Moss loves the cool, damp side of a roof. It starts as a few green tufts and, within a few seasons, can cover whole sections of tiles.
Why moss is a problem
- It holds water. Moss acts like a sponge, keeping tiles wet for longer, which matters in freezing weather.
- It can lift tiles. As it grows between and under tiles it can push them out of line and let rain in.
- It blocks gutters. Clumps wash down into gutters and downpipes, which then overflow onto walls.
How it should be removed
Roofs need care. Blasting tiles with high pressure can damage their surface and force water under them, so the method should suit the roof: hand removal of thick growth, a controlled low-pressure rinse or a soft wash, followed by a biocide treatment that slows regrowth.
Once the roof is clear, the gutters should be emptied too, otherwise the debris just causes the next blockage.
Keeping it away
Cutting back overhanging branches lets in light and air, which moss hates. A biocide treatment every couple of years keeps it from getting established again.