New, dry roof tiles are inorganic but get organic qualities when they
have been exposed to damp and dirt. Tarred roofs are organic since the
tar is produced from resin. The board is produced from wooden fibres.
The nutrients in dirt and damp further the establishment of fungus affections. The spores have by then gotten a strong grip on the surface. Scrubbing or trying to wash off the affections, only gives a temporal result. It there is also safety issues when above ground which is both costly and time consuming.
To permanently remove the spores and the fungus it is necessary that the roof is sanitized by sterilize all affections –the roof surface also becomes totally disinfected. The affections are eliminated and the maintenance work lessens.