Roof Moss: Is It Actually a Problem, or Just Untidy?

Roof moss is the most oversold problem in exterior cleaning. Plenty of doors get knocked in the west of Scotland by people insisting a mossy roof is days from disaster. Usually it is not.

That said, there is a real line between untidy and damaging, and it is worth knowing which side yours is on before you either spend money you did not need to or leave something that is quietly costing you more.

A light green film on the north-facing pitch, or patchy growth on a concrete tile roof, is doing nothing structural. Tiles are not being eaten. Water is still getting where it should. The house looks tired from the street, and that is the whole cost.

If you are selling, that cost is real enough. Kerb appeal is the reason a lot of roof cleans get booked, and it is a perfectly good reason.

Moss holds water against the tile, and on the shaded side of a roof it can stay saturated for most of a Scottish winter. Freeze-thaw cycles then work on a wet tile instead of a dry one, and older concrete tiles start to spall and crumble at the edges.

Clumps also break off and wash down into the gutters, which is how a moss problem becomes a drainage problem. If you are clearing the same downpipe every year, the roof is usually the reason. Our gutter cleaning work turns up moss from the roof more often than leaves.

Deep moss on a shallow-pitched roof can also lift the bottom edge of tiles and let water track sideways under the lap. That is the point at which it is genuinely worth dealing with.

Aiming high pressure at a roof does three things, all bad. It strips the granular surface off concrete tiles, which is the layer doing the weathering, leaving a rough face that holds moss better than it did before. It forces water up under the laps and into the roof space. And on an old roof it will crack and dislodge tiles outright.

Roofs are soft washed instead: loose growth removed by hand and scraper, then a biocide applied at low pressure. The biocide kills the moss, algae and lichen at the root and keeps working for months afterwards, so what is left dies back and weathers away over the following season rather than coming off in a single dramatic afternoon.

That is a slower-looking result and a far better one. Our roof cleaning works this way as standard, with gutter clearing included, because whatever comes off the roof ends up in them.

Be wary of anyone quoting a roof clean from the pavement without looking at the tiles or the pitch, anyone promising an instantly spotless roof from a single wash, and anyone recommending re-coating or "roof sealing" as the default. Coatings have their place on specific roofs and are oversold badly on everything else.

A straight answer about whether your roof needs doing at all is worth more than a cheap quote for work it does not need.

A soft washed roof with a proper biocide treatment typically holds for several years, longer on the sunnier elevations. Pair it with a gutter clear and soffit and fascia cleaning and the whole roofline stops looking like the oldest part of the house.

We will tell you honestly if yours does not need doing yet. Ask for a look and we will come back with either a price or a reason not to bother.