Moss on a Medway roof looks harmless and isn't quite. What it does to tiles, when to treat it, and why pressure washing is the wrong answer.
Medway's damp, shaded slopes grow moss better than almost anywhere — especially on north-facing roofs in Walderslade, Hempstead and the tree-lined parts of Rainham. The question isn't whether it's there, it's whether it's doing harm.
What Moss Actually Does
- Holds moisture against the tile surface, keeping it wet far longer than rain alone would
- Roots into the tile surface and lifts the edges as it grows, creating gaps for water
- Sheds in quantity — and moss shedding is a leading cause of blocked gutters, more than leaves in many Medway gardens
- Hides damage. A slipped tile under a moss mat isn't visible from the ground or from the roof
Is It An Emergency?
No. Moss is maintenance you're overdue, not a callout. A mossy roof can sit for years without failing. But it's not nothing either — a heavy covering on an older roof is accelerating the decay of the tiles underneath it.
Do Not Pressure Wash It
This is the most common mistake, and it causes real damage. Pressure washing strips the surface off concrete tiles, blasts the granular coating away, and drives water up under the tiles and into the roof space. You end up with a roof that looks clean and ages twice as fast. Anyone offering to pressure wash a tiled roof is not doing you a favour.
What We Do Instead
A gentle manual scrape to remove the growth without damaging the tiles, then a biocide treatment that kills the moss roots and inhibits regrowth. The moss turns brown and washes off over the following months, and the roof stays cleaner far longer than a scrape alone. On badly affected roofs we'll also clear the gutters afterwards to catch what sheds.
If your roof has a heavy moss covering and you're not sure of the state underneath it, a free survey will tell you — often there's nothing wrong that a clean and a treatment won't solve.
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Costs and timings in this article are guides for Medway and Kent properties. Every roof is different — a survey is the only way to get an accurate figure.