Why does moss grow on roofs?
Moss thrives where there is moisture.
Roof areas shaded by trees or nearby buildings may remain damp for longer, providing favourable conditions for moss to establish.
Once it takes hold, moss can spread across tiles and become quite thick.
Is moss automatically damaging?
Not necessarily.
A small amount of moss doesn't mean that a roof is failing or that the tiles need replacing.
However, heavy growth can retain moisture and add weight to the surface. Moss can also spread across the roof and become established around tile overlaps and other areas where it is difficult to remove.
The condition of the roof itself is important too. Older or already-weathered tiles may require particular care.
Should you pressure wash a roof?
Roof cleaning needs more consideration than cleaning a driveway.
Aggressive pressure can damage or disturb some roof tiles and can potentially force water into areas where it shouldn't go.
For this reason, roof cleaning should be approached according to the type and condition of the roof rather than simply using the most powerful available equipment.
What about soft washing?
Soft washing can be an appropriate option for some roofs because it relies on treatment and considerably less on aggressive pressure.
The exact approach should depend on the roofing material and the type and amount of organic growth present.
What should happen before cleaning?
A roof should be assessed before any cleaning work begins.
Things such as broken tiles, fragile areas, access, surrounding property and nearby vegetation should all be considered.
Roof cleaning also involves working at height, so safety is an important part of the process.