When and how often should you remove moss from your roof?

The signs that it is time to remove moss

• Green tufts of moss or grey or yellow lichen on the tiles or slates.
• Gutters that overflow or get blocked with plant debris.
• A roof that stays damp long after the rain, or black streaks running down.
• Tiles that shift: moss holds water, which freezes and puts stress on the materials.

The right season

Spring and early autumn are the best periods: the moss is clearly visible and the weather allows work on a dry roof. An anti-moss or water-repellent treatment must be applied to a clean, dry roof, followed by a few days without rain. Periods of frost and strong heat are avoided.

How often?

There is no single rule. A roof that is well exposed and clear can last nearly ten years between two moss removals. Under large trees, on north-facing slopes or on the coast, work is often needed sooner. In the Nord and on the Opal Coast, damp and sea spray encourage regrowth: a visual check every year and regular preventive treatment avoid a major job.

Mistakes to avoid

• A badly adjusted pressure washer: it can wear the surface of the tiles, move parts and let water in under the roof covering.
• Climbing onto the roof yourself: falls from roofs are among the most serious accidents at home.
• A fibre cement roof from before 1997: it may contain asbestos. High-pressure cleaning and dry scraping are prohibited on it, and the work is reserved for trained people. Always mention it before any quote.

Moss removal, cleaning, treatment: what is the difference?

Moss removal takes off moss and plants. Cleaning also removes dirt and restores the colour of the roof covering. An anti-moss treatment slows regrowth, and a water repellent limits water absorption by porous materials. They complement each other and are chosen according to the condition and material of the roof.

Written by Gautier Lauwerier, President of Maison Owlaris, in Steenvoorde. Maison Owlaris works throughout Hauts-de-France. Updated in October 2026.