We recommend using products such as our liquid IKO Pro Roof & Wall Cleaner (see product sheet attached) during roof maintenance to combat organic soiling. See an example below on a project with a roof with white finish. This product is an effective cleaner that is both bio-based and biodegradable.
A deviation of the water drainage system is necessary during and after the treatment of the roof (the product needs a few days to do its job and make the contamination disappear). Once the roof is clean again, the original drainage system can be reconnected.
Contact your IKO advisor for more information.