Although moss only grows following lichen, it is rife especially in the UK on older buildings and in areas with trees. Similarly, it may take the form of a thin green film and then develop into bulky globs that retain moisture and crawl across lengths of tiles.
Wind and birds dispersal of moss spores. These patches rest on the roof surfaces that are damp and shaded. The most common causes include:
Less light: North-facing roof slopes and areas under trees remain wetter longer and develop more moss.
Rain, slow drying and clogged gutters = Wetness all the time.
Porous roofing: Roofing, including tiles and shingles become more weathered over time, that makes it agreeable for moss to adhere to.
Clogs: Leaves, dirt and other debris gets stuck in your gutters prohibiting water from flowing. This also gives moss a place to grow out onto the roof structure.
How to stop moss coming back
The answer is in removing the moss correctly and then taking action to stop it from nesting back on your roof as well. For Roof Cleaning Gloucester, visit https://www.stagsoftwash.com/residential/roof-cleaning-gloucester
Keep gutters and valleys clean so water runs off rapidly.
To maximise the airflow and light access, trim excess branches.
Use a professional moss removal method (usually an intermediate grade scraping, and not to be confused with aggressive power washing treatments).
Use a biocide to kill any remaining spores and retard regrowth.
If you are getting quotes, remember to clarify what is included in the after treatment as just clearing moss without prevention will almost always lead to it reappearing again soon.