Is Moss on a Roof in Cwmbran Actually Harmful?

Roof Moss Removal › Cwmbran › Guide

Drive round Cwmbran and you will see plenty of roofs with a green or black coat on the north slopes. Whether that matters depends on how thick it is, what the roof is made of and where the water goes. This guide explains the damage moss can do and when it is simply surface growth.

What moss does to a concrete tile

Most Cwmbran houses from the 1950s to 1970s wear concrete tiles, and concrete is porous. Moss grows in the rough surface, soaks up rainwater like a sponge and holds it against the tile for days after the rain has stopped. That constant dampness is the real issue. A tile that stays wet takes in water, gets heavier and wears faster, and moss roots work into the surface and the joints between tiles.

Frost, valleys and blocked water

When a cold night follows a wet spell, the water trapped in moss and in the tile freezes and expands. Over several winters that flakes the tile edges and can crack them, and the cracks let water through to the battens. Moss also drops and washes down into valleys and gutters. A packed valley sends water sideways under the tiles or over the edge, so you may see damp on a wall long before you see the moss as the cause.

• Thick moss along tile edges and in valleys
• Gutters overflowing at the same spot every wet spell
• Tiles that look lifted or tilted at the bottom edge
• Damp patches on ceilings below a mossy slope

When it is only cosmetic

A thin film of green on a few tiles, with clear gutters and no lifting, is mostly an appearance matter. It is still a sign that the roof stays damp, but it does not call for urgent work. Where it matters more is on shaded slopes under trees, such as the established gardens around Greenmeadow and Henllys, because the growth there is thick and returns quickly.

What we do about it

We do not jet wash. High pressure forces water under the tile laps and strips the surface from concrete tiles. We hand-clear and brush the moss, collect it, clear the gutters and valleys and then check each tile that was hidden. After that a treatment goes on to slow regrowth. It is not a cure that lasts forever, and shade and north-facing slopes bring moss back in time, so we tell you honestly how often to expect to revisit.

What you can check from the ground

You do not need to go near the roof. Look from the pavement or garden for thick growth along tile edges, green gutters or an overflow stain down the wall, and check your loft for daylight or damp patches. If you see any of those, call us for a proper look. We will tell you what is cosmetic, what needs attention and whether clearing now saves a bigger repair later.

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