In our professional opinion, it is never okay to leave moss on a flat roof, or any other type of roofing system. While moss lacks true roots, it anchors itself using tiny structures called rhizoids. These rhizoids behave like roots by gripping tightly to surfaces and can penetrate small cracks or lift areas where the roofing material is beginning to separate. Over time, these rhizoids can widen cracks and contribute to the long-term deterioration of the flat roof’s surface.

Another significant issue caused by moss on flat roofs is its ability to retain moisture. Moss naturally holds water, which keeps the surrounding roof area damp. This delays drying and creates an environment where new moss growth thrives. During colder months, this trapped moisture can freeze and expand, causing both the moss and water to expand inside cracks. On newer flat roofs, this may not be immediately damaging, but on aging or slightly compromised surfaces, the expansion can worsen existing cracks and eventually lead to water ingress inside the building.

Because of these issues, we strongly recommend removing moss from flat roofs as part of routine roof maintenance. To ensure thorough cleaning and prevention, we advise using Baticlean CR, a specialized biocide treatment. This product stops moss growth, helps clean the surface, and prevents new moss from developing. Baticlean CR should be diluted as per instructions and applied to a dry surface. For best results, repeat the application every 6–12 months to maintain a moss-free flat roof and protect your property from long-term damage.