Scotland's damp, mild, shaded conditions are close to ideal for moss. North and west elevations in Glasgow and Lanarkshire can go from clean to carpeted in a handful of winters. The question is not whether you have moss — it is whether it is doing anything.
When moss genuinely causes damage
- It holds water against the tile or slate surface, accelerating frost damage over Scottish winters.
- Clumps break away and block gutters, downpipes and valleys, pushing water back under the tiles.
- It lifts the tail of slates slightly, letting wind-driven rain track upwards.
- Thick growth adds weight and hides the defects underneath it from any ground-level view.
When it is mostly cosmetic
A light green film on a concrete interlocking tile roof with clear gutters and sound pointing is not an emergency. Plenty of roofs carry moss for decades without leaking. The problem is that from the pavement you cannot tell which situation you are in.
Why pressure washing is usually the wrong answer
High-pressure water strips the protective surface from concrete tiles, forces water under slates, and can dislodge nail fixings and bedding mortar. Plenty of Scottish roofs that leaked for the first time did so the month after they were jet washed. Scraping and brushing, or a biocide treatment left to weather off, is gentler — and neither should be done before someone has actually looked at the roof's condition.
If a cold caller offers to clean your roof from the ground with a lance and no inspection, ask them what condition the tiles are in first. If they cannot tell you, they should not be spraying them.
See what's under the green
A drone survey photographs each elevation close enough to show cracked, slipped and delaminating units through and around the moss, plus the state of the valleys and gutter runs. Every defect is circled, described and graded, so you can decide whether you need a clean, a repair, or nothing at all. £99 residential, £149 commercial, report typically within one working day across Glasgow, Lanarkshire and Edinburgh.