What moss actually does to a roof
Moss works like a sponge. It holds rainwater against the tiles for days after the rain has stopped. Through the winter that water freezes and thaws over and over, which can crack and flake tiles, especially older concrete and clay tiles. Thick moss can also lift tiles slightly, letting wind-driven rain get underneath.
It ends up in your gutters
As moss dries out in warmer weather, clumps break off and roll down into the gutters. Moss from the roof is one of the most common things we find when we camera-inspect blocked gutters. Clearing the roof helps keep the gutters clear too.
When roof cleaning is worth it
- There are thick cushions of moss rather than a light green tinge.
- Your gutters keep blocking with moss.
- You’re planning to sell, and want the house to look cared for.
- The tiles are in good condition and you want to keep them that way.
When it might not be
If the roof is near the end of its life, with lots of broken or slipped tiles, cleaning won’t fix that. In that case it’s worth having the roof looked at first. We’ll always tell you honestly if we think a clean isn’t the right answer.
How roof moss is removed
There are a few ways to do it, and the right one depends on the roof:
- Manual removal. Moss is scraped and brushed off the tiles by hand. It’s careful and controlled, and usually the first step.
- Soft washing. A low-pressure wash with the right cleaning solution. It suits older or more delicate tiles.
- A more intense wash. For heavy growth on sturdier tiles, using the right pressure for the surface.
- Biocide treatment. Applied after cleaning to treat the spores left on the tiles, which helps the roof stay cleaner for longer.
Every roof clean we do finishes with an environmentally friendly biocide treatment, and we photograph the roof before, during and after so you can see the work.
Will the moss come back?
Moss grows wherever there’s shade and moisture, so no treatment stops it forever. A biocide treatment slows it down considerably, and keeping gutters clear helps the roof dry out faster after rain.