the form on this page — we'll typically respond within one working day. Every quote is written, fully insured and includes gutter clearance as standard.

Frequently asked questions